Photon Counting Sensors for Future Missions Dr. Oswald Siegmund Space Sciences Laboratory University of California, Berkeley, CA Spectroscopy Imaging M31/32 FUSE rowland circle 200 x 10mm curved MCP detector, 10k x 300 format GALEX 65mm MCP sealed detectors, 2k x 2k format 130nm -300nm

Historical Progress of Spatial Resolution for photon counting sensors Imaging and spectroscopy MCP sensors for past and future missions. All science topics show rapid rise in spatial resolution performance requirements. Astronomy/solar sensors are most demanding. Remote sensing less so but have greater timing needs. Planetary sensors emphasize low power/weight

Photon Counting Sensor Characteristics No need for accurate pointing stability during long exposures No cosmic ray streaks Photons time tagged, rebin image with aspect solution Cosmic rays rejected, or just dots. No radiation damage. No degradation of cathode QE with time or environment No transfer of blank data areas, no noise pedestal No cooling required. No need for de-contamination. No CTE changes Only photon events and photon-like background registered

Microchannel Plate Detectors Photocathodes convert radiation (photons, particles) Amplify signal with microchannel plates Register position and time with electronic readout Detector Capabilities Sizes up to >100mm QE, 60% max (FUV) High timing resolution, <100ps High spatial resolution, <10µm High event rates, >MHz Low background, 0.02 cm-2 sec-1 Schematic for cross strip readout

High Quantum Efficiency Photocathodes New III-V photo-cathodes are under development & significant improvements in QE are being made STIS QE @ 600nm < 10-6 GaN opaque photocathodes show high QE and longevity GaAs photocathodes overlap GaN and have high QE into IR Other materials also show promise, diamond, othe III-V compounds

Advanced Microchannel Plates Photo-lithographic silicon based MCP’s - uniform pore pattern. No multifiber boundaries & array distortions of glass MCP’s. Large substrate sizes (100mm) OK, with small pores (<5µm). High temperature tolerance - CVD cathode processes OK. Initial tests are encouraging, but needs more development Diamond on Si MCP Ultra low background rates <0.02 events cm-2 sec-1 8cm Si MCP on 100mm wafer Si MCP ~7um hex pores, >75% OAR

Cross Strip Imaging Readout Anodes 32 x 32mm have been made. Cross strip is a multi-layer cross finger layout. Event charge centroid gives event positions. Ultra high spatial resolution (<5µm) Large formats possible (100mm) in many shapes Low gain/long lifetime/low fixed pattern noise Gain 4 x 105 7µm pore MCP pair at 2x106 gain ASIC preamps plug directly to the anode Air force mask on 7µm pore MCP pair with 32mm cross strip

MEDIPIX (CMOS) readout for MCP’s 1 kHz frame rate noiseless photon counter with GHz counting rate Cathode + MCP + image readout using “Medipix2” ASIC by CERN. 55um pixel @ 256x256 (3-side buttable), 14mm x 14mm CMOS chip . Pixel level amp, discriminator, gate & counter, to count photon events. MCP gain only 104, CMOS noise negligible. Very high dynamic range. Events counted at each pixel for each frame - (No charge transfer). MCP testbed built, Medipix imaging @ 500MHz rates, 55µm resolution. Single frame shows single photons Integration shows image resolution MEDIPIX in MCP housing

Photon Counting Sensor Prospects QE >50% over 10nm - 900nm range, in selectable bandpasses, with solar blind options. Si MCP’s with <5um pores, low fixed pattern noise, low background <0.02 cm-2 sec-1 & lifetimes 100 - 1000x better. Cross strip readouts with 20k x 20k resolution, selectable format sizes up to >100 x 100mm, & counting rates >10 MHz, with 100x improved local rates CMOS, MEDIPIX, readouts with GHz rates, 1k x 1k abuttable to 2k x 2k with <25um pixels.