Phys 198 January 22, 1997
The presence of two indices, different for different E field directions, means that there will be a phase difference, or retardation, between the two components exiting from a birefringent plate. This retardation is determined by t|n1 -n2| where t is the thickness of the material.
If linearly polarized light is passed through a birefringent material with the polarization direction splitting the angle between the fast and slow axes of the material, the two components exiting from the material can be brought together again by using a second linear polarizer, called an analyzer. Since n for any material is wavelength dependent, there will be a different phase difference for each wavelength or color in the two beams. Since the components have the same frequency, are coherent, and have the same polarization they will interfere with each other. If the phase difference for any particular color in the beams is an odd multiple of a half a wavelength that color will undergo destructive interference and will be removed from the output. This is called color extinction.
Interference between light reflected from the top and bottom of a thin film. Newton's rings. Remember possible phase change upon reflection from an interface. ("High to low, phase change no; low to high, phase change pi.")
Birefringence by a calcite crystal which produces two output beams polarized orthogonal to each other. The beams are separated if the light beam enters at an angle to the third axis (the axis perpendicular to the two axes with different indicies of refraction), otherwise the beams remain coincident.
Color changes occur in the beam exiting from the birefringent material when the analyzer through which it is viewed is rotated. This is the color extinction effect.
Diffraction by a single slit, a square aperture, and a circular aperture (Airy disk).
Interference by two slits (Young's experiment), and by a grating; the interaction between interference and diffraction effects.
The data images taken in the lab and various questions of analysis are given in Diffraction Experiments.
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