1. 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

3. 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

4. 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

5. 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

6. High Quantum Efficiency Photocathodes
New III-V photo-cathodes are under development
& significant improvements in QE are being made
STIS
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

7. 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

8. 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

9. 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 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 500MHz rates, 55µm resolution.
Single frame shows
single photons
Integration shows
image resolution
MEDIPIX in MCP housing

10. 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 x 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.