NEW TECHNIQUE FOR RAY ABERRATION DETECTION IN HARTMANNGRAMS BASED ON REGULARIZED BANDPASS-FILTERS

The Hartmann test is a well-known technique for testing large telescop es mirrors. The Hartmann technique samples the wavefront under analysi s using a screen of a uniformly spaced array of holes located at the p upil's plane. The traditional technique used to gather quantitative da ta requires the measurement of the centroid of these holes as imaged n ear the paraxial focus. The deviation from its unaberrated uniform pos ition is proportional to the slope of the wavefront's asphericity. The centroid estimation is normally done manually with the aid of a micro scope or a densitometer. Traditional techniques for carrier frequency fringe analysis cannot be used to analyze Hartmanngrams because this p attern contains many spatial frequencies hard to eliminate using stand ard linear filters. Also due to the finite extent of the pupils, Fouri er transform methods and convolution filters with large support are no t well suited for the analysis. We propose a new technique based on re gularized bandpass filters to detect the transverse aberration in Hart manngrams. These filters are used to transform the distorted 2-D dot p attern of the Hartmanngram into two orthogonal linear-carrier phase-mo dulated cosinusoidal gratings. The resulting cosinusoidal fringe patte rns are then well suited for the analysis using highly sensitive 2-D c arrier frequency phase estimation techniques such as direct interferom etry. (C) 1996 Society of Photo-Optical Instrumentation Engineers.