High performance microchannel plate detectors for UV/visible Astronomy

1. High performance microchannel plate detectors for UV/visible Astronomy Dr. O.H.W. Siegmund Space Sciences Laboratory, U.C. Berkeley Work funded by NASA grants, NAG5-8667, NAG5-11547, NAG-9149

2. Advanced MCP Sensors for AstrophysicsExisting Detectors High QE alkali halide cathodes (CsI, KBr) with ~50%QE covering 10nm - 185nm MCP’s with 12µm to 6µm pores, background 0. 2 events cm-2 sec-1 Cross-delay line readouts with 15µm resolution, 90 x 20mm, 65mm formats COS 2 x 90mm x 10mm XDL detector GALEX 65mmsealed tube XDL detector

3. Advanced MCP Sensors for AstrophysicsCOS FUV Detector and Electronics

4. Advanced MCP Sensors for AstrophysicsCOS FUV Detector QE CsI cathodes on FUV02 flight detector compared with COS spec Segment B Segment A

5. Advanced MCP Sensors for AstrophysicsCOS Detector Event Rate Performance COS FUV local and global count rate performance is better than FUSE, and exceeds specs. Global count rate throughput

6. COS detector co-added image of 10µm pinholes on 500µm centers & 25µm x 500µm slits 200µm apart. Pixels are 6µm x 25µm or ~15,000 x 400 format per segment. Advanced MCP Sensors for AstrophysicsCOS Detector Resolution COS FUV detector resolutionis ~20µm x 30µm FWHM

7. Advanced MCP Sensors for AstrophysicsDeveloping Detector Prospects Raw flat field image Shows MCP multi -fibers, but after thermal correction and division data looks statistical (with~4400 cnts/resel we get S/N ~60:1). Using FPSPLIT with 4 co-added images each with 60:1 S/N we get S/N of ~100:1 which is in close accord with photon statistics. For analysis see memoby Wilkinson/Penton/Vallerga/McPhate.

8. Photocathode Development GaAs Photocathodes on windows, & Diamond Photocathodes on Silicon & Si MCP’s Polycrystalline boron doped diamond, band gap - 5.47 eV (227 nm) - Solar blind. Hydrogenated diamond is air stable (<10% drop in 18 hours) and is very robust. GaAs QE up to 50% in the red now possible, low background ≈10 events/sec@-20°C Time response <1ns, for Interferometry, Lidar,Molecular fluorescence. Diamond coated Silicon MCP Cs activated Pre-hydrogenated values GaAs photocathode UV efficiency Diamond Photocathodes on Silicon and Si MCP’s

9. GaN Photocathodes opaque semitransparent Fig.2. Measured QE of GaN samples on sapphire (300µm) after cesiation, for semitransparent (corrected for substrate transmission) & opaque modes Fig.1. Measured quantum efficiency of CsI on MCP’s, CsTe semitransparent (NIST) on MgF2 window and CsTe semitransparent (GALEX) on thick UV silica windows.

10. Silicon MCP’s Silicon MCP’s are made by photo-lithographic methods Photolithographic etch process - very 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 and “hot” processes OK UHV compatible, low background (No radioactivity) Development in collaboration with Nanosciences. Typical Silicon microchannel plates in test program 25mm diameter (75mm currently feasible) 40:1 to 60:1 L/D (>100:1 possible) 7µm pore size, hexagonal and square pore ~2° bias and 8° bias, resistances ~GΩ, to <100MΩ possible Working on processing techniques to improve uniformity Techniques for gain & QE enhancement under investigation Silicon MCP Developments • Hexagonal pore Si MCP with • ~7µm pores, >75% open area 8cm Si MCP on 100mm substrate

11. Silicon MCP Performance Characteristics Gain & PHD very similar to glass MCP’s, stacks of Si MCP’s (4) with gain up to 106 QE is similar to good bare glass MCP’s (COS, EUVE, 12/10/6µm) The background rate is lower (0.02 events cm-2 sec-1) than any glass MCP Gain and response uniformity are reasonably good. No “hex” modulation! 12/10µm COS 6µm pore MCP Contrast enhanced image of the fixed pattern response to a Hg vapor lamp with a stack of 4 Si MCP’s. ~14mm area, 107 counts, ~50µm resolution XDL. QDE for Si & bare glass MCP’s vs Wavelength

12. Cross strip anode readout 32mm x 32mm XS anode, 0.5mm period Cross strip is a multi-layer cross finger layout. Fingers have ~0.5mm period on ceramic. Charge spread over 3-5 strips per axis, Event position is derived from charge centroid. Can encode multiple simultaneous events. Fast event propagation (few ns). Anodes up to 32 x 32mm have been made Signals are routed to anode backside by hermetic vias Packaging can be compact with amp on anode backside Overall processing speed should support >> MHz rates Compact and robust (900°C). Bottom fingers

13. Cross Strip Anode Electronics Chain Basic encoding sequence Small, low power ASIC encoding with sparsification reduces data throughput requirements Cross strip anode position encoding electronics test-bed system. All signals amplified and digitized. Can choose up to 12 bits per signal. Anode backside showing the external board where preamplifier chips are mounted.

14. Cross Strip Anode Readout Outstanding Spatial Resolution/Linearity ~7µm pores are resolved, <3 µm electronic resolution with 10 bit encoding electronics Image linearity is ~1µm level and shows pore misalignments and multi-fiber boundaries Gain required is <4 x 105, allows higher local event rates than normal readouts Lower gain means longer overall MCP lifetime due to reduced charge extraction. Small zone of a single 12µm 160:1 L/D MCP at 2x105 gainshowing apparent displacement of pore images at multifiber boundaries Flood image of 12µm pore MCP pair at 4 x 106 Gain, ≈1mm square area.

15. Resolution of Cross Strip MCP Sensors Gain 1.3 x 106 Air force mask on 6µm pore MCP pair with cross strip readout Air force mask on Single 6µm pore MCP optical image

16. Near-UV Channel 60mm XDL detectors with CsI and CsTe photocathodes, Launched 6/03 Advanced MCP Sensors for AstrophysicsGALEX Early Observations M101 M83

17. Ultraviolet GALEX Visible DSS Near Infrared 2MASS M51 – Whirlpool GalaxyComparison GALEX Early Data

18. M31 Andromeda