ESC471H1
Engineering Science Capstone Design
Optical Tweezers Final Design Report
Date
December 21st, 2010
Group Members
Maryam Badakhshi
Shannon O’Keefe
Laura Poloni
Hasmita Singh
Instructors
Professor Foster
Professor Nogami
Client
Professor Bailey
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Table of Contents
Date ............................................................................................................................................................... 0
Group Members ............................................................................................................................................ 0
Instructors ..................................................................................................................................................... 0
Client ............................................................................................................................................................. 0
1. EXECUTIVE SUMMARY .............................................................................................................................. 1
2. Introduction/Background ...................................................................................................................... 2
2.1 – Purpose of the Optical Trapping Apparatus ................................................................................. 2
2.2 – The Need for Improved Laser Safety ............................................................................................ 2
2.3 –Optical Trapping Experiment ......................................................................................................... 3
3. LASER SAFETY OF OPTICAL TWEEZERS APPARATUS ................................................................................. 4
3.1 – Problem Overview............................................................................................................................ 4
3.2 – Requirements and Constraints......................................................................................................... 5
3.2 – Laser Safety Solution ........................................................................................................................ 5
3.2.1 –Open Beam Enclosure and Safety Interlock ............................................................................... 6
3.2.2 –Optical Fiber Enclosure .............................................................................................................. 8
3.2.3 – Total Cost of Safety Enclosures and Interlock ........................................................................... 9
3.3 – Assessment of Safety Enclosures and Interlock ............................................................................... 9
3.3.1 – Criteria and Constraints Assessment ........................................................................................ 9
3.3.2 – Design Features ....................................................................................................................... 10
3.3.2 – Comparison with Alternative Solutions .................................................................................. 11
3.3.4 – Future Improvements ............................................................................................................. 12
4. LABORATORY REQUIREMENTS, CRITERIA AND CONSTRAINTS ASSESSMENT......................................... 12
4.1 – Pre-Experimental Procedures ........................................................................................................ 12
4.1.1 – Presentation ............................................................................................................................ 13
4.1.2 – Laser Safety Quiz ..................................................................................................................... 13
4.1.3 – Pre-lab Exercise ....................................................................................................................... 13
4.1.4 – Safety Sheet ............................................................................................................................ 14
4.2 – Experimental Procedure ................................................................................................................ 14
4.2.1 – Student Manual....................................................................................................................... 14
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4.2.2 – TA/Instructor Manual.............................................................................................................. 18
4.3 – Post-Experiment ............................................................................................................................. 18
4.3.1 – Student Assessment ................................................................................................................ 18
4.4 – Demonstration ............................................................................................................................... 19
4.5 – Experiment Budgetary Analysis ..................................................................................................... 19
4.6 – Future Work ................................................................................................................................... 20
6. OVERALL FUTURE WORK AND CONSIDERATIONS .................................................................................. 20
7. CONCLUSION ........................................................................................................................................... 20
8. REFERENCES ............................................................................................................................................ 22
APPENDIX A – Requirements, Constraints and Criteria .............................................................................. 24
APPENDIX B – Design Drawings of Open Beam Enclosure.......................................................................... 27
APPENDIX C – Design Drawings of Optical Fiber Enclosure ........................................................................ 34
APPENDIX D – Total Cost of Safety Enclosures and Interlock ..................................................................... 44
APPENDIX E –Alternative Laser Safety Solutions ........................................................................................ 45
Alternative Solution #1 ........................................................................................................................... 45
Alternative Solution #2 ........................................................................................................................... 46
Alternative Solution #3 ........................................................................................................................... 46
Assessment of Implemented and Alternative Solutions......................................................................... 48
APPENDIX F – Student Manual ................................................................................................................... 49
APPENDIX G – Teaching Assistant/Instructor Materials ............................................................................. 49
G.1 – Pre-Experiment Presentation ........................................................................................................ 49
G.2 – Teaching Assistant Manual ............................................................................................................ 49
G.3 – Pre-Lab Exercise ............................................................................................................................. 49
G.4 – Post-Experiment Assessment ........................................................................................................ 50
APPENDIX H – Safety Sheet......................................................................................................................... 51
APPENDIX I – Laser Safety Quiz................................................................................................................... 53
I.1 – Laser Safety Quiz Questions ............................................................................................................ 53
I.2 – Laser Safety Quiz Solutions ............................................................................................................. 55
APPENDIX J – Sample Data.......................................................................................................................... 57
APPENDIX K – Existing Optical Trapping Lab Manual ................................................................................. 57
APPENDIX L – Modifications proposed by the client .................................................................................. 57
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1. EXECUTIVE SUMMARY
This design reports outlines the final safety interlock system and student laboratory manual which have
been developed to ensure that the Optical Trapping apparatus, purchased by the University of Toronto
Physics department, is safe and educational for undergraduate student use. These physical and
educational deliverables have been designed to meet the requirements, criteria, and constraints that
have been established in consultation with Professor David Bailey (Physics Department, University of
Toronto) and Dr. Sandu Sonoc (Certified Laser Safety Officer, Radiation Protection Service, University of
Toronto Physics Department). The optical tweezers apparatus is a cutting edge research tool newly
acquired by the university and will provide students in the Advanced Physics Laboratory with the
opportunity to combine the theoretics of physics, nanoengineering, and biomedical engineering in a
modern research environment. However, before this experiment is integrated into the undergraduate
curriculum, provisions must be made to ensure that the optical trapping laser beam is secure and will
not cause harm to the user.
In order to ensure that untrained Engineering Science and Physics students will be able to experiment
with the optical tweezers apparatus, a protective enclosure and interlock system has been designed and
implemented, enabling the re-classification of the apparatus into a Class 1 Working environment. The
enclosure surrounding the trapping laser provides a physical barrier to prevent all stray laser beams
from reaching the user. In addition, an interlock system is in place to ensure that the laser will only
operate when the protective enclosure is in place. Removal of this covering will immediately activate the
interlock and prevent the laser from turning on. This design successfully ensures that all users operating
the optical trapping device will be protected from optical rays and can therefore learn in a safe and
secure environment. The operational and design details of the interlock and protective enclosure can be
found in section 3 of this report.
In addition to fulfilling the technical laser safety constraints, our optical tweezer experimental design
also ensures that students will be able to apply the theoretical knowledge gained during the first two
fundamental years of studying Engineering Science and Physics at the University of Toronto in a
practical, real world research application. By manipulating the optical trapping apparatus in a safe and
knowledgeable manner, students will be able to apply previously learnt fundamental principles of
physics to determine and compare the various degrees of optical trap stiffness required to fix particle
position. A complete experimental protocol, teaching assistant lab manual, and safety quiz have been
developed and provided to instructors to enable the smooth functioning of this laboratory and ensure
that proper student safety protocols are obeyed.
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2. Introduction/Background
2.1 – Purpose of the Optical Trapping Apparatus
The University of Toronto Physics department has recently purchased an Optical Trapping Kit from
ThorLabs Inc, for undergraduate student use. The optical trapping apparatus makes use of a 980nm,
330mW laser to manipulate and trap microscopic particles as small as 10nm [S1], and is therefore
utilized in modern research facilities. The ability of the optical trapping apparatus to isolate and examine
the physical properties of single cells has expanded modern research in biological physics. Applications
of laser microscopy are currently used to sort cells and determine the cellular properties and motility of
motor proteins, thus undergraduate students experimenting with this device at the University of
Toronto will have the opportunity to be exposed to cutting edge research technology. By integrating a
modern field of research into the undergraduate academic curriculum, Engineering Science and Physics
students participating in the Advanced Physics Laboratory (APL) will be given the “opportunity to work
on an interesting and challenging experiment, deepen their understanding of the underlying Physics,
and further develop laboratory, analysis, and communication skills” [S2], and thus meet the academic
goals of the APL.
2.2 – The Need for Improved Laser Safety
In order to effectively meet the academic goals of the Advanced Physics Laboratory and enrich the
educational experience of the undergraduate Engineering Science and Physics students who participate
in the APL, it was of utmost importance that the trapping laser be developed into a safe and secure tool
for untrained student use. In its original unaltered state, students would be required to participate in
the University’s laser safety program and medical surveillance program prior to operating or working
with the system, to remain compliant with laser safety regulations. However, as this Optical Tweezers
experiment will be run as part of the APL, students will only be given one three-week period in which to
complete each experiment. As the laser safety training runs on a monthly basis, it is not feasible for
students to receive this training, and as a result, other design precautions were necessary to ensure that
the laser is safe for untrained student use.
The trapping laser used in the optical tweezers apparatus operates at a wavelength of 980nm, with a
maximum power output of 330mW. According to the manufacturer, this laser beam is predominantly
encased by lens tubes, is not operated at maximum power, and consists of a diverged and nonconcentrated exposed beam after encountering the sample [S3]. Thus, once the laser is enclosed to
prevent contact between the operator and the exposed beam, it can be classified as a Class 1 laser.
Lasers categorized as Class 1 are surrounded by a protective enclosure at all times during operation and
are therefore considered safe for use by untrained persons. However, once this protective covering is
removed, the system is categorized as a Class 3B laser (power is 5-500mW) and is considered hazardous
[S4]. As removal of this enclosure is necessary to perform beam alignment, the development of an
interlock system was essential to guarantee that laser operation will only occur when the enclosure is in
place and the open beam region is fully encased. The addition of this enclosure and interlock system
now provides assurance that students can operate the laser in a safe and secure manner within a Class 1
working environment. Details regarding the operation of the Optical Tweezers Interlock and protective
enclosure can be found in Section 3 of this report.
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2.3 –Optical Trapping Experiment
The original Advanced Physics Laboratory Optical Trapping Experiment was designed by Jimmy Shen,
under the supervision of Professor Ryu. This existing manual has been revised to include laser safety
requirements and additional criteria and constraints, which can be found in Appendix B of this report.
