Wavefront sensor employing a modulation reticle

Abstract

An incremental slope wavefront sensor having an optical system which focuses an incident wavefront to a focal point. A novel modulation reticle is positioned at the focal point, and is driven in linear oscillation along a single axis. The modulation reticle has a modulation pattern formed thereon by alternating triangular light transmissive areas and inverted triangular light reflective areas. A first detector array detects the wavefront which has passed through the transmissive areas and diverged from the focal point in a two dimensional array of zones. A second detector array detects the wavefront which has been reflected by the reflective areas and diverged from the focal point in a two dimensional array of zones. The output signals from the first and second detector arrays for each corresponding zone are differentially combined to form a differential output signal for each zone. The y position of detected radiation in each zone of the wavefront is obtained by multiplying its differential output signal by a weighting function proportional to the instantaneous velocity of the reticle. The x position of detected radiation in each zone is obtained by multiplying its differential output signal by a weighting function proportional to the instantaneous velocity of the reticle and by a square wave function having respectively positive and negative values when the displacement of the reticle along the single axis is respectively positive and negative with respect to a coordinate system defined by the modulation pattern.