Fresnel Image Wavefront Sensor With High Sensitivity and Variable Spatial Sampling

To reduce the complexity of Hartmann sensor optics and to adapt the wavefront sensor (WFS) to variable spatial sampling, Physical Optics Corp. proposes to design a novel WFS based on the Fresnal Image (FI) effect whereby a periodic structure illuminated by coherent light will image itself with variable multiplication depending upon the position of the observation plane. Local wavefront distortion (deviation from a plane or a sperical wavefront) causes displacement of corresponding elementary images sonstituting an FI of a periodic structure. A simple algorithm is proposed to compute wavefront local tilt from displacement measurement. The WFS has various advantages over other methods. The optical system is extremely simple, can be implemented in any spectral range, and give a clear two-dimensional pattern of inhomogeneties of the aerodynamic field. By selecting the transmittance profile of the elementary object, it is possible to adjust the WFS spatial sampling rate to the medium under investigation. The method can be used for long-aperature analysis and has higher sensitivity than the Hartmann method. A high rate of temporal sampling will be achieved by employing two 15KHz frame rate dedicated CCD arrays and POC's proporietary 48 DSP boards permitting highly parallel image processing.