Additionally, application of the original procedure during the experimental process revealed several
errors concerning laser rating levels and operation. These errors have now been eliminated and the
laboratory procedure has been validated. The inclusion of a detailed, accurate procedure and
appropriate safety precautions allows the laboratory to be executed safely and with ease, while
simultaneously maintaining the challenge of determining the functionality of a complex apparatus.
The purpose of the optical trapping experiment is to capture and observe particles within the photon
electric field, generated from the trapping laser. The stiffness of the optical trap maintaining the fixed
particle position can then be determined. This stiffness, analogous to the spring constant, k, of Hooke’s
Law, establishes the rate at which a trapped particle responds to an applied force and moves through
the optical system [S5]. Focus was placed on using the Equipartition method to determine the stiffness
of the optical trap. By drawing upon the thermal and potential energy equations, required to determine
trap stiffness in the equipartition method, students will be able to directly apply the modern physics and
fluid mechanics principals taught during the second year of Engineering Science, in PHY294 and AER210,
respectively. This provides students with the ability to make connections between theoretical
knowledge and realistic applications, and thus evaluate learning progress. This concept of directing how
the optical trapping experiment is “perceived, learned, and used” by students is a fundamental concept
of user experience design, a subset of experience design that aims to affect “all aspects of the user’s
interaction with a product” [S6]. The purpose of drawing upon previous academic knowledge to make
use of cutting-edge research technology is to encourage students that the rigorous academic theory
completed in their first two years is indeed directly applicable to real-world applications.
In addition to redeveloping the experiment to ensure that students are able to understand the
usefulness of and purpose behind theoretical study, the newly designed laboratory manual also contains
additional sub-experiments which can be performed by the students and adapted to suit individual
learning styles. According to David A. Kolb’s Experimental Learning Theory, the processes by which
individuals conceptualize ideas and form conclusions vary and can be classified into 4 main learning
styles: the converger, accommodator, assimilator, and diverger [S7]. Therefore, to accommodate the
unique learning styles of students, our laboratory protocol and assessment will provide students with
the opportunity to demonstrate the knowledge they have gained in their own preferred method of
expression. Students will be permitted to choose which of the additional experiments they wish to focus
on, and can make this choice based upon individual preferences. Furthermore, upon completion of the
physical experiments, students will be required to draw their own conclusions regarding the
determination of optical trap stiffness. These conclusions can be formed in accordance with the
students’ preference. By drawing student attention towards the real-life applications of optical trapping
and designing the experimental procedure to ensure that students will be able to form experimental
conclusions in an individualized manner, the newly developed APL Optical Trapping Experiment will
maximize student learning and retention.
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3. LASER SAFETY OF OPTICAL TWEEZERS APPARATUS
Before the newly acquired Optical Tweezers apparatus can be utilized for its intended purpose in the
Advanced Physics Laboratory courses, it is necessary to ensure that the apparatus is safe for students to
use. The following outlines the design requirements and features of the solution implemented to ensure
the safe use of the apparatus.
3.1 – Problem Overview
The Optical Tweezers apparatus consists of the OTKB Optical Trapping Kit purchased from Thorlabs, Inc.
This apparatus utilizes a temperature stabilized 300 mW (max) SM fiber-pigtailed laser diode with a
central wavelength of 980 nm, labelled as component 1 in the schematic diagram of the apparatus
provided in Fig. 3.1 (a). The laser beam travels through an optical fiber to the FiberPort Collimator
(component 2), and after passing through the Beam Steering Mirror, the laser beam is exposed as it
passes through the Relay Lens I (component 3A) before reaching the Dichroic Mirror (component 4) [L1].
An image of the actual apparatus showing these components is provided in Fig. 3.1 (b).
There are two main issues that arise over this portion of the apparatus. First, the optical fiber connecting
components 1 and 2 is made of very thin layers of glass-like material (usually Silica), and must be
handled with care since it can be easily damaged if students were to accidentally pull on the fiber,
exceed the maximum loading rate or bend radius, twist the fiber, or drop an object onto the fiber [L2].
Additionally, if the optical fiber were to be damaged, the hazards associated with open fibers have the
potential to seriously harm students. Open fibers or fibers that are stripped, trimmed, or cut can result
in short, thin, nearly microscopic pieces of glass lying around the work area and can easily penetrate skin
if touched [L3]. For these reasons, it is necessary to enclose the optical fiber that steers the laser beam
from the laser diode to the FiberPort Collimator in the Optical Tweezers apparatus (shown in Fig. 3.1
(b)).
The second issue that must be addressed is the portion of the apparatus in which the laser beam is
exposed, that is, between the Beam Steering Mirror (component 3A) and the Dichroic Mirror
(component 4). This open-beam portion of the apparatus is labelled in Fig. 3.1 (b). With the laser beam
exposed, the laser is classified as Class 3B [L4]. In order for a student to operate a laser with this
classification, they are required to participate in the full day laser training session [L5]. This is not
feasible for students of the Advanced Physics Laboratory since each experiment in the course is
executed over a three-week period, and the laser safety training is held only once a month. Therefore it
is necessary to employ safety measures so that the apparatus can be re-classified as a Class 1 laser
system, and can be operated by untrained students wearing appropriate laser safety goggles. This
requires that the open-beam portion of the apparatus be enclosed and equipped with a key switch and
a safety interlock.
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Figure 3.1 Optical Tweezers Apparatus
(a) Schematic of the OTKB Optical Trapping Kit from Thorlabs, Inc. [L1]
(b) Components of the Optical Tweezers Apparatus that require modifications
3.2 – Requirements and Constraints
Table A1 of Appendix A lists the technical constraints that were defined during project definition. The
laser safety solution that was implemented was designed to satisfy these constraints.
3.2 – Laser Safety Solution
In order to enable students to use the Optical Tweezers apparatus in the Advanced Physics Laboratory
courses, the following safety measures were implemented:
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1. The Open-Beam portion of the apparatus was enclosed and equipped with a safety interlock;
2. The Optical Fiber component of the apparatus was enclosed.
Figure 3.2 shows the Optical Tweezer apparatus before and after the implementation of these safety
measures. The design of these safety features is discussed in greater detail in the following sections.
Figure 3.2 (a) Before implementation of safety enclosures; (b) After Implementation of safety enclosures
3.2.1 –Open Beam Enclosure and Safety Interlock
As previously stated, the open-beam portion of the apparatus (shown in Fig. 3.1 (b)) poses many safety
hazards for users of the apparatus due to the high power of the laser diode. With the laser beam
exposed, it is possible for users of the apparatus to accidentally insert reflective objects in the laser
path, causing reflection of the laser beam. Additionally, the wavelength of the laser (980 nm) is within
the infrared range of light and is not visible to the human eye, so there is a high probability that harmful
effects of stray beams will occur without the knowledge of the user. For these reasons, it is necessary to
prevent access to the open-beam portion of the apparatus. However, it is necessary that any enclosure
be removable to enable alignment of the laser should the need arise.
To address this issue, a removable enclosure was constructed that covers the open-beam portion of the
apparatus. This enclosure is shown in Fig. 3.1 (b), labelled as “Open Beam Enclosure”. To ensure that
this enclosure is in place while the laser is on, the enclosure was also equipped with a safety interlock.
This interlock ensures that the laser cannot be turned on if the Open Beam Enclosure is not in place as
well as automatically shuts off the laser if the Open Beam Enclosure is removed while the laser is being
operated.
Design Open Beam Enclosure
The specifications of the Open Beam Enclosure can be found in the design drawings in Appendix B.
These drawings were submitted to the Department of Physics Machine Shop for the fabrication of the
enclosure. Images of the enclosure are provided in Fig. 3.2.1.
The enclosure was constructed from opaque black Plexiglass (acrylic) obtained from Plastic World [L6].
The enclosure was designed to provide a tight fit around the existing components, as can be seen in Fig.
3.2.1 (b) and (c).
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Since the apparatus was assembled on an optical breadboard, the availability of threaded holes at 1 inch
intervals was taken advantage of to attach the enclosure to the table. 2-inch L-brackets were purchased
from Home Depot [L7], and one side of each L-bracket was adhered to the enclosure with E6000
Industrial Strength Adhesive [L8]. The L-brackets were attached to the enclosure so that the free side of
the L-bracket was parallel and flush with the optical breadboard when the enclosure was in place over
the apparatus. Bolts were then used to secure the slotted L-brackets to the optical breadboard, as
shown in Fig. 3.2.1 (c).
As shown in Fig. 3.2.1, an image of the apparatus that is covered by the enclosure was placed on the top
of the enclosure. This was done to ensure that the learning experience of the students performing the
experiment was not impeded by allowing them to see the components underneath (i.e. the Relay Lens
I). This will also satisfy students’ curiosity, and will limit the number of students that will want to remove
the enclosure to access the components underneath.
Figure 3.2.1 Open Beam Enclosure
(a) Top view of Open Beam Enclosure, (b) Back view of Open Beam Enclosure, (c) Side view of Open Beam Enclosure
Safety Interlock
The safety interlock takes advantage of the built-in interlock feature of the laser source. The LM13S2
Butterfly Laser Diode (shown in Fig. 3.2.12(a)) is equipped with a Remote Interlock Connector that
controls the on/off state of the laser. In order to the laser diode to be turned on, a short circuit must be
applied across the terminals of the connector [L9]. The laser diode is configured with a shorting device
installed in the Interlock Connector, allowing the laser to operate normally. This shorting device can be
removed by unscrewing it from the input, and the interlock feature can be used by installing a 2.5mm
mono phono jack into the input [L9], as shown in Fig. 3.2.12(b). The 2.5mm mono phono jack was
purchased from the Source [L10], and can be easily found at any electronics store.
The interlock circuit consists of 5 microswitches in series, as depicted in Fig. 3.2.13 (a). The
microswitches were purchased at Creatron Inc. [L11], and can be easily found at any electronics store.
