High-Resolution UV Detectors for Large Focal Plane Instruments

Potential future NASA satellite missions in the ultraviolet (e.g., LUVOIR (LUMOS) and HabEx (UVS) have baselined MCP detectors) will require very large format (up to 400 cm2), high-resolution detectors for both imaging and spectroscopy. The objective of this program is to move the current state of the art in UV detectors closer to fulfilling these requirements. We propose to exploit several emergent technologies including microchannel plates functionalized by atomic layer deposition, large area refractory cross strip anodes compatible with current readout electronics developments, large format square vacuum tube sealing, and high efficiency/low noise photocathodes. The end goal is to develop these technologies to enable a practical solution for a high spatial resolution, 100 x 100 mm2 detector in a hermetic sealed tube package. Atomic layer deposition (ALD) techniques and novel glass materials provide a new generation of enhanced performance microchannel plates (MCPs) being produced in very large formats (up to 400 cm2 with 20 µm pores and 160 cm2 with 10 µm pores). Using the basic technique of functionalizing (resistive and emissive layers) borosilicate micro-capillary arrays with ALD has resulted in significant achievements. These include producing large 20µm pore MCP formats with background rates of ~0.04 events/cm2/sec, and stable extended lifetimes ≥ 7 C/cm2 that are compatible with high temperature sealed tube integration. There has been recent success in the production of low resolution, very large square sealed tubes (200 x 200 mm2), albeit with significant dead area allotted to internal vacuum support structure. Non-refractory cross strip anodes have been produced in 100 x 100 mm2 formats and achieve >5 MHz single photon counting rates with position resolution <20 µm and timing resolution <100 ps. A current SAT synergistic project is also funded to develop a low power/mass ASIC to read them out and improve overall performance. Photocathodes (alkali halides, bialkali, GaN) have been used to establish high UV detection efficiency for MCP detectors and investigations to optimize the QE of these as solar blind photocathode materials is ongoing. Specific issues to be addressed in this investigation include an analysis of the design, materials, and techniques needed for a large area, high-resolution sealed tube as a hermetic refractory “system” that contains all of the necessary elements. The recent success with very large square ceramic based tube seals is promising. However incorporation of a high-resolution anode and establishment of the internal support structures presents their own set of structural and functional challenges to be overcome. The designs will need to be modeled for thermal and mechanical robustness and large area trial tubes need to be produced. Issues that need to be addressed include topics such as migration of the large format cross strip anode design to ceramic materials compatible with sealed tube manufacturing and that give the prerequisite imaging performance characteristics. In addition large MgF2 windows in >100 x 100 mm2 format, the window sealing process, dead area minimization between detector “panels”, vacuum enclosure materials and processes, electrical integration of MCPs and anodes in large format configurations all play a part in the successful realization of detectors for the decadal study mission concepts.

The Astrophysics Research and Analysis program (APRA) supports suborbital and suborbital-class investigations, development of detectors and supporting technology, laboratory astrophysics, and limited ground based observing. Basic research proposals in these areas are solicited for investigations that are relevant to NASA's programs in astronomy and astrophysics, including the entire range of photons, gravitational waves, and particle astrophysics. The emphasis of this solicitation is on technologies and investigations that advance NASA astrophysics missions and goals.

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