Photon counting detectors for sub-millisecond astronomy

1. Photon counting detectors for sub-millisecond astronomy John Vallerga, Barry Welsh, Anton Tremsin, Jason McPhate and Oswald Siegmund Experimental Astrophysics Group Space Sciences Laboratory University of California, Berkeley

2. FUSE and COS FUV for HST (2007??) 200 mm 25 mm Optical Tube GALEX NUV Tube 68 mm EAG specializes in photon counting MCP Detectors • Over 20 UV detectors in space • Active R&D program • Expanding to ground based applications • Astronomy • Biology • Physics

3. Photocathode converts photon to electron MCP(s) amplify electron by 104 to 108 Rear field accelerates electrons to anode Patterned anode measures charge centroid Imaging, Photon Counting Detectors

4. Why would you want one? • No readout noise penalty • Use as many pixels as you wish • Continuous temporal sampling to ~ nsecs • Choose integration period(s) after the fact or on the fly • Other advantages • Selectable bandpass from soft xray to optical • Large area, curved focal planes • Cosmic ray = 1 count • LN2 not required • Low dark current (0.16 attoamps cm-2)

5. GaAs Photocathodes (GenIII) • Developed for night vision tubes • Can be enhanced for Blue and near IR • Slight cooling required (104 cps at room temp)

6. Readout Anodes Delay Line Cross Strip Medipix ASIC

7. Readout Anode Performance

8. Photon Counters over CCDs • Where read noise dominates sky-noise • High speed spectro-photometry • When CCD readout time is longer than integration time of interest • Pulsars • Flare Stars and CVs • Short Transients • Wavefront sensors for adaptive optics • Kilohertz rates supporting many actuators

9. Current projects • GaAs optical image tube for high speed imaging/polarimetry of pulsars (NSF) • Optical wavefront sensor detector (NOAO) • On-going analysis of GALEX transient data (NASA) • Detection of space debris with LANL • Biological fluorescence lifetime imaging (NIH)

10. Detector for High Speed Polarimeter • Redfren and Shearer, National Univ. of Ireland, Galway • Goal is to measure all 4 Stokes parameters per pulse of the Crab simultaneously at 100 µs temporal resolution • Imaging required to optimize aperture and properly subtract background

11. Wavefront Sensors for Large Telescopes • GaAs image tube • Medipix readout • 1000 frames/sec • 5000 centroids/frame • 1000 events/centroid • 5 GHz ct rate

12. GALEX Transient Survey • NUV and FUV detectors, 45 cm telescope • 1.5° FOV • 5 millisec. resolution • 84 objects found in 1st year • RR Lyrae, dMe flares, SXRTs • GJ 3685 dM4e had a 12 mag increase in 200 sec. • Satellites and space debris

13. Flares NUV FUV

14. Debris and satellite movies

15. Summary • Imaging, photon counting detectors have a place in ground based astronomy, especially for fast transients • As the QE increases, so do the niche applications • Our new vacuum tube is designed to easily integrate into an industrial production line • “Application Specific” detectors

17. Spatial Resolution (cont’d) Cross Strip readout of Glass MCPs 12 µm pore glass MCPs 7 µm pore glass MCPs