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Physics 212 Lecture 24: Polarization

Physics 212 Lecture 24: Polarization. Main Point 1. First, we defined what we had previously called “plane harmonic waves” as linearly polarized waves. In particular, we defined the direction of polarization to be the axis of the electric field oscillations of the plane wave. Main Point 2.

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Physics 212 Lecture 24: Polarization

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  1. Physics 212 Lecture 24: Polarization

  2. Main Point 1 First, we defined what we had previously called “plane harmonic waves” as linearly polarized waves. In particular, we defined the direction of polarization to be the axis of the electric field oscillations of the plane wave.

  3. Main Point 2 Second, we introduced polarizers, materials that totally absorb the E-field component perpendicular to its transmission axis, while completely passing the E-field component parallel to that axis. Consequently, light passing through these polarizers is linearly polarized along the transmission axis. If the incident light is unpolarized, the transmitted light has half the initial intensity, while if the incident light is linearly polarized, the intensity of the transmitted light is equal to the incident intensity times the cos2q, where q is the angle between the initial polarization direction and the transmission axis.

  4. Main Point 3 Third, we introduced circular polarization in which the E-field oscillations in two orthogonal transverse directions were 90 degrees out of phase with each other. We distinguished between right-handed and left-handed circular polarization by observing the sense of rotation of the E-field oscillations in space at a fixed time. Circular polarization can be produced by passing linearly polarized light through birefrigent materials that have an asymmetric structure in transverse directions which results in the speed of light being different in each of those directions.

  5. Linear Polarization

  6. An unpolarized EM wave is incident on two orthogonal polarizers. Two Polarizers Checkpoint 1a What percentage of the intensity gets through both polarizers?A. 50% B. 25% C. 0%

  7. An unpolarized EM wave is incident on two orthogonal polarizers. Two Polarizers Checkpoint 1b Is it possible to increase this percentage by inserting another Polarizer between the original two?A. Yes B. No

  8. Identical linearly polarized light at 45o from the y-axis and propagating along the zaxis is incident on two different objects. In Case A the light intercepts a linear polarizerwith polarization along the y-axis In Case B, the light intercepts a quarter wave platewith vast axis along the y-axis. Checkpoint 2a A B Compare the intensities of the light waves after transmission.A. IA < IBB. IA = IB C. IA > IB

  9. Identical linearly polarized light at 45o from the y-axis and propagating along the zaxis is incident on two different objects. In Case A the light intercepts a linear polarizerwith polarization along the y-axis In Case B, the light intercepts a quarter wave platewith vast axis along the y-axis. Checkpoint 2b A B Checkpoint 2b A B What is the polarization of the light wave in Case B after it passes through thequarter wave plate?.A. linearly polarized B. left circularly polarizedC. right circularly polarized D. undefined

  10. Identical linearly polarized light at 45o from the y-axis and propagating along the zaxis is incident on two different objects. In Case A the light intercepts a linear polarizerwith polarization along the y-axis In Case B, the light intercepts a quarter wave platewith vast axis along the y-axis. Checkpoint 2c A B Checkpoint 2c A B If the thickness of the quarter-wave plate in Case B is doubled, what is the polarization of the wave after passing through the wave plate?A. linearly polarized B. circularly polarizedC. undefined

  11. At t=0 Example: There is no reason thatfhas to be the same for Exand Ey: Makingfxdifferent fromfycauses circular or elliptical polarization:

  12. Right hand rule Q: How do we change the relative phase between Ex and Ey? A: Birefringence By picking the right thickness we can changethe relative phase byexactly 90o. This changes linear to circular polarization and is called a quarter wave plate

  13. Circular Light on Linear Polarizer Q: What happens when circularlypolarized light is put through apolarizer along the y (or x) axis ? • I = 0 • I = ½ I0 • I = I0

  14. Polarizers & QW Plates: Circularly or Un-polarized Light Polarized Light Birefringence RCP Executive Summary:

  15. Calculation Light is incident on two linear polarizers and a quarter wave plate (QWP) as shown. What is the intensity I3 in terms of I1? fast 45o y x slow 60o I1 I2 z I3 • Conceptual Analysis • Strategic Analysis

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