These microswitches were placed along the edges of the Open Beam Enclosure, as shown in Fig. 3.2.13
(b). Microswitches were attached to the enclosure by creating notches in the side of the enclosure that
fit the microswitches and then attaching the microswitches with E6000 Industrial Strength Glue [L8], so
that the microswitches are embedded in the sides of the Open Beam Enclosure. This ensures a strong
adherence of the microswitches to the enclosure, preventing the microswitches from accidentally being
detached from the enclosure which removing/replacing the enclosure from its proper position.
Four microswitches were placed along the bottom perimeter and one along the interface between the
Open Beam Enclosure and the Optical Fiber Enclosure, as shown in Fig. 3.2.13 (c). This placement of the
microswitches ensures that the Open Beam Enclosure must be in place and secured to the optical
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breadboard in order for all of the switches to be activated. If all of the switches are not activated, a short
circuit is not created across the Interlock Connector, and the laser cannot be turned on. Similarly, if the
laser is on and the enclosure is removed, the microswitches will be de-activated causing a break in the
short circuit across the Interlock Connector, which will automatically turn off the laser.
(a)
(b)
Interlock Connector
Figure 3.2.12 (a) LM14S2 Butterfly Laser Diode with Interlock Connector; (b) Interlock circuit connected to 2.5mm mono
phono jack and inserted into the Interlock Connector
During operation of the Optical Tweezers experiment, it is intended that the Open Beam Enclosure will
always be in place. If a student wishes to perform alignment, the Teaching Assistant will be required to
supervise this, as well as remove/replace the enclosure. Instructions for doing so are provided in the TA
Manual in
Appendix ##.
Instructions on repairing components of the safety interlock are also provided in the TA manual.
(b)
Figure 3.2.13 (a) Interlock Circuit, consisting of 5 microswitches in series connected to the 2.5mm mono phono jack; (b)
Placement of microswitches along edges of Open Beam Enclosure; (c) Placement of microswitch along the interface of the
Open Beam Enclosure and the Optical Fiber Enclosure
3.2.2 –Optical Fiber Enclosure
As previously stated, it is necessary to enclose the Optical Fiber connecting the LM14S2 Butterfly Laser
Diode to the FiberPort Collimator to prevent damage to the fiber and prevent hazards associated with
open fibers.
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The specifications the Optical Fiber Enclosure (shown in Fig. 3.2 (b)) can be found in the design drawings
in Appendix C. These drawings were submitted to the Department of Physics Machine shop for the
fabrication of the enclosure. The enclosure was constructed from transparent Plexiglass (acrylic)
obtained from Plastic World [L6]. The enclosure was designed to completely cover the optical fiber as
well as the Interlock Connector and the portion of the safety interlock leading from the laser diode to
the Open Beam Enclosure (seen in Fig. 3.2.12 (b)). It was also ensured that the Optical Fiber Enclosure fit
together with the Open Beam Enclosure, so that when both enclosures are secured, the microswitch on
the side of the Open Beam Enclosure would be activated through contact with the Optical Fiber
Enclosure.
The Optical Fiber Enclosure was attached to the optical breadboard in the same way that the Open
Beam Enclosure (i.e. using slotted L-brackets).
3.2.3 – Total Cost of Safety Enclosures and Interlock
Table D1 in Appendix D provides a detailed break-down of the costs for the implementation of the
safety enclosures and interlock. From this, the total cost of $321, which is well below the budgetary
constraint of CDN $1000 (listed as Technical Constraint T6 in Table A1 in Appendix A).
3.3 – Assessment of Safety Enclosures and Interlock
3.3.1 – Criteria and Constraints Assessment
Table 3.3.1 lists the Technical Constraints that were developed during project definition (also provided
in Table A1 of Appendix A) along with an assessment of how the implemented solution meets these
constraints. From this, it can be seen that the implemented solution meets all of the technical
constraints.
Table 3.3.1 Criteria and Constraints Assessment
Item ID
Description of Constraint
Assessment of Implemented Solution
T1
The Optical Tweezers
experiment must be made
safe for undergraduate
students who have not taken
the full day laser safety
course and should be
classified as a Class 1 laser.
The light path where the
beam is exposed to air
should be enclosed.
The fiber optic should be
enclosed for protective
purposes. It would be helpful
to be able to observe the
fiber optic under the
By enclosing the open-beam portion of the apparatus with
opaque acrylic and equipping this enclosure with a safety
interlock, the Optical Tweezers apparatus is no longer
considered a Class 3B laser. The enclosure prevents users
from accessing the exposed laser beam, and the interlock
ensures that the laser will completely shut off if this enclosure
is removed.
The Open Beam Enclosure, shown in Fig. 3.2.1, encloses the
portion of the apparatus over which the laser beam is
exposed.
The Optical Fiber Enclosure covers the optical fiber with
transparent acrylic. This prevents students from tampering
with the optical fiber, while still enabling the students to
observe the component. This ensures that the learning
experience of the student is not at all impacted by the
T2
T3
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T4
T5
T6
enclosure.
The reflected beam should
not leak out from the sample
stage, and the user must be
able to move the sample
stage using the knobs.
Budgetary constraints:
Additional components onto
the existing apparatus
should not exceed CDN
$1000.
The design must prevent
students from inserting an
object into the path of the
laser which could cause the
beam to diverge.
implementation of the safety enclosures.
The safety enclosures that were designed and implemented
do not interfere with any other components of the apparatus,
so that the user is able to move the sample stage using the
knobs.
As shown in Table 3.2.3, the implementation of the safety
enclosures and interlock had a total cost of ~$320, which is
well below the budgetary constraint.
Since the portion of the apparatus over which the laser beam
is exposed has been enclosed and equipped with an interlock,
it is not possible for students to simultaneously have the laser
on while being able to access or interfere with the beam path.
3.3.2 – Design Features
Table 3.3.2 outlines the features of the safety enclosures and interlock that surpass the requirements
outlined in Table 3.2.1.
Table 3.2.2 Design Features of the Safety Enclosures and Interlock
Design Feature
Advantages
Sensitivity of
Interlock
The use of microswitches ensures that the interlock is very sensitive. Due to the
small size of the microswitches, any movement of the Open Beam Enclosure
from its proper position will disable the laser. Even if the bolts that secure the
enclosure to the optical breadboard are loosened, the laser will be disabled.
It should be noted that this sensitivity does not interfere with the functionality of
the apparatus, since once in place, the interlock is very reliable. When the Open
Beam Enclosure is secured in place, accidental forces applied to the enclosure
will not move the enclosure and disable the laser.
Placement of microswitches around the bottom perimeter and side of the
enclosure ensures that the enclosure must be in place over open-beam portion
of the apparatus.
The microswitch placed at the interface between the two enclosures makes it
extremely difficult for students to activate the microswitches when both
enclosures are not secured in place. This ensures that both enclosures must be in
place when the laser is on, which prevents students from tampering with the
portion of the interlock circuit that connects the Interlock Connector to the Open
Beam Enclosure.
The two enclosures were designed so that they would “fit together ” when
secured in their proper positions, as shown Fig. 3.2.2 below.
Placement and
Integration of
Microswitches
Integration of the
two Enclosures
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(a)
(b)
Figure 3.2.2 (a) Image of interface between enclosures when they are not in their proper
positions; (b) Image of interface between enclosures when they are secured to the optical
breadboard
Use of slotted Lbrackets to
attach enclosures
to table
By placing a microswitch at this interface, it is ensured that the Open Beam
Enclosure and the Optical Fiber Enclosure must both be in place in order for the
laser to be turned on. This will prevent students from damaging the interlock jack
and the connection from the laser diode to the Open Beam Enclosure. This also
prevents students from damaging the optical fiber while the laser is on, or from
unscrewing the optical fiber from the fiber port collimator while the laser is on.
This compensates for deviations in the positioning of the threaded holes on the
optical breadboard, and provides ease of use when removing/re-installing the
enclosures for beam alignment.
Simple design of
enclosures
By designing the enclosures so that they only cover the necessary portions of the
apparatus, it was ensured that the safety measures do not interfere with other
components of the apparatus. For example, access to the beam steering mirror
after the FiberPort collimator is maintained when the safety enclosures are in
place.
Additionally, the simple design of the two enclosures maintains the visual appeal
of the apparatus. By placing an image of the open-beam portion of the apparatus
on the Open Beam Enclosure and using transparent acrylic for the fabrication of
the Optical Fiber Enclosure, the students’ learning experience is not disturbed by
the safety measures implemented.
3.3.2 – Comparison with Alternative Solutions
An overview of the alternative solutions developed during project development and presented in the
project Proposal is provided in Appendix E. A comparison of the implemented solution and these
alternative solutions with respect to the technical constraints for ensuring laser safety is provided in
Table E1 in Appendix E.
From Table E1, it can be seen that the implemented solution is the only solution that fully meets all of
the technical constraints. All three of the alternative solutions do not automatically shut off the laser
when the enclosure over the open beam portion of the apparatus is removed; they each use a magnetic
mount that reduces the power of the laser beam. However, using a mechanical component provides a
greater potential for students to tamper with the apparatus. In all three alternative solutions, there is
the possibility of students removing the magnetic mount when the enclosure is removed. The
implemented solution avoids this issue, since when the enclosure is removed, the laser cannot be
turned on at all. By directly controlling the laser through the interlock connector, the implemented
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solution provides many advantages over the alternative solutions, as well as ease and simplicity during
the installation and for future modifications of the apparatus.
3.3.4 – Future Improvements
The design of the Open Beam Enclosure outlined in the Preliminary Design Report specified that the
enclosure would be constructed from a material with the appropriate optical density required for the
laser source of the Optical Tweezers apparatus. However, further investigation into such materials found
that this would cost several hundred dollars. In consultation with Professor Bailey, the coordinator for
the Advanced Physics Laboratory courses, it was decided that this was too expensive and that opaque
acrylic would be sufficient for constructing the Open Beam Enclosure. However, in the case that the
laser beam is misaligned and the Open Beam Enclosure is put in place over the apparatus, the next
student to operate the apparatus could be susceptible to stray laser beams, since opaque acrylic will not
filter the wavelength of the LM14S2 Butterfly Laser Diode. In future improvements to this apparatus, it
would be beneficial to construct the Open Beam Enclosure from a material with the appropriate optical
density (OD 6+ is required for a wavelength of 980 nm [L12]).
