Patent ID: 6738137
Filing Date: 2004-05-18
Classification: G01N

Abstract:
An apparatus for establishing retardation induced by a waveplate that exhibits birefringence, comprising:a source of polarized light arranged such that the light propagates along a path from the source; a light detector located in the path substantially opposite the source; a photoelastic modulator having an oscillating part located in the path between the source and detector such that the light propagates through the oscillating part of the photoelastic modulator; a waveplate rotatably mounted in the path so that the light propagating through the oscillating part of the photoelastic modulator propagates through the waveplate to be incident on the light detector, wherein the retardation of the waveplate correlates to the intensity of the light that is incident on the detector, and whereby the detector produces an output signal indicative of the intensity; and means for mounting the waveplate in the optical path for selectively tilting the waveplate thereby to vary the value of the established waveplate.