Experiment 9: Polarization of Light
Objectives:
 Understand the concept of polarization.
 Apply Malus’s Law to predict intensity of light transmitted by a sequence of
linear polarizers.
 Understand how light can be polarized when reflected off a surface.
 Understand and apply Brewster’s Law.
Pre Lab:
You will be performing the polarization experiment described in Project #8 of the
Projects in Optics workbook. Read Project #8 Polarization and Section 0.5.1 of the
Primer. Answer the following questions:
1) Malus’s Law: In Figure 1, randomly polarized light passes through a linear polarizer
with transmission axis oriented at 0° with respect to vertical. The transmitted light
has intensity I(0). The polarized light passes through a second linear polarizer with
transmission axis at 30° with respect to vertical. Predict how much light from the
first polarizer is transmitted by the second polarizer, expressed as a fraction of I(0).
θ = 30°
θ = 0°
Random
I(0)
Figure 1
2. Brewster’s Angle:
a) Give the formula for Brewster’s angle. Define all terms.
b) Calculate Brewster’s angle for light traveling through air (n=1) and reflecting off
water (n=1.33).
c) Brewster’s angle is the angle at which all reflected light is polarized perpendicular
to the plane of incidence. Draw a diagram of this phenomenon. Include the
incident ray, reflected ray, transmitted ray, Brewster’s angle, surface plane, and
plane of incidence.
d) In part c), what happens to the parallel polarization component of the incident ray,
considering that it’s not reflected?
3. Use the introduction to Project #8 to answer the following questions:
a) What is mode sweeping, in your own words?
b) How might mode sweeping affect your intensity measurements?
c) What two steps are recommended to minimize the effects of mode sweeping?
The Lab
Perform Project #8 Polarization in the “Projects in Optics Workbook”, with the following
deviations:
1)
In step 4, an intensity detection method(s) will be provided in class.
2)
In steps 5 and 6:
a. Extra credit to anyone who can find the specified notch on the polarizers. (Do
not construct one).
b. In the absence of a notch, align the two polarizers to minimize transmission.
Call this angle 90°. Take intensity measurements every 10° for 180°. A table
is provided below for your convenience. For the “Theoretical Irradiance”
column, use Malus’s Law to calculate the intensity as a fraction of the
experimental maximum intensity (recorded at relative transmission axis angle
of 180°).
c. Repeat for a second series of data, if time permits, and merge results.
Rotation stage
angle (θRS)
Series 1
Series 2
Relative angle Irradiance
of transmission
axes, θ
Series 1 Series 2
90°
100°
110°
120°
130°
140°
150°
160°
170°
180°
190°
200°
210°
220°
230°
240°
250°
260°
270°
Theoretical
irradiance
Series 1 Series 2
0
0


Deliverables
Based on your experience with this lab, write a 2-4 page report discussing your technique
and your findings. Follow the format described in Lab Policies. Results should include
your data, equations, the plot described in Step 6 of Project #8, and a comparison of your
experimental Brewster’s angle for glass with the theoretical value given in Section 0.5.1.
Considerations
In addition to your results, discuss the following questions in a subsection of the
“Discussion” section entitled “Considerations”:
1) The data sheet states that lasers we used have random polarization, but we saw in
a previous lab that the laser has three modes, which are orthogonally polarized.
How do you reconcile these seemingly contradictory statements? Include the
concept of mode sweeping in your discussion.
2) Did you observe any phenomenon which may have been caused by mode
sweeping?
3) Polarization of light comes into play as a design consideration in several
engineering applications. Choose one such application and discuss how it makes
use of polarization. Suggestions include LCDs, Kerr cells, Pockels cells, fiber
optics, and optical communication encoding methods.