4. LABORATORY REQUIREMENTS, CRITERIA AND CONSTRAINTS
ASSESSMENT
The existing student manual for the Optical Tweezers was transformed into a reliable, organized, and
coherent manual that is usable by a modern student in the APL. This revised experiment, which is to be
carried out individually (E1), will provide a contemporary experiment for the APL and will allow the
visualization of theoretical concepts surrounding optical traps within a thoroughly tested, safe and
secure working environment.
The main objective was to focus on perform the Equipartition experiment successfully and address the
issues of insufficient procedural details, the lack of a Teaching Assistant Manual and the lack of safety
precautions and laser safety procedures. The revised experiment has been developed from the
perspective of the end-user experience and stems from the experimental criteria previously established
(Appendix A). The design of the Optical Tweezers experiment encompasses a holistic approach, in that
the pre-experimental context, experimental procedures, and post-experiment details were all accounted
for (Figure H2). The design process, rationale for decisions and key features of the design as well as
deliverables are discussed in the subsequent sections. Linkages to requirements will be demonstrated
through reference to the Requirement ID (eg. EP1), and a complete list of requirements, criteria and
constraints from the Preliminary Design Report can be found in Appendix A.
Figure H2: The experimental design encompasses the pre-experimental context, the experimental procedures and postexperiment considerations.
4.1 – Pre-Experimental Procedures
12
Prior to the beginning of the semester, TAs (and Instructors) must attend the full-day Laser Safety
Training course offered by the University of Toronto (Tr5). This is essential since the TA may be required
to perform procedures with an open beam. The TA supervising the Optical Tweezers experiments should
execute at the least the first portion of the lab (Equipartition experiment) such that he/she is acquainted
with the apparatus and experimental procedure to be capable of providing assistance to students when
necessary (Tr1).
The pre-experimental procedures include the delivery of a presentation by the TA, a laser safety quiz for
the student, a pre-lab exercise which the TA will briefly discuss, and a safety sheet stating the most
important safety instructions that are to be obeyed. These are discussed in detail in the subsequent
sections.
4.1.1 – Presentation
A presentation is delivered to the students by the TA to introduce the experiment. This includes a brief
overview of the theory behind optical trapping, its applications, and a walk-through of the major
components of the apparatus. The main emphasis is placed on laser safety, since students performing
this lab will not have received the full-day Laser Safety Training course. The hazards pertaining to the
apparatus as well as safety precautions and operating procedures (extracted from the course) that must
be obeyed are clearly outlined (Tr3).
4.1.2 – Laser Safety Quiz
The purpose of the laser safety quiz is to ensure that the student is familiar with the safety procedures
associated with the apparatus prior to commencing the lab (refer to Appendix E). The quiz is based on
the lecture presentation that is delivered to the student by the TA prior to beginning the experiment,
and the content is derived from the full day Laser Safety Training course offered at U of T.
The quiz serves to test the student’s comprehension of the material presented, rather than
memorization of details and regurgitation of information. For instance, true/false questions test for
lower-order outcomes and can be based on either misconceptions or cause-effect reactions[H3][H5].
This was utilized to test the student’s knowledge of the danger associated with beam alignment.
Multiple choice questions test for higher-order outcomes, such as analysis and synthesis of information.
Short answer questions test the ability of the student to synthesize, analyze and apply the information
presented while minimizing guessing. It is modeled after the safety quiz given to students at the end of
the course as well as Laser Safety Quizzes used at other universities, such as the University of California
– Berkeley [H1]. Various university teaching resources and guidelines for designing the questions were
consulted to design for clarity and testing for comprehension [H3][H4]. It encompasses the safety
procedures to be followed, the hazards associated with the laboratory and apparatus, prevention of
hazards and the specific characteristics of the laser, which were the main areas of emphasis in the Laser
Safety Training course. The time allotted for the quiz will be 15 minutes, which was determined to be
sufficient based on the Experiment Demonstration. The student is expected to convey their
understanding and must receive above 80% to pass the quiz and proceed with the experiment. Any
questions that the student did not answer correctly must be discussed with the TA/Instructor prior to
beginning the lab. This will ensure that the student has a thorough understanding of the expectations,
procedures and the apparatus, and is capable of safely carrying out the experiment.
4.1.3 – Pre-lab Exercise
13
APL experiment manuals typically [H2] do not contain pre-lab questions. However, it was determined
that a pre-lab exercise which entails outlining the path of the laser beam for the Optical Tweezers is
necessary. As this apparatus employs a high-powered laser, it is crucial that students are aware of the
laser beam path, which could reduce the risk of accidents [Sandu Sonoc, Laser Safety Training course,
UofT]. The TA will be expected to walk through the path of the laser and indicate the critical
components of the apparatus.
4.1.4 – Safety Sheet
Clear and succinct safety instructions are displayed on the wall near the apparatus to inform students of
the procedure that must be followed prior to beginning the experiment (EP1). These include ensuring
that the “Laser Work in Progress” sign is placed on the door to inform others, emphasizes that safety
glasses must be worn at all times, and provides emergency contact information in the case of an
accident (E2-E6) (Appendix C). These standard operating procedures (SOPs) that must be obeyed when
working with lasers were obtained from the Laser Safety manual provided by the Office of
Environmental Health and Safety at the University of Toronto. The SOPs are also stated in the lab
manual, though having them mounted on the wall provides an additional level of safety in case the
student skips to the beginning of the experiment section.
4.2 – Experimental Procedure
For the experimental procedure, revision of the existing student manual as well as the creation of a TA
manual took place, with a focus on the Equipartition experiment. The main downfalls of the existing
manual are outlined in Figure H3. The following sections discuss in detail the revision process and
development of a reliable student manual containing sufficient details, safety precautions and
presented in a well-organized, logical and cohesive manner. As well, the process of creation of a TA
manual and determination of necessary sections is also outlined.
Figure H3: The transformation of the existing experiment manual into an improved student manual which addresses the
limitations and the creation of a TA manual.
4.2.1 – Student Manual
4.2.1.1 – Lab Structure and Organization
The existing lab manual began with the Introduction, Theory, and a general description of the various
experiments. However, important details such as how to perform the lab, a description of the
components and data collection were located in the appendices.
14
The revised lab manual was restructured in chronological fashion (Figure H4) with numbered steps
within sub-sections rather than a large paragraph or bulleted form. This provides a logical progression of
steps required to carry out the experiments in a digestible format. The Introduction and Theory (EP5) is
followed by a description of the numerous components of the Apparatus such that the student can
become familiar with these prior to beginning the experiment. The Pre-Lab exercise is placed after the
Apparatus section, as the previous section aids in answering the pre-lab question. Next, the Laser Safety
section is presented to familiarize students with the safety procedures prior to beginning the
experiment. The following section states the experimental procedure for the Equipartition experiment,
and includes all the necessary information (sample preparation, laser diode controller settings, bead
trapping and data acquisition) in the order that the student is expected to carry out the various steps.
The subsequent sections describe additional experiments that can be performed to calculate the trap
stiffness in the following laboratory sessions. The experimental procedure is proceeded by details
surrounding Post-Lab Questions, Data Analysis and Student Assessment. Finally, the Appendices include
additional resources that the student may wish to consult. For example, the manufacturer’s manuals
and relevant research papers on optical tweezers are included, which may assist in understanding the
theory and equipment. The student manual can be found in Appendix B.
Figure H4: The organization of the revised Student Manual in chronological order.
4.2.1.2 – Procedure Development
For the development of the student manual, several procedural considerations had to be taken into
account. The requirements necessitated the inclusion of additional sections, such as one devoted to
laser safety (EP1), and more detailed procedural steps to facilitate the execution of the experiment
(EP2). The revision process consisted of the following main components that were employed in order to
devise a reliable, safe, and reproducible protocol for student use (Figure H1).
Figure H1: Process used to verify the existing protocol and develop a reliable student manual.



Execution of existing lab: The existing lab was attempted in order to determine whether a student
would be able to carry out the numerous optical trapping experiments solely through the lab
manual provided.
Identifying missing components and issues: Execution of the existing lab revealed countless
procedural details that were excluded, unclear, or incorrect. For instance, certain settings for the
laser diode controller indicated in the manual were inaccurate and well above the maximum output
range of the controller. As well, procedural details such as how to power the LED light in order to
illuminate the sample such that it can be imaged through the camera and proper placement of the
sample slide into the holder were omitted. Further, a laser safety section including the hazards and
hazards control was absent from the manual.
Research similar protocol: To develop the missing procedural details, research of sample protocols
that involved Optical Trapping through Equipartition and employed a similar apparatus was carried
out.
15




Consultation with resources: The protocol was further developed following a walk-through of the
experiment with the student who had created the existing lab manual (Jimmy Shen). This walkthough revealed additional details that were critical in the execution of the experiment.
Establishment of procedure: A complete and thorough procedure was established by including the
details retrieved from sample protocols and those discovered during the walk-through of the
experiment.
Verification of procedure: Procedural details were verified against the various manuals for the
Optical Tweezers apparatus provided by Thorlabs. For instance, the maximum current limit was
obtained from the Laser Diode manual [H6], and temperature control ranges were obtained from
the ITC Laser Diode Combi Controller Manual [H7].
Refinement of procedure: The experiment was executed following the redeveloped manual to
verify the organization and determine whether any details were still absent. This run-through
exposed several issues pertaining to organization of the steps, which were addressed to further
develop the protocol. In addition, further experimentation was necessary to develop values such as
a preferred dilution to be used for the sample, as this affects the quality of the data.
