When a birefringent slab is rotated between two crossed polarizers, the four maxima and four minima of the transmitted intensity occur, as known, at every π/4 radians. If the slab is also optically active, the maxima and minima are arranged in other patterns that may be grouped according to the number of extrema met in one complete turn of the slab: four or eight. All the possible patterns are classified and each is related to some peculiarity of the complex refractive index of the slab.
© 1980 Optical Society of America
M. S. Giammarinaro and S. Micciancio, "Absorbing anisotropic and gyrotropic slab between crossed polarizers in parallel light," J. Opt. Soc. Am. 70, 429-432 (1980)