Operating the Nd:YAG and Laser Interferometer System
The Nd:YAG and laser interferometer system in lab 310 in the Earth and Engineering Science
Building is a powerful tool in Non-destructive Evaluation (NDE). This system is capable of making
qualitative and quantitative measurements of a variety of samples and producing valuable data in
materials characterization. However, in order to operate this system, careful attention must be paid to
personal safety and maintaining the delicate optics of the system by following this instruction set and
practicing safe and intelligent operation of the system.
The following information will detail the technical information of both of the lasers in the
system, a brief summary of their operation, how to properly start the system, how to operate the
system correctly, how to shut the system down and includes throughout tips that will help to develop
confidence and proficiency in using this laser system. It is highly recommended that users of this laser
system read both laser manuals as they contain the complete information on operating and maintaining
these lasers. Further information can be found on both company websites and many resources on the
internet listed at the end of this document.
Important!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
When operating the laser system, ultimately, only
two things are paramount. Most importantly,
ALWAYS wear eye protection and ALWAYS exercise
caution and safety. Secondly, NEVER allow the laser
beam of the Nd:YAG to enter into the interferometer
aperture. This will result in irreparable damage to
the optics within the interferometer which will
expend valuable time and money.
Technical Information
Continuum Surelite Laser
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Pulsed laser with Nd:YAG crystal
Maximum Power : 4.5 watts
Pulse duration varies from 120 microseconds to 180 microseconds at a frequency of 1 to
10 Hz
Extremely dangerous to the human eye (if the beam directly enters your eye you will go
blind)
Model Number : SLI-10
Polytec Doppler Vibrometer
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Continuous Wave Helium Neon (HeNe) laser
Maximum Power : 75 milliwatts
Relatively safe (will not cause permanent blindness)
Model Number : Controller OFV-5000; Sensor Head OFV-505
Summary of Operation
The Nd:YAG and HeNe Doppler Vibrometer work in conjunction with one another to both
generate and detect ultrasonic waves. The Nd:YAG is a high powered/short pulsed laser that will
generate an ultrasonic wave when directed onto a sample using the energy conversion of
electromagnetic energy to physical displacement in the sample. This physical displacement can then be
measured by the vibrometer using changes in frequency or phase of its probe beam that is directed onto
the sample. The configuration for these measurements can be seen below in figure 1. By monitoring
both of the laser’s parameters we can make measurements and evaluations of samples and
nondestructively assess materials.
Figure 1
Start-up Procedure
Nd:YAG Laser
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Ensure the Laser power supply (pictured in
figure 2) is plugged in and properly grounded
Make sure the manual shutter at the aperture of
the laser cavity is closed and that the beam path
is clear of obstructions and has the proper optics
positioned to direct the beam to your sample
Flip the AC power switch located at the top right
of the power supply (noted in figure 2) to the on
position
Acquire the Nd:YAG key and use it to turn the
second on switch located next to the AC switch
and also noted in figure 2
As the Nd:YAG powers on it will run its
diagnostics check and will return an error
message on the LED screen if a check has failed.
Refer to the owner’s manual in the event of an
error message
Figure 2
If no errors are output, press the start/stop
button noted in figure 2 to turn the Nd:YAG’s
flashlamp on
Allow the flashlamp to charge the laser cavity for twenty minutes before opening the
internal shutter (the power supply will not allow the opening of the shutter before this
time period)
HeNe Laser
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Ensure the vibrometer is properly connected to its controller and the controller is
plugged in
Make sure the protective cap is placed on the aperture of the laser
Acquire the controller key and turn to the on position
Allow the laser to warm up for at least twenty minutes also to ensure accurate
measurements
Operation
The operation of the HeNe laser is very straightforward and simple. Our setup only requires you
to connect a BNC cable to the Auxiliary output on the face of the decoder. The other end of the BNC
cable is to be connected to an oscilloscope or a computer in order to receive the data.
The output of the decoder is a voltage ranging
Note: When taking data from the
from -1.5 volts to +1.5 volts. This output corresponds to a
vibrometer’s output cable,
physical displacement of 75 nanometers/volt. Meaning if
remember that the resistance of
the output of the laser to an oscilloscope is -0.5 volts, the
the device is 50Ω. If this setting
physical displacement at that moment was -37.5
is not chosen on your computer
nanometers. This data can now be observed qualitatively
or
or oscilloscope your data may be
analyzed qualitatively further with software such as
erroneous.
MATLAB.
The operation of the Nd:YAG is a little more complicated. In the scope of this instruction set,
only operation using the 1 to 10 Hz settings will be discussed but it is important to note that the Nd:YAG
laser can be programmed externally or used with a “single shot” method; this information is detailed in
the user manual.
After the Nd:YAG has warmed up, the external shutter may be opened under the condition that
all present have the proper eye protection and the Nd:YAG beam is directed to the sample or a beam
dump. After the external shutter is opened, the correct inputs must be entered from the face of the
laser power supply again pictured in Figure 3 and this process is numbered below.
1. Press the “select switch” depicted in figure 3 until
the LED display reads “P00”
 This setting is the frequency with
which the laser will fire and its inputs
include P00 to P10
2. Select the desired setting for your experiment
using the toggle switches to the left of the select
switch where P01 is 10 Hz or 10 pulses per second
and P10 is 1 Hz or 1 pulse per second (P00 is 0
pulses per second)
3. After setting the pulse division press the select
switch again until the “Voltage” LED to the right
of the LED display lights up
4. Ensure that this value is 1.34 Volts as this is a
proper voltage with which to operate the laser
5. Press the select switch again until the Q-SW
DELAY LED to the right of the LED display lights up
6. This value can be changed using the toggle
switches to affect the power output of your laser.
Figure 3
Values of 130 to 180 are very high powered values that only should be used when the
ultrasound generated is weak. Values between 120 and 130 are ideal to make nondestructive measurements. Values out of these ranges are not recommended (see manual
for details)
After these settings have been properly entered, you may press the internal shutter button
located to the right of the start/stop switch to open the shutter and begin lasing. When you have
completed your experiment press the internal shutter button again to terminate the lasing output.
Shutdown Procedure
Nd:YAG Laser
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Close the external and internal shutters
Turn the key to the off position
Flip the AC power switch to the off position
HeNe Laser
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Turn the switch on the back of the vibrometer to the off position
Place protective cap back onto the aperture of the vibrometer
Turn the key on the vibrometer controller to the off position
Conclusion
Now that you have read this manual, you are ready to safely and successfully operate this laser
system. Remember to always use caution, treat this system with respect and refer to the manuals for
additional information. Good luck with your experiments!
Additional Information
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The manuals for the lasers may be found in lab 310 but there is an online version of the
Continuum laser here: http://www.doylegroup.harvard.edu/wiki/images/a/a0/9960207_Rev_Q_Surelite_Manual.pdf
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The Continuum website is: http://www.continuumlasers.com/
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The Polytec website is: http://www.polytec.com/us/
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These links detail laser ultrasonics and may be helpful:
http://en.wikipedia.org/wiki/Laser_ultrasonics
http://www.cqe.northwestern.edu/sk/SK-Papers/B5_lutchapter_2003.pdf
http://www.tecnar.com/index.php/products/laser-ut