The above process led to a complete manual with adequate and accurate procedural details to facilitate
execution of the Equipartition experiment. However, the inclusion and exclusion of specific
sections/details had to be considered next.
4.2.1.2.1 – Inclusion of Sections
Numerous sections and additional details/figures were incorporated into the existing lab manual:
 Safety Considerations: The requirements indicated that safety instructions be presented through
the experimental write-up (EP1). A section was devoted to Laser Safety, and included the main
topics from the Laser Safety Training course and manual as well as additional details pertaining to
the Optical Tweezers. The characteristics of the laser, the associated hazards, and hazards control
were included before the experimental procedure, to ensure that the student is well aware of the
safety precautions that must be obeyed. As well, additional security measures were also embedded
into the procedural details. For instance, the laser controller key must be obtained from Rob
Smidrovskis when performing the experiment, and must be returned at the end of the laboratory
session (E6). A schematic of the Laser Diode Combi Controller that was present in existing lab was
modified to highlight key features such as the Laser on/off button, as this must be immediately
powered off if someone enters the room (EP5).
 Applications: A section that briefly discusses relevant applications of the Optical Tweezers is
presented in order to bridge the gap to current research, which serves to fulfill one of the goals of
the Advanced Physics Laboratories [H8].
 Extension to experiments:
As the existing lab manual made no mention of the properties of the beads, the experiment was
tested with varying bead diameters of polystyrene beads. Beads of diameter ranging from under
1μm to slightly above 1μm have been made available for students to experiment with. This will
allow the identification of the differences in trap stiffness that arise when the properties of the bead
are varied.
 Relevant websites: A list of helpful websites are stated in the appendices to provide additional
resources that the student can consult, as this was deemed crucial during the experiment trials. For
instance, the Thorlabs’ manuals and relevant research papers are included that may assist the
student in better understanding the laboratory concepts, the equipment and the applications (EP6).
16


Figures: Certain figures were included to provide greater clarity regarding the procedure. A
schematic of the sample slide was added to demonstrate the numerous layers that must be added
to the slide (double-sided tape, cover slip, grease, etc.), which are not apparent in the diagram
within the existing manual. This was included to add clarity, as proper sample preparation is
essential for successful execution of the experiment. As well, some figures were included to indicate
the location of certain components of the apparatus, such as the objective lens on top of which oil
must be added, as this is a crucial step without which the experiment would not function. Finally,
the overall apparatus and a schematic representation have been included in the manual to provide
students with two different perspectives regarding the operation of the optical trapping
equipment. Students more visually inclined can compare the physical apparatus to the labeled
photographs, while students more theoretical in nature can use the ray diagram to comprehend the
path of the laser. Both methods will aid in the understanding of how the apparatus operates.
Additional procedural details: The inclusion of a detailed operating procedure was incorporated for
critical sections, such as the settings for the Laser Diode Controller. Although APL labs are not
traditionally structured in this way, this method of providing detailed standard operating procedures
was enforced by Sandu Sonoc during the Laser Safety Training. It is expected to help alleviate
potential accidents if proper procedures are included for parts of the lab that are susceptible to
error (EP2).
4.2.1.2.2 – Exclusion of Sections
Numerous sections and details were excluded from the complete manual that was created:
 Increasing safety:
Procedural steps that were prone to erroneous conduct were left for the TA manual, as this enabled
the implementation of greater security measures. For example, setting the maximum current of the
laser diode using the screwdriver-potentiometer is left for the TA, as the current can be increased
significantly beyond what is required.
 Open-ended experimentation:
Although detailed steps were included for susceptible portions of the lab, sections that were carried
out following the implementation of the safety measures were left open-ended, so as to allow the
student to explore the apparatus and discover the details individually. For instance, several hints are
provided for viewing the bead sample and optical trapping. Since the enclosures are in place and the
maximum current limit has already been preset and cannot be altered by the student (without a
screwdriver), the apparatus is sufficiently safe for individual exploration. This is in accordance with
the APL goals, which place an emphasis on self-discovery and a focus on instrumentation [H8]. The
TA is also available for further assistance if necessary.
4.2.1.3 – Sequencing of Sub-Experiments
The lab consists of three sub-experiments -- Equipartition, Stokes’ Drag and Power Spectrum – which are
to be executed within 18 hours over the course of three weeks (E1, EP3). The Equipartition experiment
through the CCD camera is placed first as it is the most straight-forward among the three, and will
enable the student to become acquainted with the apparatus, safety precautions and the procedure for
trapping a bead. The more challenging experiments that utilize additional components of the Optical
Tweezers are left for the subsequent experiments as the student will already be familiar with the
apparatus and software tools. The Stokes’ Drag and Power Spectrum experiments along with an
alternative method for data collection (using the Quadrant Photo-Diode) are to be executed in the
following lab sessions.
17
4.2.2 – TA/Instructor Manual
The TA manual consists of a complete detailed experimental protocol for the TA or Instructor such that
they are capable of assisting students when necessary (EP4) (Appendix C.2). TAs are provided with:
 Screen shots of certain steps (eg. An image of a trapped bead, a sample slide for which the solution
has leaked from the channel)
 Hints for difficult steps (eg. Trouble-shooting when the beads cannot be seen through the camera)
 Assembly and disassembly procedures of the enclosures: this is to be performed by the
TA/Instructor only, and detailed instructions for how to dismantle the enclosures including images
of each step have been added (Tr4).
 The beam alignment procedure and best practices: details on performing beam alignment (should
the need arise) are included as per the University of Toronto’s Environment Health and Safety
website. This is strictly for the TA/Instructor who is certified in Laser Safety, as students are not
permitted to perform beam alignment since they have not received the full Laser Safety Training.
 Indicators of certain points in the lab during which extra caution must be exercised: For instance,
when the students are attempting to adjust the micrometers and are unable to view the beads, they
may be inclined to remove their glasses. TAs are made aware of this and are instructed to
emphasize that safety glasses must be worn at all times.
The above should allow the TA to carry out the Equipartition experiment with ease and provide the
necessary support to students as they are performing the lab.
4.3 – Post-Experiment
Post-experiment considerations include student assessment and the associated mark break-down.
4.3.1 – Student Assessment
The student mark break-down is based on the patterns of marking followed in the APL, as well as some
additional components that were included [M1]. The mark allocation for student work for the Optical
Tweezers experiment is listed below:
Table M1 The Mark Break-Down for the Optical Tweezers Experiment
Category
Pre-lab
Notebook
Calculation of Trap Stiffness (Excel/Matlab)
Post-lab discussion with TA / Professor
100% on Laser Safety Quiz
Percent Composition
3%
17%
40%
40%
2% (bonus)
18





Notebook: A notebook should be kept throughout the labs to keep a record of all activities
undertaken. This notebook is to be brought in with the students on the day of their oral
examination. The post-lab questions must be must be answered in the notebook with any additional
Excel/Matlab based calculations printed and attached. The post-lab questions are more general in
nature, and include theoretical questions, equipment related questions and observational based
questions. This ensures that the student’s general understanding of the theory and the methods is
assessed, and that the lab is not completely data-driven (SA1). As well, the informal write-up should
include a brief discussion of a research paper that utilizes Optical Tweezers (SA3).
Post-lab discussion with TA/Professor: In accordance with the existing APL structure, an oral
examination an oral examination will take place following the final laboratory session (SA1). The oral
exam will be 25 minutes long. There will be three examiners, all of whom are either professors or
demonstrators in the course, and at least one of the three examiners will be a professor. The
student must bring their experiment notebook to the examination, which will follow the APL Oral
Exam guidelines. It will take place after two weeks following the completion of the last session of
the lab to provide adequate time for the students to complete the lab write-up (SA2).
Calculation of Trap Stiffness: Calculation of trap stiffness will involve processing the data through
matlab files and using the equations provided in the lab manual. The value of trap stiffness among
the various sub-experiments and varying bead diameters should be compared and contrasted.
Pre-lab: Although APL labs typically do not have a pre-lab exercise, the pre-lab question added to
the Optical Tweezers experiment serves to raise awareness of the laser beam path as previously
mentioned.
Laser Safety Quiz: The student can earn a 2% bonus by receiving 100% on the safety quiz given prior
to the experiment. This is to provide further incentive to the student to pay close attention to the
safety requirements, hence leading to a safer working environment.
4.4 – Demonstration
The experiment walk-through was critical in determining the quality of the student manual in terms of
clarity and its effectiveness in delivering the procedural details accurately. The walk-through revealed
that the lab could be executed in a safe and secure manner with the safety instructions provided by the
TA/lab manual and with the interlock and enclosures in place. It also revealed that the student required
minimal initial training in order to perform the lab, which fulfills the student training criteria (Tr2).
However, numerous areas of improvement were identified through the experiment demonstration, such
as some minor issues with the sequencing of certain steps for sample preparation, ambiguity in the
diagram for the sample slide, and an additional figure that could be included for further clarification.
These points were addressed and an updated student manual can be found in Appendix B. In addition,
certain portions of the experiment required self-discovery through experimentation with the apparatus.
These details have been left out of the student manual, as the students are expected to explore the
instrumentation on their own and establish the missing steps. Finally, it was determined that a particular
quiz question (#5b) was misunderstood by both “students”. As such, the question was posed with
greater clarity and better word choice in the updated quiz (Appendix E) based on the feedback received.
4.5 – Experiment Budgetary Analysis
The following materials are required for the experiment: microscope slide, cover slip, double-sided tape,
P200 micropipette, pipette tips, kim wipes, razor blade, vacuum grease, distilled water and eppendorf
tubes. These are available for use in the Physics Department, and did not have to be purchased. Stock
19
solutions of polystyrene beads with varying diameters (slightly less than and greater than 1μm) were
provided by Daniel Faulkner (MSE Department) and are available for future use for the experiment. As
such, no expenditures took place for the experimental portion of the design.
