Semi-derivative real filter for the measurement of the wavefront distortion

Abstract

The paper deals with a computer simulation and an experimental realization of a new kind of an optical setup for simple and fast control of the wavefront distortion. The method is based on a 4f coherent light correlator setup with a semiderivative real filter placed in the Fourier plane. In the setup described the distorted wavefront passes through the filter located in the frequency plane of the correlator. In the output plane a camera registers the intensity of light whose gradient carries information about the shape of the wavefront distortion. The output image is simple to analyze and interpret because the intensity is directly proportional to the first derivative of the distortion of the input wavefront. The role of the computer simulations presented in the paper was, first of all, to check how the semiderivative real filter deals with various kinds and levels of distortions. Secondly, it was to estimate how the technical limitations of the filter and the setup can influence the quality of the results obtained. The experiment checked the possibility of using the setup for examining the distortion of wavefront caused by hot air. The experimental results obtained show that the method is suitable and effective for real-time monitoring of the distortion of the wavefront, which allows for its use in adaptive optics and phase visualization. The method also allows for measuring other phase objects where the gradient of the phase and the thickness of the object undergo abrupt changes.