a. Characteristics (Figure 1): depth, duty cycle, shape, frequency

b. Styles: Chopper, polarization, frequency modulation (grating dither), transient grating (nonlinear effect, crossed laser beams), Interference

2. Polarizers -- random in - linear out (E field with specific orientation)

-- IR: reflection: wire (grid) made like a grating (narrow spacing l > 2d), Al on ridges

-- use Brewster angle (stack of plates), each one loses some intensity from a specific polarization and transmits all of the other polarization

-- use birefringence index — total internal reflection (Glan Prism) one polarization is transmited with some reflection loss, the other totally reflected (narrow angle of acceptance), Glan Taylor has air gap, narrow angle of acceptance, capable of high power

-- beam split (Rochon, Wollaston etc.), transmit both, but divergent angle, if beam is collimated, can separate at a distance, MgF₂ used in vac-uv as Rochon, LiIO₄ sometimes as a Wollaston

-- birefringence retardation, d, depends on wavelength, l, the difference in refractive index, Dn = n_x-n_y and thickness, z, d = (2p/l) Dn z

-- as light passes through crystal, shift phase of two orthogonally polarized beams (x,y), when recombine, if l/4 shift (d = p/2) then circular (left or right), if d = p (or l/2) then perpendicular linear polarization results–other values give elliptically polarized light

-- Soliel-Babinet compensator will do this vaiably by sliding a wedge into the beam to vary z

b. Fresnel rhomb -- reflection retardation -- broad band circular polarization

-- Photoelastic — periodic stress induce birefringence — any isotropic material acoustically matched to driver can be basis, wide spectra region possible, periodic retardation, variable amplitude or wavelength of l/4 (right to left circular) or l/2 (parallel to perpendicular linear) retardation

d. Faraday rotator — magnetic field rotate linear (not circ.) polarization to new orientation