photon counting detectors for sub-millisecond astronomy

2nd Zwicky Informal Workshop - Berkeley 2005

May 26, 2005John Vallerga

John Vallerga, Barry Welsh, Anton Tremsin, Jason McPhate and Oswald Siegmund

Experimental Astrophysics Group

Space Sciences Laboratory

University of California, Berkeley

Photon counting detectors for sub-millisecond astronomy



• Over 20 UV detectors in space

• Active R&D program

• Expanding to ground based applications– Astronomy

– Biology

– Physics

EAG specializes in photon counting MCP Detectors

25 mm Optical Tube

GALEX NUV Tube

68 mm

FUSE and COS FUV for HST (2007??)

200 mm



Imaging, Photon Counting DetectorsCharge distribution on stripsCharge CloudMCP stackTube Window withphotocathodeγ

Photocathode converts photon to electron

MCP(s) amplify electron by 104 to 108

Rear field accelerates electrons to anode

Patterned anode measures charge centroid



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)



GaAs Photocathodes (GenIII)

• Developed for night vision tubes

• Can be enhanced for Blue and near IR

• Slight cooling required (104 cps at room temp)



Readout Anodes

Delay Line Medipix ASICCross Strip

Input

Preamp

Disc.

Disc. logic Mux. 13 bit

counter –ShiftRegister

Clock out

Shutter

Lower Thresh.

Disc.

Mux.

Previous Pixel

Mask bit

Analog Digital

Upper Thresh.

Next Pixel

Mask bit

Polarity



Readout Anode PerformanceType Format

(resels)Spatial resolution

Temporal resolution

Event rate

Delay Line

20482 20µm FWHM

50 ps 2 MHz

Cross Strip

10k2 9 µm FWHM

50 ps 5 MHz

Pixelated ASIC

2562 55 µm pixels

1 ms 2 GHz



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



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)



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



Wavefront Sensors for Large Telescopes

• GaAs image tube

• Medipix readout

• 1000 frames/sec

• 5000 centroids/frame

• 1000 events/centroid

• 5 GHz ct rate

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.



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



Flares

QuickTime™ and aGIF decompressor

are needed to see this picture.

NUV

FUV



Debris and satellite movies



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



Spatial Resolution (cont’d)

12 µm pore glass MCPs 7 µm pore glass MCPs

Cross Strip readout of Glass MCPs

photon counting detectors for sub-millisecond astronomy

Documents