Beyond the lifetime of the Hubble Space Telescope, observational access to the ultraviolet (UV) might be quite limited. Therefore, small missions with short development times are required to bridge the gap to future larger missions in this important wavelength range. Even with the progress in adapting silicon sensors for the UV, single-photon-counting and visible-blind microchannel plate (MCP) detectors can provide a competitive signalto- noise performance, particularly in the far- and extreme-UV, and enable simple instrument designs for small and cheap missions.
Our MCP detector development aims at reaching enhanced sensitivity and increased lifetime with lower size, mass, and power consumption. Therefore, the design comprises (Al)GaN photocathodes with a tunable long-wavelength cut-off, long-life borosilicate MCPs, and a cross-strip anode with an FPGA-based readout.
In this contribution, we report on the overall status of the detector development and give an outlook on the mission prospects.
We present the status of our imaging and photon counting UV-MCP detector versions, sensitive in the ultraviolet wavelength range. The detectors have a spatial resolution of 2k pixels per axis, are photon counting, have no readout noise and a very low dark rate, making it ideal for photometry and spectroscopy. The detector can be easily adapted to the requirements of different missions, e.g., only the mechanical interfaces and an electrical interface must be defined to integrate the detector, it is relatively lightweight (3 kg) and has a power consumption of only 15 W. For the sealed version of the detector, we are currently testing a sealed detector head with a cesium telluride photocathode in semitransparent mode. The open version of the detector uses a lightweight door mechanism and is currently optimized to use a KBr photocathode. Interesting advances have been made for AlGaN on MgF2 and MgO substrates. A complete h-GaN film could be grown on MgO (0 0 1), and a complete c-GaN film on MgO (1 1 0). Good crystal quality is crucial to obtain a high QE AlGaN photocathode. Finally, the challenges towards a sealed detector head with a diameter of about 8 cm are described. By rotating the detector window on the detector head during the sealing process, we were able to seal the detector. The photocathode in the sealed MCP detector is stable for at least weeks.
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