High Speed pn-CCDs as Wave Front Sensors in Adaptive Optics Systems

Abstract

Fully depleted silicon pn-CCDs with an active thickness of 300 μm exhibit a quantum efficiency of 90% at a wavelength of 1 μm in the near infrared. The multiparallel readout architecture allows for a frame time shorter than 2 ms for a device having a format of 256×256 pixels. It can be operated in a full frame mode and in a frame store mode. The pixel size is 50x50 μm. The active area is then 12.8×12.8 mm2. Cooled down to -90°C the electronic noise floor is below 4 electrons (rms). A camera system with comparable specifications — except for the pixel size — has alreadybeen fabricated for ESA’s XMM mission, which was launched on 10th December 1999. There are plans to develop a data acquisition system, which is able to handle the desired data rate of up to 50 Megapixel per second with a dynamic range of 12 bits. The detector is supposed to operate as a wavefront sensor in adaptive optics systems. The high speed, low noise and high quantum efficiency at longer wavelengths offers additional sensitivity for on-line wavefront corrections. Future work includes the extension of the active area to 1000×1000 pixels, monolithically fabricated on a high resistivity 6-inch silicon wafer. The main driver for this development is the planned XEUS mission, to be launched at the end of the next decade.KeywordsQuantum EfficiencyInternal Quantum EfficiencySignal ChargeEntrance WindowAdaptive Optic SystemThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.