A CCD Based Curvature Wavefront Sensor for Adaptive Optics in Astronomy

Download or read book A CCD Based Curvature Wavefront Sensor for Adaptive Optics in Astronomy written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Adaptive Optics (AO) is a technique for compensating the distortions introduced by atmospheric turbulence in astronomical imaging. To measure the distortions a wavefront sensor is needed. There are a number of fundamentally different types of wavefront sensors, one of which is the curvature wavefront sensor. At the European Southern Observatory (ESO) in Garching, Germany, several adaptive optics systems using curvature wavefront sensors are being developed for the Very Large Telescope (VLT) and the VLT interferometer (VLTI). Curvature AO-systems have traditionally used avalanche photodiodes (APDs) as detectors due to strict requirements of very short integration times (200 microsec) and very low readout noise. Advances in charge-coupled device (CCD) technology motivated an investigation of the use of a specially designed CCD as the wavefront sensor detector in a 60-element curvature AO system. A CCD has never been used before as the wavefront sensor in a low light level curvature adaptive optics system. This thesis shows that a CCD can achieve nearly the same performance as APDs at a fraction of the cost and with reduced complexity for high order wavefront correction. Moreover the CCD has higher quantum efficiency and a greater dynamic range than APDs. A readout noise of less than 1.5 electrons at 4000 frames per second was achieved. A back-illuminated thinned version of this CCD can replace APDs as the best detector for high order curvature wavefront sensing. This thesis presents the concept, the design and the evaluation of the CCD. The first frontside devices were successfully evaluated and the performance of the detector was proven in a laboratory experiment.