1 / 37

Noiseless Kilohertz Frame Rate Imaging Detector for Adaptive Optics

This study presents a new wavefront sensor for adaptive optics using a noiseless kilohertz frame rate imaging detector based on microchannel plates read out with the Medipix2 CMOS chip.

npuckett
Download Presentation

Noiseless Kilohertz Frame Rate Imaging Detector for Adaptive Optics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A noiseless kilohertz frame rateimaging detector based onmicrochannel plates read outwith the Medipix2 CMOS chip-A new wavefront sensorfor adaptive optics Bettina Mikulec, A.G. Clark, D. Ferrère, D. La Marra University of Geneva J.B. McPhate, O.H.W. Siegmund, A.S. Tremsin, J.V. Vallerga Space Science Laboratory, University of California J. Clément, C. Ponchut, J.-M. Rigal ESRF Grenoble

  2. Point focus   blur Light rays affected by turbulence Parallel light rays 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 New Developments in Photodetection, Beaune, June 2005 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. Adaptive Optics proposal for a new WFS - Optical Medipix tube New Developments in Photodetection, Beaune, June 2005

  4. Adaptive Optics New Developments in Photodetection, Beaune, June 2005 Example for the enormous improvements using AO (Lick Observatory).

  5. TMT Palomar Hale 5m telescope ESO VLT Gemini South The new generation: adaptive optics on 8-10 m telescopes Summit of Mauna Kea volcano in Hawaii: Subaru 2 Kecks New Developments in Photodetection, Beaune, June 2005 Gemini North And at other places: MMT, VLT, LBT, Gemini South

  6. Adaptive Optics • 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. New Developments in Photodetection, Beaune, June 2005 Shack-Hartmann wavefront sensor

  7. 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 • Many 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. • 1 kHz frame rate (light integration, readout, calculations, send out 5000 signals and ready for new frame); faster than the timescale of the atmospheric turbulences • Very low readout noise (< 3e-) New Developments in Photodetection, Beaune, June 2005 • Large pixel array, high frame rate and no readout noise • currently not simultaneously achievable with CCDs!

  8.   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 - integrated into a vacuum tube New Developments in Photodetection, Beaune, June 2005 ITT Industries

  9. 12.7 mm 34 mm Tube Fabrication GaAs photo- cathode • Design finished • Ceramics chip carrier (= tube backend) received from fabrication • Bonding tests underway New Developments in Photodetection, Beaune, June 2005 MCP pair Medipix2 chip

  10. The Medipix2 Photon Counting Chip single pixel: • 256 x 256 pixel array (pixel size 55 µm square) • Amplify, discriminate, gate and count in 14-bit counter per pixel (count rate: ~1 MHz/pixel = 0.33 GHz/mm2) • Readout is digital -> noiseless and fast (266 µs / frame) • 3-side buttable -> 512 x 512 pixel array New Developments in Photodetection, Beaune, June 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 • A standard UV Hg pen-ray lamp with collimator New Developments in Photodetection, Beaune, June 2005

  12. Feasibility Tests • Event size function of MCP gain, rear field, MCP-Medipix distance and Medipix threshold 06 April 2004 single photon events New Developments in Photodetection, Beaune, June 2005 gain 106, rear field 427 V gain 50k, rear field 980 V It works!

  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. New Developments in Photodetection, Beaune, June 2005 take 2 independent uniform illuminations (flood fields at ~500Mcps) Ratio = flood1 / flood2. Histogram of ratio consistent with counting statistics (rms 0.02)

  14. Resolution • The Air Force test pattern was used to demonstrate the imaging properties of the detector, in particular the resolution. increase shutter time New Developments in Photodetection, Beaune, June 2005 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. UV Photon Counting Movie New Developments in Photodetection, Beaune, June 2005 Air Force resolution mask, 100 ms exposures

  16. Spot Size vs. Gain Pinhole grid mask (pitch 0.5 mm x 0.5 mm) to simulate Shack-Hartmann spots: New Developments in Photodetection, Beaune, June 2005 Rear field: 1600V, gap 500 m, threshold ~3 ke- Gain: 200 000 Gain: 20 000

  17. Lamp Pinhole Detector Sub-Pixel Spatial Linearity New Developments in Photodetection, Beaune, June 2005

  18. Average Movement of ~700 Spots 1 pixel New Developments in Photodetection, Beaune, June 2005 • Achieved a 2 m rms centroid position error with ~550 events/spot.

