1. Synchrotron Radiation Workshop, Rome, 22 October 2004 A novel high resolution, high frame rate detector based on a microchannel plate read out with the Medipix2 counting CMOS pixel chip Bettina Mikulec, Allan Clark University of Geneva John Vallerga, Jason McPhate, Anton Tremsin, Oswald Siegmund Space Science Laboratory, University of California

2. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 2 Introduction* Turbulence in the earth’s atmosphere makes stars twinkle More importantly, turbulence spreads out the star light making it a blob rather than a point Even the largest ground-based astronomical telescopes have no better resolution than an 8" telescope! Even the largest ground-based astronomical telescopes have no better resolution than an 8" telescope! *adapted from AO lectures of Claire Max, Astro289C, UC Santa Cruz

3. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 3 Adaptive Optics  blur  Point focus Parallel light rays Light rays affected by turbulence proposal for a new WFS - Optical Medipix tube

4. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 4 Example for the enormous improvements using AO (Lick Observatory). Adaptive Optics

5. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 5 Determine the distortions with the help of a natural or laser guide star and a lenslet array (one of the methods). Deviations of the spot positions from a perfect grid is a measure for the shape of the incoming wave-front. Adaptive Optics Shack-Hartmann wavefront sensor

6. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 6 Wavefront Sensor Requirements High QE for dimmer guide stars (~80% optical QE) oMany pixels in the order of 512 x 512; future large telescopes will have about 5000 actuators (controlled via 70 x 70 centroid measurements) 1000 photons per spot to get a 3% centroid rms error with respect to the stellar image size. o1 kHz frame rate (light integration, readout, calculations, send out 5000 signals and ready for new frame) corresponding to the timescale of the atmospheric turbulences oVery low readout noise (< 3e - ) Gate the detector in 2-4  s range for operation with laser guide stars Large pixel array, high frame rate and no readout noise not simultaneously achievable with CCDs!

7. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 7 2 µm pores on 3 µm centers (Burle Industries)    Proposal for a New Wavefront Sensor  High-QE GaAs photo-cathode  Matched pair of microchannel plates (MCP) with 10  m pore diameter in chevron configuration  Medipix2 counting CMOS pixel chip  Noiseless chip readout

8. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 8 The Medipix2 Photon Counting Chip  0.25  m CMOS technology (33M transistors/chip)  square pixel size of 55 µm  256 x 256 pixels  sensitive to positive or negative input charge (free choice of different detector materials)  pixel-by-pixel detector leakage current compensation  window in energy  discriminators designed to be linear over a large range  14-bit counter per pixel  count rate: ~1 MHz/pixel (0.33 GHz/mm 2 )  3-side buttable  serial or parallel I/O (min. readout time of full matrix 266 µs)

9. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 9 Measurement Setup A Medipix2 photon counting chip A matched pair of MCPs: –Photonis MCPs with 33 mm diameter –10  m hole diameters, L/D = 40/1 –low resistivity (~22 MOhms per plate) –gain was varied between 20k and 200k (1430 - 1680 V) Vacuum tank pumped down to ~10 -6 torr Hermetic feed-throughs (50-pin connector for Medipix signals) A standard UV Hg pen-ray lamp with collimator (~10 counts/s -500M counts/s)

10. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 10 Feasibility Tests single photon events gain 10 6, rear field 427 Vgain 50k, rear field 980 V It works! 06 April 2004 Event size function of MCP gain, rear field, MCP-Medipix distance and Medipix threshold

11. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 11 Flood Fields Take image with collimated UV source at 50ke gain and 1600 V rear field (~5000 counts/pixel). Average single spot area: 2.4 pixels –Fixed pattern noise from dead spots on the MCPs and MCP multifibres divides out. take 2 independent uniform illuminations (flood fields at ~500Mcps) Histogram of ratio consistent with counting statistics (rms 0.02) Ratio = flood1 / flood2.

12. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 12 Resolution The Air Force test pattern was used to demonstrate the imaging properties of the detector, in particular the resolution. increase shutter time 100  s exposure; the spots correspond to individual photon events. 1 s exposure.Group 3-2 visible (~9 lp/mm corresponding to the Nyquist limit of 55  m pixels)

13. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 13 Event Centroiding Centroiding individual photon events to achieve sub-pixel resolution: –Take many very low count rate images with larger spot area to avoid overlapping spots. (~100-150 counts/frame; 1000 frames) –Identify unique spots and reject overlapping events (counts  2), count spots, record their size and calculate the centroids. Could be useful for low rate imaging applications! centroiding Group 4-2 starts to be resolved (17.95 lp/mm; 55.7  m corresponding to ~28  m pixels).

14. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 14 UV Photon Counting Movie Air Force resolution mask, 100 ms exposures

15. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 15 Electron Detection First test results with beta sources  QE ~46% for Ni and ~63% for the Tl image; increasing efficiency with e - energies above ~50 keV consistent with literature. 63 Ni, 67 keV max. ~300 counts/pixel Gain ~60k, rear field 1600 V Medipix threshold ~38 ke - 204 Tl, 764 keV max. ~100 counts/pixel

16. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 16 Conclusions New detector concept proven to work! Systematic tests varying different detector parameters underway No fixed pattern noise yet detectable except MCP imperfections Resolution at Nyquist limit and below (for event-by-event centroiding) demonstrated Images presented with both UV and electron sources  detector has a great capacity to be used for various wavelengths and particles

17. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 17 Future Plans Tube fabrication at SSL Berkeley and at commercial firm; finalize ceramic chip carrier design Specific parallel readout board to be designed in collaboration with ESRF; reduce output bandwidth by using an FPGA; goal: 1 kHz continuous frame rate with 2x2 chip arrangement Test prototype tubes at the AO laboratory at CFAO, U.C. Santa Cruz Final test at a telescope SSL received 3-year NOAO grant, 2 more years to go… Are there other applications for such a detector? –Beam monitor for hadron therapy, readout for Cherenkov counter, detector for X-ray microscopes at synchrotron…???

18. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 18 Backup Slides!

19. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 19 The Setup at SSL - Photos

20. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 20 Soft X-Ray Photocathodes

21. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 21 EUV and FUV

22. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 22 GaN UV Photocathodes, 1000- 4000Å

23. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 23 h Bright stars +  0 = 1% sky coverage Isoplanatic Angle (  0 ) & Sky Coverage Telescope Primary mirror

24. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 24 Laser Guide Stars Can achieve >70% sky coverage with laser guide star adaptive optics!

25. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 25 Laser Guide Star Parallax “Star” more of a streak Shape changes over pupil Can use pulsed laser to limit spatial extent Requires gated detector

26. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 26 Advantages of Multi-Pixel Sampling of Shack Hartmann Spots  Linear response off-null  Insensitive to input width  More sensitive to readout noise 2 x 2 5 x 5

27. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 27 Deformable Mirrors Range from 13 to > 900 actuators (degrees of freedom) Xinetics ~ 50 mm ~ 300mm

28. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 28 30 m diameter: –California Extremely Large Telescope (CELT) - –Thirty Meter Telescope (TMT) 50 m diameter: –EURO50 on La Palma 100 m diameter: –European Southern Observatory’s “OverWhelmingly Large Telescope” (OWL) All propose AO systems with > 5000 actuators Next Generation of Large Telescopes (proposed)

29. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 29 collection of secondary electrons (SE) emitted by 0.1 – 0.4  m aluminum ( Al-Al 2 O 3 -Al) foils (G. Molinari, CERN) Electron Detection One example for different application than AO: Beam monitor for hadron therapy slide from W. Dulinsky, presented at IWORID2004 Glasgow; SUCIMA project.

30. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 30 Sub-Pixel Spatial Linearity Lamp Pinhole Detector

31. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 31 Average Movement of 700 Spots 1 pixel

32. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 32 Position Error (550 Events/Spot) rms = 2.0 µm

33. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 33 Spot Size Spot area versus rear field. Spot area versus Medipix2 low threshold.

34. Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 2004 34 X-ray of Fish (… with silicon detector)