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
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
• 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
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
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
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
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)
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
GaAs Photocathodes (GenIII)
• Developed for night vision tubes
• Can be enhanced for Blue and near IR
• Slight cooling required (104 cps at room temp)
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
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
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
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
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
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
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
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)
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
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
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
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.
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
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
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
Flares
QuickTime™ and aGIF decompressor
are needed to see this picture.
NUV
FUV
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
Debris and satellite movies
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
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
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
2nd Zwicky Informal Workshop - Berkeley 2005
May 26, 2005John Vallerga
Spatial Resolution (cont’d)
12 µm pore glass MCPs 7 µm pore glass MCPs
Cross Strip readout of Glass MCPs