The optomechanical and electronic design of the SPADA wavefront sensor is driven by the requirement to be compatible with the ESO MACAO systems, replacing the lenslet-fibre-APD module section of the wavefront sensor. SPADA is also designed to be applied to the CALDO pulse laser LGS-AO experiments, foreseen by ESO in collaboration with the Durham University. Moreover on board processing has been added to use the SPADA in standalone mode as curvature sensor analyzer and as a Fast Transient (FT) phenomena detector. The readout is in parallel for all pixels and takes few tens of nanoseconds per photon; hence, the upper limit of the dynamic range can attain several million of counts per second.
The whole system consists of a "Detection Board" for detecting the ignition of each element and a "Data Processing Board" based on FPGA and DSP able to acquire all the pixel signals and perform the photon-counting and real-time processing. A remote computer with appropriate software procedures is used to provide the system control, data uploading and postprocessing. The block diagram of the entire SPADA system is shown in Figure 6.
At the moment the lenslets array (already available at ESO for the MACAO instrument), the SPADA chip, the detection board, the data processing board and the data acquisition software are completed and some operational tests have been carried out in laboratory. Only the mechanical housing is under construction and we expect to assemble the entire system at the end of this year.
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