A half-wave plate ( ) has its fast axis at below the horizontal
PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Polarisation and anisotropic media · Polarisation and anisotropic media
Optics and Photonics, Ch Birefringence and crystal optics
Problem
A half-wave plate (Γ=π) has its fast axis at 20∘ below the horizontal, i.e. at −20∘. Horizontal linearly polarised light falls on it at normal incidence, at the plate's design wavelength.
((a)) Predict, before multiplying any matrices, the angle at which the light leaves the plate, then confirm the prediction with the Jones product R(θ)diag(1,eiπ)R(−θ) with θ=−20∘ acting on (1,0).
((b)) A circular photoelastic disc, loaded in diametral compression, is viewed between crossed polarisers in monochromatic light. Along the loaded diameter the retardance rises smoothly from zero at the centre of the disc to a value corresponding to 4.5 complete waves at the two points of contact with the loading jaws. State how many dark (isochromatic) bands are seen along this diameter, counting the one at the centre. If the experiment were repeated in white light, describe what replaces each dark band, and name (without applying) the tool from an earlier chapter that would be needed to compute the colours.