IWORID 2004 Glasgow - J. Vallerga John Vallerga, Jason McPhate, Anton Tremsin and Oswald Siegmund Space Sciences Laboratory, University of California, Berkeley Bettina Mikulec and Allan Clark University of Geneva Optically sensitive Medipix2 detector for adaptive optics in very large telescopes

IWORID 2004 Glasgow - J. Vallerga Adaptive optics tutorial* Turbulence in earth’s atmosphere makes stars twinkle More importantly, turbulence spreads out light; makes it a blob rather than a point Even the largest ground-based astronomical telescopes have no better resolution than a 20 cm telescope! Even the largest ground-based astronomical telescopes have no better resolution than a 20 cm telescope! *Adapted from AO lectures of Claire Max, Astro 289C, UC Santa Cruz

IWORID 2004 Glasgow - J. Vallerga Optical consequences of turbulence Temperature fluctuations in small patches of air cause changes in index of refraction (like many little lenses) Light rays are refracted many times (by small amounts) When they reach telescope they are no longer parallel Hence rays can’t be focused to a point: Parallel light raysLight rays affected by turbulence  blur  Point focus

IWORID 2004 Glasgow - J. Vallerga How a deformable mirror works (idealization) BEFORE AFTER Incoming Wave with Aberration Deformable Mirror Corrected Wavefront

IWORID 2004 Glasgow - J. Vallerga Adaptive optics increases peak intensity of a point source Lick Observatory No AO With AO No AO With AO Intensity

IWORID 2004 Glasgow - J. Vallerga Schematic of adaptive optics system Feedback loop: next cycle corrects the (small) errors of the last cycle Optical Medipix tube goes here

IWORID 2004 Glasgow - J. Vallerga Lick adaptive optics system at 3m Shane Telescope Off-axis parabola mirror Wavefront sensor IRCAL infra- red camera DM

IWORID 2004 Glasgow - J. Vallerga How to measure turbulent distortions (one method among many) “Shack-Hartman” WFS

IWORID 2004 Glasgow - J. Vallerga 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

IWORID 2004 Glasgow - J. Vallerga Neptune in infra-red light (1.65 microns) Without adaptive optics With Keck adaptive optics June 27, arc sec May 24, 1999

IWORID 2004 Glasgow - J. Vallerga VLT NAOS AO first light Cluster NGC 3603: IR AO on 8m ground-based telescope achieves same resolution as HST at 1/3 the wavelength Hubble Space Telescope WFPC2, = 800 nm NAOS AO on VLT = 2.3 microns

IWORID 2004 Glasgow - J. Vallerga Faint companions around bright stars Two images from Palomar of a brown dwarf companion to GL 105 Credit: David Golimowski End Tutorial

IWORID 2004 Glasgow - J. Vallerga Vision Science End Tutorial

IWORID 2004 Glasgow - J. Vallerga 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)

IWORID 2004 Glasgow - J. Vallerga WFS detector requirements High optical QE for dimmer guide stars Lots of pixels - eventually 512 x 512 Very low readout noise kHz frame rates The last three are not simultaneously achievable with the current generation of CCDs

IWORID 2004 Glasgow - J. Vallerga MCP Detectors at SSL Berkeley COS FUV for Hubble (200 x 10 mm windowless) 25 mm Optical Tube GALEX 68 mm NUV Tube (in orbit)

IWORID 2004 Glasgow - J. Vallerga Imaging, Photon Counting Detectors Photocathode converts photon to electron MCP(s) amplify electron by 10 4 to 10 8 Rear field accelerates electrons to anode Patterned anode measures charge centroid

IWORID 2004 Glasgow - J. Vallerga GaAs Photocathodes (GenIII) Photocathode type determines wavelength response Soft x-ray to near IR

IWORID 2004 Glasgow - J. Vallerga Wavefront Sensor Event Rates (example for big telescope) 5000 centroids Kilohertz feedback rates (atmospheric timescale) 1000 detected events per spot for sub-pixel centroiding  5000 x 1000 x 1000 = 5 Gigahertz counting rate! Requires integrating detector