  19. 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. Gain ~60k, rear field 1600 V Medipix threshold ~38 ke- New Developments in Photodetection, Beaune, June 2005 63Ni, 67 keV max. ~300 counts/pixel 204Tl, 764 keV max. ~100 counts/pixel

  20. 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 • Measured dynamic range: ~1 cps to 500M cps • Images presented with both UV and electron sources  detector has a great capacity to be used for various wavelengths and particles New Developments in Photodetection, Beaune, June 2005

  21. Ongoing work • Test new ceramic chip carrier (= tube backend); thermal cycling tests with Medipix2 chip mounted • Tube fabricationat commercial firm (with bi-alkali and GaAs photo-cathode) • Test prototype parallel readout board designed at ESRF • reduce output bandwidth by using an FPGA; goal: 1 kHz continuous frame rate with a 2x2 chip arrangement • Test prototype tubes at the AO laboratory at CFAO, U.C. Santa Cruz • Final test at a telescope New Developments in Photodetection, Beaune, June 2005

  22. Backup Slides! New Developments in Photodetection, Beaune, June 2005

  23. 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. centroiding New Developments in Photodetection, Beaune, June 2005 Group 4-2 starts to be resolved (17.95 lp/mm; 55.7 m corresponding to ~28 m pixels). Could be useful for low rate imaging applications!

  24. Parallel Readout Board • Successful review of the new parallel readout board PRIAM in May • Five 32-bit parallel input ports to read out up to 5 Medipix2 chips in <290 s (clock 100 MHz) • XILINX FPGA for data arrangement, optional flat field and dead time correction as well as data reduction (e.g. spot coordinates) • Provides all control signals and voltages • 4 bi-directional 1.6 Gbit/s links  total data output time 660 s New Developments in Photodetection, Beaune, June 2005

  25. The Setup at SSL - Photos New Developments in Photodetection, Beaune, June 2005

  26. Spot Size New Developments in Photodetection, Beaune, June 2005 Spot area versus Medipix2 low threshold. Spot area versus rear field.

  27. Soft X-Ray Photocathodes New Developments in Photodetection, Beaune, June 2005

  28. EUV and FUV New Developments in Photodetection, Beaune, June 2005

  29. GaN UV Photocathodes, 1000- 4000Å New Developments in Photodetection, Beaune, June 2005

  30. h Isoplanatic Angle (0) & Sky Coverage Bright stars + 0 =1% sky coverage New Developments in Photodetection, Beaune, June 2005 Telescope Primary mirror

  31. Laser Guide Stars Can achieve>70% skycoverage withlaserguidestaradaptive optics! New Developments in Photodetection, Beaune, June 2005

  32. 589.2 nm L d Laser Guide Star Parallax • “Star” more of a streak • Shape changes over pupil • Can use pulsed laser to limit spatial extent • Requires gated detector New Developments in Photodetection, Beaune, June 2005

  33. Advantages of Multi-Pixel Sampling of Shack Hartmann Spots New Developments in Photodetection, Beaune, June 2005 5 x 5 2 x 2 • Linear response off-null • Insensitive to input width • More sensitive to readout noise

  34. Deformable Mirrors • Range from 13 to > 900 actuators (degrees of freedom) ~ 300mm New Developments in Photodetection, Beaune, June 2005 ~ 50 mm Xinetics

  35. Position Error (550 Events/Spot) rms = 2.0 µm New Developments in Photodetection, Beaune, June 2005

  36. Medipix readout of semiconductor arrays New Developments in Photodetection, Beaune, June 2005

  37. X-ray of Fish (… with silicon detector) New Developments in Photodetection, Beaune, June 2005

More Related