Defocus Measurement Using A Liquid Crystal Point Diffraction Interferometer

A liquid crystal phase-stepped point diffraction interferometer (LCPDI) has been developed to measure optical wavefronts[1]. A locally generated reference beam is generated by diffraction from a microsphere embedded in a thin liquid crystal layer. Phase shifting is achieved by applying a voltage across the birefringent liquid crystals to shift the phase of the object beam without affecting the reference beam. The intended application for this instrument is the measurement of phase objects, such as optical elements and slowly varying fluids.