IWORID 2004 Glasgow - J. Vallerga Our concept An optical imaging tube using: –GaAs photocathode –Microchannel plate to amplify a single photoelectron by 10 4 –Bare Medipix2 to count these events per pixel

IWORID 2004 Glasgow - J. Vallerga Vacuum Tube Design

IWORID 2004 Glasgow - J. Vallerga Vacuum Tube Design

IWORID 2004 Glasgow - J. Vallerga Vacuum Tube Design

IWORID 2004 Glasgow - J. Vallerga Vacuum Tube Design

IWORID 2004 Glasgow - J. Vallerga First test detector Demountable detector Simple lab vacuum, no photocathode Windowless – UV sensitive

IWORID 2004 Glasgow - J. Vallerga Initial Results It Works! First light! Lower gain, higher rear field

IWORID 2004 Glasgow - J. Vallerga MCP event spot area

IWORID 2004 Glasgow - J. Vallerga MCP charge cloud size

IWORID 2004 Glasgow - J. Vallerga Spatial Resolution 100 µs1 s Group 3-2 visible 9 lp/mm = 55µm (Nyquist limit)

IWORID 2004 Glasgow - J. Vallerga Interesting tangent - sub pixel resolution Use single spot events and calculate centroids Accumulate event x,y list 2-d histogram on finer pitch 9 lp/mm

IWORID 2004 Glasgow - J. Vallerga Interesting tangent - sub pixel resolution Calculate centroids of each event Accumulate event x,y list 2-d histogram on finer pitch 16 lp/mm

IWORID 2004 Glasgow - J. Vallerga Flat Field 1200 cts/bin - 500Mcps MCP deadspots Hexagonal multifiber boundaries

IWORID 2004 Glasgow - J. Vallerga Flat Field (cont) Histogram of Ratio consistent with counting statistics (2% rms) Ratio Flat1/Flat2

IWORID 2004 Glasgow - J. Vallerga Future Work (3 yr. NOAO grant) Optimize MCP-Medipix2 interface design Design and build tube with Medipix2 and GaAs Develop parallel readout with European collaborators Develop FPGA to reduce output bandwidth –5 million centroids/s vs. 262 million pixels/s. Test at AO laboratory at CFAO, U.C. Santa Cruz Test at telescope

IWORID 2004 Glasgow - J. Vallerga Acknowledgements Univ. of Barcelona University of Cagliari CEA CERN University of Freiburg University of Glasgow Czech Academy of Sciences Mid-Sweden University University of Napoli NIKHEF University of Pisa University of Auvergne Medical Research Council Czech Technical University ESRF University of Erlangen-Nurnberg Thanks to the Medipix Collaboration: This work was funded by an AODP grant managed by NOAO and funded by NSF

IWORID 2004 Glasgow - J. Vallerga Soft X-Ray Photocathodes

IWORID 2004 Glasgow - J. Vallerga EUV and FUV

IWORID 2004 Glasgow - J. Vallerga GaN UV Photocathodes, Å

IWORID 2004 Glasgow - J. Vallerga Isoplanatic Angle (  0 ) & Sky Coverage Telescope Primary mirror h Bright stars +  0 = 1% sky coverage

IWORID 2004 Glasgow - J. Vallerga Can achieve >70% sky coverage with laser guide star adaptive optics!

IWORID 2004 Glasgow - J. Vallerga Laser Guide Star Parallax “Star” more of a streak Shape changes over pupil Can use pulsed laser to limit spatial extent Requires gated detector

IWORID 2004 Glasgow - J. Vallerga Deformable mirrors come in many sizes Range from 13 to > 900 actuators (degrees of freedom) Xinetics ~ 50 mm ~ 300mm

IWORID 2004 Glasgow - J. Vallerga 30 m telescope capability