4.6 – Future Work
For the Optical Tweezers’ experimental protocol to be completed, the remainder of the subexperiments must be run. This includes Stokes’ Drag, Power Spectrum, and optical trapping through the
quadrant photo-diode. Once this occurs, a more detailed procedure for these sections can be
developed. This can be accomplished through a summer student, and would lead to a complete
laboratory manual for student use.
6. OVERALL FUTURE WORK AND CONSIDERATIONS
In order to successfully integrate the Optical Tweezers experiment into the Advanced Physics
Laboratories, additional work must still be completed. These tasks have not yet been accomplished due
to focus on meeting client requirements that the apparatus first and foremost be safe for untrained
student use. Now that the protective enclosure and interlock system have been implemented, the
equipment is safe for use and focus towards the experiment can continue. Key tasks which must be
undertaken include:
 The various LabView files required for controlling the Piezo Controller (necessary for performing
the QPD experiment) and other Matlab files that are needed to analyze data must be retrieved
from Jimmy Shen or from Professor Ryu’s lab.
 The enclosure and interlock system should be revisited by Dr. Sandu Sonoc in order to approve
the Optical Tweezers apparatus as a Class 1 Working Environment.
 Involvement of Natalia Krasnopolskaia (Physics Lab Coordinator) is required to provide further
input as to the necessary steps prior to the experiment being launched.
 Incorporation of the client’s proposed modifications and improvements to the student manual.
 Have a group of Physics students test out the various experiments, analyze the data collected
and determine the trap stiffness. This will provide the TA with reference material for marking.
The above steps can be carried out by students who will be involved in design projects in the upcoming
Winter 2011 semester. For further information, please refer to Appendix L.
7. CONCLUSION
This design report outlines the details of the enclosed beam and interlock solution implemented to
ensure that the Optical Tweezers apparatus in the Advanced Physics Laboratory at the University of
Toronto is safe for untrained undergraduate student use. By encasing the 330mW trapping beam in a
protective enclosure and developing an interlock system to ensure that the beam immediately turns and
remains off when the enclosure is removed, our solution guarantees the safety of inexperienced
students using this apparatus. This enclosure and interlock system has been developed to meet the
precise requirements, criteria, and constraints established in consultation with Professor David Bailey
and Dr. Sandu Sonoc.
Through the implementation of this design, the optical tweezers equipment is secure and students will
now be able to complete the experiment detailed in this report and determine the stiffness of various
optical traps. Students will be provided with detailed safety instructions and complete a safety test
20
before beginning to work on the lab, and so will then be able to explore optical trapping freely,
according to their individual learning styles.
21
8. REFERENCES
[S1] Shaevitz, Joshua W. “A Practical Guide to Optical Trapping.” Berkeley, 2006.
[S2] Bailey, David. “Advanced Physics Laboratory Course Outline.” University of Toronto Physics
Department, Toronto, 2010.
http://www.physics.utoronto.ca/~phy326/course%20outline%20fall%2010.pdf
[S3] “An Overview of the LED and Laser Classification System in EN 60825-1 and IEC 60825-1.” Lasermet
Ltd. http://www.lasermet.com/resources/classification_overview.php
[S4] “Optical Trapping Kit.” Thorlabs.
http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=3959
[S5] Neuman KC, Block SM (2004). "Optical trapping". Review of Scientific Instruments 75 (9): 2787–
2809.
[S6] Donald Norman: Invisible Computer: Why Good Products Can Fail, the Personal Computer Is So
Complex and Information Appliances Are the Solution. MIT Press. 1999.
[S7] Kolb, David (1984). Experiential learning: Experience as the source of learning and development.
Englewood Cliffs, NJ: Prentice-Hall.
[L1] Optical Trap Application Setup. Thorlabs, Inc. http://www.thorlabs.com/Thorcat/19500/19590M01.pdf
[L2] LANshack.com [Online], Available: http://www.lanshack.com/fiber-optic-tutorial-cable.aspx
[L3] Don’t Ignore the Hazards Associated with Fiber Optics. EC&M. Available:
http://ecmweb.com/mag/electric_dont_ignore_hazards/
[L4] laser Safety. http://en.wikipedia.org/wiki/Laser_safety#Class_1
[L5] University of Toronto Environmental Health and Safety [Online], Available:
http://www.ehs.utoronto.ca/services/laserpg/laserhome.htm
[L6] Plastic World. http://www.plasticworld.ca/default.asp?pID=7
[L7] 2 In. Zinc Plated(2c) Corner Brace. Home Depot.
http://www.homedepot.ca/webapp/wcs/stores/servlet/CatalogSearchResultView?D=948074&Ntt=9480
74&catalogId=10051&langId=15&storeId=10051&Dx=mode+matchallpartial&Ntx=mode+matchall&N=0&Ntk=P_PartNumber
[L8] E-6000 Industrial Strength Adhesive, http://www.biosafe-inc.com/e6000_ind.htm
[L9] LM14S2 Butterfly Laser Diode Mount Operating Manual
http://www.thorlabs.com/THorcat/10600/10614-D02.pdf
[L10] The Source. http://www.thesource.ca/estore/default.aspx?language=en-CA
[L11] Creatron Inc.. http://creatroninc.com/
[L12] “Plastic Laser Filter Windows.” Lasermet. http://www.lasermet.com/filter-windows-plastic.php
22
[H1] Laser Safety Training Quiz, University of California – Berkeley:
http://labs.physics.berkeley.edu/mediawiki/images/3/3e/L111LaserSafetyQuiz4-1-08.pdf
[H2] Advanced Physics Laboratory - Experiment List, University of Toronto:
http://www.physics.utoronto.ca/~phy326/explist.htm
[H3] K.I. Adsit, “Designing Test Questions”, The University of Tennessee at Chattanooga. 2003. [Online]. Available:
http://www.utc.edu/Administration/WalkerTeachingResourceCenter/FacultyDevelopment/Assessment/testquestions.html
[H4] J, Murdock, “Basic Tips for Writing Effective Multiple Choice Questions”, Department of Economics, UofT, July
2006.
http://homes.chass.utoronto.ca/~murdockj/teaching/MCQ_basic_tips.pdf
[H5] Designing Effective Quizzes, Adobe Systems Inc. 2010.
http://www.adobe.com/education/resources/hed/instructional/connect/collaborative_teaching/pdfs/designing_q
uizzes.pdf
[H6] Pigtailed Laser Diode, Thorlabs:
http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=4190&Guide=127&Category_ID=94
[H7] ITC510 Laser Diode Combi Controller:
http://www.thorlabs.com/thorcat/7100/7111-D02.pdf
[H8] Engineering Academic Calendar 2010-2011, University of Toronto:
http://www.undergrad.engineering.utoronto.ca/Assets/UndergradEng+Digital+Assets/calendar
1011/Chapter+8.pdf
[M1] Advanced Physics Laboratory course outline, September 2010
http://www.physics.utoronto.ca/~phy326/course%20outline%20fall%2010.pdf
23
APPENDIX A – Requirements, Constraints and Criteria
The following are the Technical Constraints (Table A1), Experimental Constraints (Table A2),
Student Assessment Criteria (Table A3), Experimental Protocol Criteria (Table A4), and Training Criteria
(Table A5) for Optical Tweezers Experiment that were presented in the Preliminary Design Report.
These were developed in consultation with Professor Bailey (coordinator of the Advanced
Physics Laboratory), Professor Ryu (Professor in the Department of Physics), and Dr. Sandu Sonoc
(Certified Laser Safety Officer, Radiation Protection Service).
Table A1 Technical Constraints
Item
ID
T1
T2
T3
T4
T5
T6
T7
Description of Constraint
The Optical Tweezers experiment must be made safe for undergraduate students who have not
taken the full day laser safety course and should be classified as a Class 1 laser.
The optical tweezers system employs a 980nm laser with a maximum power output of 330mW.
If the laser is exposed, it is considered a Class 3B laser. Appropriate measures must be taken to
enclose the optical path of the beam at the region where the laser is exposed. If the enclosure
is opened for beam alignment, the laser power output must be reduced to 5mW (Class 1) or
the laser must be completely shut off.
The light path where the beam is exposed to air should be enclosed.
The fibre optic should be enclosed for protective purposes. It would be helpful to be able to
observe the fibre optic under the enclosure.
The reflected beam should not leak out from the sample stage, and the user must be able to
move the sample stage using the knobs (Refer to #7 in Figure 1).
There are x, y, and z knobs for sample stage movement. These must be accessible when the
beam is on.
Budgetary constraints: Additional components added onto the existing apparatus should not
exceed CDN $1000.
The design must prevent students from inserting an object into the path of the laser which
could cause the beam to diverge.
Interlocks should not automatically reset. If an interlock is opened and the beam is turned off,
the beam should not turn back on automatically when the interlock is closed again; the laser
should need to be turned back on.
Table A2 Experimental Constraints
Item Description of Constraint
ID
E1
The experimental procedure should be executed within 18 hours over the course of 3 weeks.
Advanced Physics Laboratory structure.
E2
The room door must be closed and locked with a temporary “Laser Work in Progress” sign placed
outside the room door.
This sign can be provided by Sandu Sonoc, the Senior Radiation Safety Officer.
E3
Appropriate laser safety glasses must be worn at all times when using the equipment.
E4
The beam will not be pre-aligned prior to the student commencing the lab.
E5
The beam should be turned off when changing samples.
24
E6
E7
Changing the sample involves moving somewhat reflective material in and out of the beam path.
The beam must be turned off when this occurs. Normally, no light should reflect out when
changing the sample, but there is a chance that if someone sticks something in (eg. A pen to
indicate the beam position), then inserting an object may cause the beam to reflect wildly.
The laser power supply key should be kept by the technologist.
The experiment should be carried out individually, in accordance with APL structure.
