Cross Strip Photon Counting Sensors - Pathway to Very Large Detectors for Ultraviolet Astronomy
This blog post originated in the 2018 Science Mission Directorate Science and Technology Report.
High Performance Sealed Tube Cross Strip Photon Counting Sensors
These sensors represent an important enabling step in the development of large-area, high-resolution, very sensitive ultraviolet sensors for future-generation large space telescopes currently under study, such as LUVOIR and HabEx.
Future-generation large space telescopes under study at NASA will require very large, high-resolution, high-sensitivity, low-noise sensors capable of measuring ultraviolet through visible wavelengths. Armed with these advanced detectors, these missions would be capable of detecting and characterizing potentially habitable exoplanets. The Experimental Astrophysics Group at University of California Berkeley, in partnership with Photonis USA and INCOM Inc., is developing the pathway technology to realize these large area sensors.
Large area microchannel plate (MCP) detectors are part of the baseline plan for ultraviolet (UV) spectrographs on two of the large mission concepts being studied for inclusion in the National Academy of Sciences Astronomy and Astrophysics Decadal Survey (Astro2020). The Large Ultraviolet/Optical/Infrared Surveyor (LUVOIR) Ultraviolet Multi-Object Spectrograph (LUMOS) and the Habitable Exoplanet Observatory Ultraviolet Spectrograph (HabEx-UVS) will provide improvements in high contrast imaging and sensitivity, spectroscopy, astrometry, angular resolution and wavelength coverage. Both missions propose to employ arrays of large (100 mm and larger) high-performance MCP detectors.
With SAT funding, the Experimental Astrophysics Group at UC Berkeley is advancing the state of the art in MCP detector technology to meet the requirements of potential future large space missions and a variety of small (Explorer) and medium size (e.g., Cosmic Evolution Through UV Spectroscopy, or CETUS) missions. These on-orbit UV facilities would be able to probe the very limits of the universe. Principal Investigator (PI) Dr. Oswald Siegmund notes that, “The development of these large area MCP detectors in the UV-Vis is an important enabling technology for the success of future missions like LUVOIR-LUMOS and HabEx-UVS.”
MCP detectors with cross strip (XS) readouts have demonstrated potential to combine high spatial resolution (<20 μm) with photon-counting (noiseless) imaging in a robust, radiation-hard package that is scalable up to very large formats (>10 cm with 5,000 x 5,000 resolution elements). These detectors can also operate at room temperature with exceedingly low dark-background count rates and can even match the performance of curved optical focal planes.
The objective of this SAT project is to exploit the developments in atomic layer deposited (ALD) MCPs, ultraviolet detection with high sensitivity photocathodes, and XS image readout techniques to provide a new generation of enhanced-performance, sealed-tube, photon-counting sensors that span the 115-nm to 400-nm wavelength range. The key to this effort is to demonstrate integration of XS readouts into sealed vacuum devices along with ALD MCPs. The final goal is to implement a robust, high-performance sensor that is advanced to Technology Readiness Level-6—i.e., demonstrated in a relevant environment.
“The development of these large area MCP detectors in the UV-Vis is an important enabling technology for the success of future missions like LUVOIR-LUMOS and HabEx-UVS.” - PI, Dr. Oswald Siegmund
Initial work in the first year of the project has successfully demonstrated the construction of XS ceramic anodes that are capable of very high-resolution imaging. Trials also show that they can be hermetically sealed to the final sensor enclosure. Preliminary ALD MCPs with 20-μm and 10-μm channel pore sizes have also been developed. These ALD MCPs show very low background noise characteristics and have already achieved the team’s spatial resolution performance goals. Preliminary processing of ALD MCPs into sealed tube enclosures has been accomplished by our industry partner. The initial data demonstrates that the ALD MCPs suffer no loss of performance subsequent to this integration. Indeed, the post-processing tests with the sealed devices demonstrate better amplification statistics and a high degree of uniformity across the sensor active area. Photocathode deposition trials are also underway. The first tests show state-of-the-art sensitivity at short wavelengths. The trials also achieve photocathodes with a sharp long-wavelength cutoff that excludes red light, which would otherwise increase the effective background noise.
Further work in optimizing the ALD MCPs and photocathodes is currently underway as a precursor to integrating them into fully functional sealed devices. An upcoming major milestone is complete integration of an XS anode with MCPs and a photocathode in a hermetic sensor body. This Engineering Test Unit will enable us to assess the efficacy of the initial components and processing sequence to meet the sensor performance goals and to optimize the final sensor configuration.
Astrophysics Division’s SAT Program
Dr. Oswald Siegmund, UC Berkeley
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