Phase difference controller and method for controlling phase difference

Abstract

Phas difference controller for use in equipments having a photoelastic modulator, such as ellipsometers and optical rotatory dispersion meters. For enabling the photoelastic modulator to produce the constant amplitude of the phase difference regardless of the change in the wavelength of light incident into the photoelastic modulator, and regardless of the change in the temperature of the photoelastic modulator itself or its atmosphere, the controller has a birefringence polarizer which splits incident light into two linearly polarized light beams, ordinary light and extraordinary light. One of them acts as reference light LR and the other one acts as main light LM. These light beams pass through a photoelastic modulator which is forced to vibrate at angular frequency of .omega.. After that, the passed reference light LR is detected by a photomultiplier via an analyzer. The photoelastic modulator is forced to vibrate at angular frequency of .omega. so that the ratio of the amplitude of the ac component of angular frequency of 2.omega. to the dc component included in the output signal of the photomultiplier is maintained constant.