Table A3 Student Assessment Criteria
Item Description of Criteria
ID
SA1 The mark composition for the laboratory should not be completely data-driven, and should
include a combination of data analysis within the student’s lab notebook as well as more general
questions pertaining to the lab that assess the student’s understanding. It should also include a
discussion with the TA/Professor regarding the results obtained.
This is in accordance with APL structure, and the consultation with the TA/Professor would
enhance oral and written communicability of technical material [6].
SA2 Adequate time must be provided to the student for completion of the lab write-up.
SA3 The write-up should include a brief discussion of a research paper that utilizes Optical Tweezers
to bridge the experiment to current experimental research [5].
Table A4 Experimental Protocol Criteria
Item Description of Criteria
ID
EP1 Clear and succinct safety instructions must be given to the students through the experimental
write-up, from the instructor, and displayed on the wall near the equipment.
EP2 The experiment should provide more detailed procedural steps to facilitate the execution of the
experiment. This will ensure that a proper procedure is followed and leaves less room for
erroneous conduct around a high-powered laser.
EP3 The entire experiment should be divided into sections or a series of experiments that investigate
different concepts such that they can be carried out over the course of the 3-week lab.
The experiment should not be repetitive or tedious.
EP4 A more detailed experimental protocol should be provided to the TA/Professor to enable them to
assist the students when necessary. This should detail the potential pitfalls that may be
encountered [7].
EP5 The protocol should include the background and theory pertaining to the lab, as well as clearly
detailed schematics of the apparatus [7].
EP6 A list of relevant websites and papers that will aid the student in understanding the laboratory
concepts or equipment should be included.
EP7 The experiment should incorporate a variety of skills and techniques [7].
Table A5 Training Criteria
Item
ID
Tr1
Tr2
Description of Criteria
The TA/Professor present during the laboratory session should be well acquainted with the
experimental procedure and apparatus and should be available for assistance.
The student must require minimal initial training in order to execute the lab.
25
Tr3
Tr4
Tr5
An introduction to the lab should be given by the TA/Professor to acquaint the student with
the lab concepts, the equipment, expectations and clearly stated safety instructions.
An instructor/TA manual should be provided, which includes additional details such as
information on the safety features and disassembling enclosures.
The TA supervising the experiment must attend the full day Laser Safety Training course.
26
APPENDIX B – Design Drawings of Open Beam Enclosure
The following are the drawings submitted to the Physics Machine Shop for the fabrication of the Open
Beam Enclosure.
27
COMPONENT 1 – BACK OF ENCLOSURE
COMPONENT 2 – SIDE OF ENCLOSURE
COMPONENT 3 – FRONT OF ENCLOSURE
COMPONENT 4 – SIDE OF ENCLOSURE
COMPONENT 5 (NOT SHOWN) – TOP OF
ENCLOSURE
OPEN BEAM ENCLOSURE – OVERALL
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
28
SHEET 1 OF 6
OPEN BEAM ENCLOSURE – COMPONENT 1 (BACK OF ENCLOSURE)
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
29
SHEET 2 OF 6
OPEN BEAM ENCLOSURE – COMPONENT 2 (SIDE OF ENCLOSURE)
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
30
SHEET 3 OF 6
OPEN BEAM ENCLOSURE – COMPONENT 3 (FRONT OF ENCLOSURE)
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
31
SHEET 4 OF 6
OPEN BEAM ENCLOSURE – COMPONENT 4 (SIDE OF ENCLOSURE)
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
32
SHEET 5 OF 6
OPEN BEAM ENCLOSURE – COMPONENT 5 (TOP OF ENCLOSURE)
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
33
SHEET 6 OF 6
APPENDIX C – Design Drawings of Optical Fiber Enclosure
The following are the drawings submitted to the Physics Machine Shop for the fabrication of the Optical
Fiber Enclosure.
34
OPTICAL FIBER ENCLOSURE – OVERALL
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
35
SHEET 1 OF 9
OPTICAL FIBER ENCLOSURE – CROSS SECTION OF ENCLOSURE
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
36
SHEET 2 OF 9
OPTICAL FIBER ENCLOSURE - TOP
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
37
SHEET 3 OF 9
OPTICAL FIBER ENCLOSURE – COMPONENT 1
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
38
SHEET 4 OF 9
OPTICAL FIBER ENCLOSURE – COMPONENT 2
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
39
SHEET 5 OF 9
OPTICAL FIBER ENCLOSURE – COMPONENT 3
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
40
SHEET 6 OF 9
OPTICAL FIBER ENCLOSURE – COMPONENT 4
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
41
SHEET 7 OF 9
OPTICAL FIBER ENCLOSURE – COMPONENT 5
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
42
SHEET 8 OF 9
OPTICAL FIBER ENCLOSURE – COMPONENT 6
UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES
43
SHEET 9 OF 9
APPENDIX D – Total Cost of Safety Enclosures and Interlock
The following outlines the costs associated with the fabrication and installation of the safety enclosures
and interlock.
Table D1 Total Cost of Safety Enclosures and Interlock
Amount
Required
Unit Price
Total Cost
(incl. taxes)
Vendor
1
6.99
$7.90
The Source
5 ft
$1/ft
$5.00
Creatron Inc.
N/A (already
have this)
N/A
N/A
N/A
5
$0.70
$3.50
Creatron Inc.
1 ft2
$9.00/ft2
$10.17
Plastic World
Off-cuts
(2 pieces)
$12.00
$13.56
Plastic World
E6000 Industrial
Strength Glue
110mL
$8.95
$10.11
Plastic World
2 In. Zinc Plated
Corner Brace
(Stanley)
9
$1.49
$15.15
Home Depot
Bolts
9
$0.50
$5.09
Home Depot
10 hrs
$25/hr
$250
Department of
Physics
Machine Shop
Total Cost:
$320.48
Component
Item
Safety Interlock
2.5 mono phono
jack
Wire
Solder and Soldering
Iron
Microswitches
Safety
Enclosures
Opaque Acrylic (1/4”
thickness)
Transparent Acrylic
(1/4” thickness)
Labour
44
APPENDIX E –Alternative Laser Safety Solutions
Each of the alternative laser safety solutions consists of two components: making the laser safe for
students to use and also assuring that the laser itself is protected while in use.
In order to protect the laser, it is necessary to enclose the Optical Fiber that connects the output of the
laser diode to the FiberPort component of the apparatus that collimates the laser beam. Each of the
alternative solutions includes an enclosure for the Optical Fiber.
Alternative Solution #1
Electromechanical: Control of laser depending on enclosure state (open/closed)
It is one of our goals to make the laser safe for students by limiting the amount of power going through
the laser after it has gone through Fiber Controlled Laser Source (component 1 in Figure 1b and the fiber
optic wire. This can be done by inserting an optical density filter between the Fiber Port Collimator (part
2 in Figure 1b) and the Beam Expander (part 3 in Figure 1b). The optical density filter would reduce the
power of the laser beam to the desired 5mW. This filter can be purchased from Thorlabs and mounted
on the laser using the Magnetic Mount already available to us.
It is required by our clients that the students should not be able to open the enclosure around parts 1
and 2 when the laser is on and the power through the laser is more than 5mW. In order to address this,
we would attach a touch sensor plan on top of the magnetic mount of the filter that will be turned on
when the box is closed. The output of this touch sensor is input to an external control button. This
control button will allow students to open the enclosure when the laser is on. For example, if the box is
closed, the laser is on, and the magnetic mount is not inserted, the touch sensor will open the control
button’s circuit and the latch that is controlled by the button will not work.
Figure A1shows a rough schematic that demonstrates the connections:
Figure A1 Block diagram of the laser enclosure, the magnetic mount, and connection to the touch sensor and control button
45
Figure A2 demonstrates how the latch is controlled by the touch sensor:
Figure A2 Control of Latch using Touch Sensor
The addition of the enclosure to the pre-existing apparatus is estimated to be about CDN $100, including
the material and the latch. Since the magnetic mount has already been purchased, it will not be an
additional cost. The sensor is priced at about CDN $50 on the Thorlabs website, and other parts that
may need to be purchased (including circuit components, the control button, etc.) will cost about CDN
$200. We estimate the total cost to be about CDN $500, which meets the budgetary constraints of CDN
$1000.
Alternative Solution #2
Microcontroller: Control of laser depending on enclosure state (open/closed)
Another method of controlling the laser power output would be through a microcontroller design. The
controller (ITC510) would be interfaced with the IEEE488 that is based on the IEEE488.2 standard. This
includes the IEEE488.1 standard for the hardware settings. This interface can be used to control whether
the laser is on or off by taking advantage of built in hard codes that can control the operation status of
the laser.
The microcontroller device would be controlled based on an electrical connection made when a
magnetically-mounted optical density filter (described in Potential Solution #1) is inserted in the laser
pathway. When the optical density filter is inserted in front of the laser, the microcontroller receives the
positive signal that the laser is safe. This would allow the laser to operate at its maximum power. If the
mount is removed while the laser is in “on” mode at full power, a negative signal will be sent through
the connection to the microcontroller which will result in a reduction of power or shut off the laser
completely. Through this direct control of the state of the laser through the microcontroller, the
experiment would be considered laser safe as the laser would be turned off in appropriate
circumstances.
As in Proposed Solution #1, the addition of the enclosure to the pre-existing apparatus is estimated to
be about CDN $100, including materials and fabrication. The cost of the microcontroller is estimated to
be CDN $100, with additional electrical components costing another CDN $50. This brings the total cost
of this proposed solution to CDN $250, which is within our budgetary constraints.
