Development of a novel photon counting detector for UV spectrographs

Spectroscopic observations in the far and extreme ultraviolet (FUV/EUV, 40-200nm) is of great interest in various scientific fields, such as in Solar Physics, in physics of interstellar medium and in planetary exospheres studies. Microchannel plates-based detectors have been for a long time the detectors of choice for astronomical applications in this range of wavelength, due to their photon counting capability (since the expected photon flux are low) and the possibility of solar blindness (photon flux in the visible range are order of magnitudes higher and filtering may be an issue). However, the spectral features observed in the targets are characterized by a high range of intensities, which can cover several orders of magnitude. Response of MCP detectors at high flux is limited ultimately by the MCP itself, but generally the readout system introduces further restrictions, thus the technique of lowering the efficiency in the area interested by the most intense lines is often adopted. In the framework of technological R&D for future astronomical FUV/EUV spectrograph, we are developing a photon counting, solar blind, UV detector with readout system based on a 2D anode array integrated in a custom designed Read Out Integrated Circuit (MIRA - Microchannel plate Readout ASIC), with the aim of achieving high performances characteristics, in particular unprecedented performance in terms of dynamic range combined with spatial resolution close to 30 mu m. This detector will allow to measure, simultaneously and without the necessity of filters, spectral lines with different intensities of orders of magnitude, exploiting the maximum Signal to Noise Ratio provided by the statistical limit. A first prototype has been realized, based on a demonstrator of the MIRA ASIC, 32x32 pixels, 35x35 mu m(2) size, for a total chip area of 2x2 mm(2), to be integrated with a standard demountable MCP intensifier.