Question

Light passes through a system of two crossed Nicol prisms between which a quartz plate cut at right angles to its optical axis is placed. Determine the minimum thickness of the plate which allows light of wavelength 436 nm to be completely cut *** by the system and transmits half the light of wavelength 497 nm. The specific rotation constant of quartz for these wavelengths is equal to 41.5 and 31.1 angular degrees per mm respectively.

Answer 1

For light of wavelength 436 nm

(Light will be completely cut when the quartz plate rotates the plane of polarization by a multiple of 180°.) Here d = thickness of quartz plate in mm. For natural incident light, half the light will be transmitted when the quartz rotates light by an odd multiple of 90°. Thus*