Sub-Nyquist interferometry using a computer-stored reference

Abstract

In the testing of deep aspheric wavefronts using the phase-shifting technique a CCD video camera and a digital computer is limited by the so-called Nyquist frequency. The Nyquist frequency limits the maximum wavefront slope that can be measured over the CCD array to π radians per pixel. A wavefront containing spatial frequencies beyond this limit gives a sub-sampled or aliased interferogram. If the wavefront under test is assumed to be smooth up to its first or second derivative, then it is possible to recover the deep aspheric wavefront. Here we present a new and simple technique to recover a deep aspheric wavefront under test whenever a close estimation of the wavefront being tested is available.