Synchrotron Radiation Workshop, Rome, 22 October 2004 A novel high resolution, high frame rate detector based on a micro-channel-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

Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 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

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

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

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

Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 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!

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

Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 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)

Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 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 ( 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)

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

Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 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.

Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 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 Nyqvist limit of 55  m pixels)

Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 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. (~ 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).

Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October Electron Detection First test results with beta sources 63 Ni, 67 keV max. Gain ~100k, rear field 1600 V Medipix threshold ~38 ke Tl, 764 keV max.

Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 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.

Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 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 Nyqvist limit and below (for event-by-event centroiding) demonstrated Images presented with both UV and electron sources

Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 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, readout for Cherenkov counter, detector for X-ray microscopes at synchrotron…???

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

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

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

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

Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October GaN UV Photocathodes, Å

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

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

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

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

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

Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October 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)

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

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

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

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

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

Bettina Mikulec Synchrotron Radiation Workshop, Rome, 22 October UV Photon Counting Movie Airforce resolution mask, 100 ms exposures