Alternative Solution #3
Mechanical: Control of laser depending on enclosure state (open/closed)
A third possible solution for ensuring the safety of the users from the laser depending on the enclosure
state is to use an enclosure that consists of two components: 1) A left half of box which would be fully
46
enclosed with plexiglass, and 2) A right half which consists of an optical filter and is not enclosed at the
top (A3). These two components would be connected and placed on a track, which would allow
movement of the box along the track. When the experiment is in operation once the beam has been
aligned, component 1 would be in front of the beam as it is a fully enclosed box. It would protect laser
beam from being exposed to the human eye and causing harmful effects, as it will be operating at full
power (330mW). When the laser beam alignment takes place, the box must be slid along the track so as
to place component 2 in front of the beam. This component would filter the high power beam and
enable the student to safely perform beam alignment. The exposed top would allow appropriate access
to the apparatus once the filter reduces the power of the beam to the acceptable value of 5mW. Thus,
while the experiment is being carried out, the enclosed box would prevent exposure to the beam, and
while beam alignment is taking place, the optical filter will reduce the laser beam power. This would
enable the re-classification of the system to a Class 1 Laser. In addition, to prevent foul play, the entire
enclosure will slide along a T-Track which will include barriers at either end. This physically prevents the
box from being removed from the track and disables students from fiddling with the proposed interlock
system, ensuring their safety at all times (Figure A3).
The addition of the multi-component enclosure to the pre-existing apparatus is estimated to be about
CDN $250, including materials for the plexiglass and tracks, as well as fabrication of the unique design.
The cost of the optical density filter is estimated to be CDN $50. This brings the total cost of this
proposed solution to CDN $300, which is within our budgetary constraints.
Figure A3 Design of Proposed Solution #3; Mechanical Solution with 1) Fully enclosed plexiglass component, and 2) Optical
filter component
47
Assessment of Implemented and Alternative Solutions
Table E1 provides an assessment of the implemented and alternative solutions with respect to the
technical constraints defined during the preliminary design stages of the project.
Table E1 Comparison and Assessment of Implemented and Alternative Solutions
Constraint
Implemented
Solution
Alternative
Solution #1
Alternative
Solution #2
Alternative
Solution #3
T1: Enable apparatus
to be classified as
Class I




T2: Exposed laser
beam is enclosed

X Uses a magnetic
mount to reduce
laser power when
laser is on, but
does not prevent
access to laser
beam
X Uses a magnetic
mount to reduce
laser power when
laser is on, but
does not prevent
access to laser
beam
X Uses a magnetic
mount to reduce
laser power when
laser is on, but
does not prevent
access to laser
beam
T3: Fiber optic is
enclosed




T4: Maintain ability
to move sample stage




T5: Within budgetary
constraints




T6: Prevents students
from accessing
exposed beam

X Uses a magnetic
mount to reduce
laser power when
laser is on, but
does not prevent
access to laser
beam
X Uses a magnetic
mount to reduce
laser power when
laser is on, but
does not prevent
access to laser
beam
X Uses a magnetic
mount to reduce
laser power when
laser is on, but
does not prevent
access to laser
beam
48
APPENDIX F – Student Manual
<<END OF APPENDIX F – STUDENT MANUAL>>
APPENDIX G – Teaching Assistant/Instructor Materials
G.1 – Pre-Experiment Presentation
G.2 – Teaching Assistant Manual
<<END OF APPENDIX G.2 – TA MANUAL>>
G.3 – Pre-Lab Exercise
1. Path of the laser leading upto the sample:
49
a. The trapping source is a temperature stabilized 330mW (max) fiber pigtailed laser diode
which has a central wavelength of 980nm. It has a TEC element that stabilizes the
temperature of the diode to prevent power fluctuations.
b. The laser is transported through the fibre optic wire.
c. The FiberPort collimates the trapping laser (light rays are almost parallel).
d. Next, the beam passes through the Beam Steering Mirror.
e. Two relay lenses expand the trapping laser beam so that it fills the back aperature of the
focussing objective. The second lens images the sample onto the CCD Imaging Detector.
f. The dichroic mirror reflects 980nm light into
the vertical path, where a 100X oil
immersion Nikon objective lens is used to
focus the trapping laser beam. The lens
focuses the beam to a 1.1um spot. The
power of the laser here is approximately
42% of the output power of the trapping
laser source. Following the sample, there
are only diffuse reflections of the beam.
g. Visible light from the LED light source
illuminates the sample and is then imaged
onto the CCD camera. The dichroic mirror in
the light path prevents backscattered light
from the 980nm laser from saturating the
CCD detector.
Note: Some extra details included that the TA can discuss while demonstrating the beam path.
G.4 – Post-Experiment Assessment
50
APPENDIX H – Safety Sheet
Optical Tweezers
Safety Guidelines
1. Place “Laser Work in Progress” sign on the door.
2. All unauthorized people must exit the room.
3. Ensure the room door is closed. If someone enters the room
unexpectedly, turn the laser off immediately.
4. Remove wristwatches or other reflective jewellery.
5. Remove any unnecessary items from the apparatus table.
6. Laser safety glasses must be worn at all times.
7. Contact the TA/Instructor if beam alignment is necessary.
8. In case of an emergency, contact UofT St.George Police: 416-978-2222.
9. If in doubt, TURN THE LASER OFF!
51
52
APPENDIX I – Laser Safety Quiz
I.1 – Laser Safety Quiz Questions
Laser Safety Quiz
1. What is the laser classification of the Optical Tweezers apparatus? Under what conditions is it
dangerous?
______________________________________________________________________________
2. What wavelength does the Optical Trap employ?
A) 550nm
B) 720nm
C) 980nm
D) 1400nm
3. What laser classification has the apparatus been re-classified to? Why?
______________________________________________________________________________
______________________________________________________________________________
4. Most laser related eye injuries occur during beam alignment:
T / F
5. For a laser emitting light at a wavelength between 400nm – 1400nm:
a) What part of the eye absorbs the beam?
__________________________
b) What is the amplification of the human eye?
A) 10X
B) 25X
53
C) 100X
D) 100,000X
c) List (3) associated eye hazards if laser safety glasses are not worn.
______________________________________________________________________________
______________________________________________________________________________
6. List the (4) safety precautions that must be carried out prior to turning on the laser.
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
7. Describe the procedure that must be followed if someone suddenly enters the room.
______________________________________________________________________________
______________________________________________________________________________
8. List the 2 aspects of laser safety glasses that must be checked before selecting an appropriate
pair.
______________________________________________
______________________________________________
9. During which portions of the experiment must the laser be turned off? Why?
______________________________________________________________________________
______________________________________________________________________________
54
I.2 – Laser Safety Quiz Solutions
Laser Safety Quiz
1. What is the laser classification of the Optical Tweezers apparatus? Under what conditions is it
dangerous?
Class 3B. When the eye is exposed to direct and specular reflections of the beam.
2. What wavelength does the Optical Trap employ?
A) 550nm
B) 720nm
C) 980nm
D) 1400nm
3. What laser classification has the apparatus been re-classified to? Why?
Class 1 Working Environment.
Safety interlocks have been included to enclosure the open-beam region.
4. Most laser related eye injuries occur during beam alignments:
T / F
5. For a laser emitting light at a wavelength between 400nm – 1400n:
a) What part of the eye absorbs the beam?
Retina
b) List (3) associated eye hazards if laser safety glasses are not worn.
Overheating
Retina burns
Scars/blind spots
55
Loss of central vision
Loss of peripheral vision
c) What is the optical gain of the human eye?
A) 10X
B) 25X
C) 100X
D) 100,000X
6. List the (4) safety precautions that must be carried out prior to turning on the laser.
- Place the Laser Work in Progress sign on the door
- Close and lock the door
- Remove wristwatches or reflective jewellery
- Wear laser safety glasses at all times
7. Describe the procedure that must be followed if someone suddenly enters the room.
Turn off the laser immediately
8. List the 2 aspects of laser safety glasses that must be checked before selecting an appropriate
pair.
Optical Density
Wavelength
9. During which portions of the experiment must the laser be turned off? Why?
While changing samples, because reflections of the laser may occur
56
APPENDIX J – Sample Data
Sample data can be found on the desktop in MP248 in the folder “Optical Tweezers” under the C:\ Drive.
This contains a video in .avi format that captures a trapped bead. A matlab file, positions.m, will convert
the .avi file into x and y positional data to facilitate data analysis and calculation of the trap stiffness.
A trapped bead should appear as in the following image:
Figure F1: Image of a trapped bead through the CCD camera.
APPENDIX K – Existing Optical Trapping Lab Manual
APPENDIX L – Modifications proposed by the client
It is expected that several students in the upcoming semester will focus on the Optical Tweezers,
according to Professor Bailey. As such, these students can further revise the student manual based on
the improvements and modifications proposed by our client:
 Begin with a more general introduction with reference to Boltzmann’s constant (as this is a
good way to test the Physics behind trapping) and refer to cell stiffness later in the
proceeding sections.
 Establish a clear approach to the safety protocol. The apparatus has been re-classified as a
Class 1 Working environment, though certain steps (such as wearing safety goggles) must
still be obeyed as if it were a Class 3 apparatus. However, safety instructions should be
delivered to the student as if it were a Class 3 apparatus to instill fear in the students and
avoid misconduct.
 The files required for the control of the Piezo Sample Stage could not be located by Jimmy
Shen or Professor Ryu on the desktop in his lab. Jimmy has agreed to look into this further,
as these files are necessary for nanometer movements through the Piezo controller.
The following is a list of resources that were consulted throughout the design process and their contact
information if further assistance is required:
57
Contact Person
Optical Trapping apparatus
manufacturer – ThorLabs
Contact Information
General:
techsupport@thorlabs.com
Esem Bweh-Esembeson
Ludwig Eichner, Senior R&D
Engineer:
leichner@thorlabs.com
Jimmy Shen
js2436@cornell.edu
Reason for contact
 Assistance with interlock
solution
 Laser diode interlock
details
 Trouble-shooting
interlock



Professor Will Ryu
wryu@physics.utoronto.ca


Created existing student
manual
Clarification on
procedures
Assistance with running
experiment
Faculty member in
charge of Optical
Tweezers experiment
Obtaining LabView files
58