Common Path Interferometer Using Optically Induced Molecular Reorientation In Liquid Crystals

Abstract

Optically induced molecular reorientation in nematic liquid crystals has been used to obtain a common path interferometer for measuring aberrations of the incident beam. When a strong laser beam is focussed onto homeotropically aligned liquid crystals, it produces above a threshold value, a molecular distortion, the profile of which depends upon the point spread function of the incident beam. The strong zero spatial frequency component creates a highly distorted centre due to the crystal birefringence producing a diverging spherical reference wavefront. This interferes with the directly transmitted aberrated wavefront producing fringes in the same way as in the point-diffraction interferometer. This interference phenomenon occurs in the extraordinary wave and resulting fringes represent directly the thickness contours of the incident wave.