1. CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 Photon Counting with a 512 x 512 Pixel Array at 1 kHz Frame Rate - A New Wavefront Sensor for Adaptive Optics Bettina Mikulec, Allan Clark University of Geneva John Vallerga, Jason McPhate, Anton Tremsin, Oswald Siegmund Space Science Laboratory, University of California

2. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 2 Introduction into Adaptive Optics* 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 –Temperature fluctuations in the air cause changes in the index of refraction –light rays are no longer parallel when they reach telescope and can therefore not anymore be focused to 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  blur  Point focus Parallel light rays Light rays affected by turbulence

3. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 3 Adaptive Optics proposal for a new WFS - Optical Medipix tube

4. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 4 Example for the enormous improvements using AO (Lick Observatory). Adaptive Optics

5. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 5 The new generation: adaptive optics on 8-10 m telescopes Summit of Mauna Kea volcano in Hawaii: Subaru 2 Kecks Gemini North And at other places: MMT, VLT, LBT, Gemini South ESO VLT Gemini South

6. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 6 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 Palomar Hale 5m telescope Next Generation of Large Telescopes (proposed) TMT

7. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 7 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

8. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 8 Wavefront Sensor Requirements High QE for dimmer guide stars (~80% optical QE) Gate the detector in 2-4  s range for operation with laser guide stars 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); faster than the timescale of the atmospheric turbulences oVery low readout noise (< 3e - ) Large pixel array, high frame rate and no readout noise not simultaneously achievable with CCDs!

9. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 9 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  Integrate photon events on pixel, noiseless chip readout

10. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 10 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)

11. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 11 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)

12. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 12 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

13. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 13 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.

14. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 14 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)

15. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 15 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).

16. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 16 UV Photon Counting Movie Air Force resolution mask, 100 ms exposures

17. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 17 Spot Size vs. Gain Pinhole grid mask (pitch 0.5 mm x 0.5 mm) to simulate Shack- Hartmann spots: Rear field: 1600V, gap 500  m, threshold 3 ke - Gain: 200 000Gain: 20 000

18. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 18 Sub-Pixel Spatial Linearity Lamp Pinhole Detector

19. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 19 Average Movement of ~700 Spots 1 pixel Achieved a 2  m rms centroid position error with ~550 events/spot.

20. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 20 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

21. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 21 Conclusions New detector concept proven to work! Performed systematic tests varying different detector parameters 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

22. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 22 Ongoing work Test new ceramic chip carrier (= tube backend); thermal cycling tests with Medipix2 chip mounted Tube fabrication at SSL Berkeley and at commercial firm with GaAs photo-cathode Test prototype parallel readout board 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, 1.5 more years to go…, some funding for Univ. Geneva from Fonds National and F. Schmidheiny Consider other applications for such a detector

23. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 23 Parallel Readout Board

24. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 24 Tube Design

25. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 25 Tube Design

26. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 26 Backup Slides!

27. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 27 The Setup at SSL - Photos

28. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 28 Spot Size Spot area versus rear field. Spot area versus Medipix2 low threshold.

29. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 29 Soft X-Ray Photocathodes

30. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 30 EUV and FUV

31. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 31 GaN UV Photocathodes, 1000- 4000Å

32. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 32 h Bright stars +  0 = 1% sky coverage Isoplanatic Angle (  0 ) & Sky Coverage Telescope Primary mirror

33. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 33 Laser Guide Stars Can achieve >70% sky coverage with laser guide star adaptive optics!

34. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 34 Laser Guide Star Parallax “Star” more of a streak Shape changes over pupil Can use pulsed laser to limit spatial extent Requires gated detector

35. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 35 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

36. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 36 Deformable Mirrors Range from 13 to > 900 actuators (degrees of freedom) Xinetics ~ 50 mm ~ 300mm

37. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 37 Position Error (550 Events/Spot) rms = 2.0 µm

38. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 38 Medipix readout of semiconductor arrays

39. Bettina Mikulec CHIPP Astro-Particle Physics Workshop, Versoix, May 3 rd 2005 39 X-ray of Fish (… with silicon detector)