1. Topics
Use birefringence to generate and quantify elliptically polarized light.
Understand, measure and characterize the optical activity of syrup.

2. Birefringence
Fast axis: n2
Slow axis : n1
The birefringent retarder in your box causes a phase delay of 140nm (approximately 0.22*llaser). Phase delay depends on the thickness of the birefringent material.

3. Retardation in a ”l/4-waveplate” for light polarized linearly at 45 with respect to main axes (=superposition of two orthogonal in-phase linearly polarized waves)
Fast axis y
Slow axis x F E C B A D x y x y x y A B C
Has fallen behind by l/4
Polarization before the l/4-waveplate: When looking against the direction of light propagation: A, B, C, … pass you by successively. D x y x y x y E F

4. Polarization after the ”l/4-waveplate”
Fast axis y
Slow axis C D x F A E B x y x y x y D x y x y x y E F A B C
This light is “left-circularly” polarized (What does electric field do at one point in space when looking against propagation direction – Physics definition; careful: EE is opposite!).

5. V.D Measure transmitted intensity I as a function of Retarder orientation Q
Polarizer
Retarder
To photometer
Laser
Vary the orientation Q of retarder.
Measure I(Q) and plot I versus Q .
Discuss the result in terms of the retardation properties of the retarder.

6. V.D Measure intensity I as a function of polarizer orientation Q
Polarizer/Analyzer
Retarder at 45 angle to laser polarization.
To photometer
Laser
Set retarder so that either the slow or the fast axis is at a 45 angle with respect to the laser polarization.
Vary the orientation Q of polarizer(used as an analyzer).
Measure I(Q) and plot I versus Q on polar graph paper.
Write down exactly how the retarder was oriented with respect to the laser polarization and figure out whether the light got left- or right-polarized in your setup.

7. n n Optical Activity Left circularly polarized light
Right circularly polarized light n

8. Linearly Polarized Light = Superposition of Circularly Polarized Light (left and right)+ =

9. …and if one circular polarization is phase shifted…+ =

10. Rotation Due to Optical Activityb
n and n d
Linearly polarized light
Linearly polarized light – different orientation Polarization rotated by angle b

11. Dextrorotary versus Levorotary
(“Looking” against the direction of light propagation.)
Dextrorotary
Levorotary b b
before
after
after
before
Optical activity causes a rotation of polarization to the right.
Optical activity causes a rotation of polarization to the left.