Parameters
lam : wavelength of the propagating wave
ni : refraction index of the medium before the plate
n_o : ordinary refraction index of the birefringent material
n_e : extraordinary refraction index of the birefringent material for a plane wave propagating perpendicularly to the optical axis
teta : angle of the incidence plane referred to an axis parallel to the facets
i : angle of incidence
thi : plate thickness
ro : refraction angle for the ordinary wave
re : refraction angle for the extraordinary wave (the direction of the extraordinary wave corresponds here to the direction of the phase velocity / wave vector)
m : order of the birefringent plate
