Overview 1. Introduction 2. Linear Polarizers Up Next:

1. Devices for Control of Polarized LightPART1- Practical info for the major classes of optical devices Fig A Glan-Taylor Polarizer Overview 1. Introduction 2. Linear Polarizers Up Next: 3. Retarders (e.g. electrically/magnetically variable retarders) 4. Depolarizers Mar. 14, 2006 http://www.che.ccu.edu.tw/~rheology/polarized/outline2.htm

2. 1. Introduction • Factors That Cause the Devices to Deviate from the Ideal: • Absorption of light & Dispersion (change of refractive index with wavelength ) • Geometrical considerations • Angular aperture (limited angular acceptance) Click Here • Spatial aperture (limited beam cross section) • Power handling & Efficiency • Expense • Special peculiarities - Some devices are excessively temperature dependent

3. 2. Linear Polarizers • General Characteristics • REVIEW OF BASIC OPTICSClick Here • Malus’s law Note: No real pair of polarizers can totally extinguish an incident beam when crossed (i.e., θ= 0) • Extinction ratio

4. How to measured intensities which differ by several orders of magnitude? ‧ ‧ ‧ ‧ Using a sensitive detector Crossed  Parallel

5. Birefringence Polarizers • In uniaxial crystals, two refractive indices are observed • no is observed for rays polarized perpendicular to the optic axis ordinary rays • ne is observed for rays polarized parallel to the optic axis extraordinary rays O.A. O.A.

6. The First Type - Producing two beams at a small angle to one another, each of which contains one polarization Normal vector Fig Wollaston prism for negatively birefringent (no>ne) material Fig Rochon prism for negatively birefringent (no>ne) material

7. REVIEW OF BASIC OPTICSClick Here (全反射) • The Second Type –Over a small range of angles, one polarization undergoes total internal reflection while the other is transmitted Fig Glan-Taylor polarizer for negatively birefringent (no>ne) material cement Fig Glan-Thompson polarizer for negatively birefringent (no>ne) material

8. Miscellaneous (各式各樣的) Polarizers • Stacked-Plates Polarizer: Plates all tilted at Brewster’s angle • Thin-Film Polarizer: A single plate with a multilayer dielectric coating - Reflected beam: > 99% polarized Transmitted beam: 95% polarized Polarized in the plane of the slide Unpolarized light Polarized out of the plane of the slide

9. Review of Basic Optics http://www.che.ccu.edu.tw/~rheology/basic_optics/outline.htm (see Chapter 8)

10. 2. Polarizers • Polarizer • Input: Natural light  output: Polarized light • Based on one of four fundamental physical mechanisms: a. Dichroism b. Birefringence c. Scattering d. Reflection • It selects a particular polarization state and discards all others (anisotropy in the material of the polarizer) FIG.A linear polarizer and analyzer

11. Malus’s Law Transmission axis Back FIG. A linear polarizer and analyzer

12. Review of Basic Optics http://www.che.ccu.edu.tw/~rheology/basic_optics/outline.htm (see Chapter 8)

13. : dipole • Polarization by Scattering • The dipole does not radiate in the direction of its axis • Increasingly more polarized as the angle increases FIG. Scattering of unpolarized light by a molecule FIG. Scattering of polarized light by a molecule

14. 3. Polarization by Reflection • A Wave Reflecting and Refracting at a Interface Transmission axis is parallel to the ground polarizer perpendicular

15. electron– oscillator

16. Contd. 30o 0o 60o 30o 60o The dipole radiation pattern

17. The reflected beam is strong in P-state light perpendicular to the plane-of-incidence and weak in P-state light parallel to the plane-of-incidence FIG. The pile-of-plates polarizer This plane FIG. The beamsplitter cube Back

18. Performance of Glan-Taylor prism for rays inside or outside the acceptance angle Incident beam Back

19. Fig A Glan-Taylor Polarizer Fig A Fresnel rhomb (retarder) Devices for Control of Polarized LightPART 2- Practical info for the major classes of optical devices Overview 3. Retarders 4. Depolarizers Mar. 28, 2006

20. 3. Retarders O.A. (快軸) • Birefringent Materials Isotropic material O.A. e-ray Birefringent material o-ray Anisotropic material (uniaxial) Fig. A half-wave plate showing how a net phase shift accumulates with the retarder

21. Birefringent Plate Retarders • Linear retarder - introducing a phase difference between two linear polarizations of light • Slow axis ( Fast axis 快軸) - the orientation of the polarization whose phase changes the most within the retarder • a O.A. Fast axis Click here e-ray Slow axis o-ray Anisotropic material (uniaxial)

22. How a zero-order retarder is made? • Adjustable (multiple order) devices may provide more flexibility ‧ ‧ e-ray o-ray ‧ ‧ ‧ ‧ o-ray e-ray ‧ ‧ Incident light adjustable

23. y x Quiz: Have you notice that this schematic diagram is plotted incorrectly?

24. Reflection Retarders • The Fresnel Rhomb linearly polarized Elliptically polarized Circularly polarized Fig. Operation of various reflection retarders

25. Variable retarders can be divided into two categories • . • Type 1: Mechanically variable retarders • Allowing any particular retardation • Slow time response (1) Soleil-Babinet compensator (2) Photoelastic modulator (PEM) Incident light

26. Type 2: Electrically Variable Retarders • Applied field • Orient molecules with dipole moments • Optically anisotropic •  Macroscopic anisotropy in n Fig. A Kerr cell ‧Response time is only limited by the rotational time constant of the molecules (ps) ‧Polar liquid: Nitrobenzene (硝基苯) ‧W/o alignment difficulties ‧Larger beam cross section Fig. A Pockels cell

27. 4. Depolarizers (偽的) • The depolarizer converts the polarized input into a pseudo-randomly polarized output Fig. A depolarizer

29. 石英 方解石 Back