Detectors for AO Wavefront Sensing Mark Downing G

Detectors for AO Wavefront Sensing Mark Downing, G. Finger, D. Baade, N. Hubin, J. Kolb, O. Iwert Instrumentation Division ESO Examine AO WFS Detector roadmap CCD 50 CCD 39 Advanced Developments / Tests at ESO Future Developments GMT, E-ELT, TMT CCD 60 Past Detectors CCD 220 pn. CCD MIT/LL MPI/HLL CCID-26/128 CCID-35 14/10/2009 Df. A 2009: AO WFS Detectors 1

Adaptive Optics (AO) - removing the twinkle of the stars Deformable mirror compensates the distorted wavefront, achieving diffraction-limited resolution 1 4 Wavefronts from astronomical objects are distorted by the Earth’s atmosphere, reducing the spatial resolution of large telescopes to that of a 10 cm telescope OFF 3 Control System computes commands for the deformable mirror(s) 14/10/2009 2 Wavefront Sensor measures deviation of wavefront from a flat (undistorted) wave Df. A 2009: AO WFS Detectors ON 2

Challenge = Speed vs Noise Biggest challenge for AO WFS detectors is the trade between: low noise (RON and dark current/count), and fast frame rates – becomes more difficult as format sizes increase – and finally power dissipation limits feasibility It is instructive to review how this trade has been achieved in the past. 14/10/2009 Df. A 2009: AO WFS Detectors 3

Add more outputs Achieves lower read noise at fast frame rates by reading through multiple outputs. Read noise of output amplifier e or iers M lif p m a Manufacturer Device 5 -10 e- CCD 50 Pixel Format Frame size (pixels) Rate 100 k 1 M 24μm 128 x 128 Rate pix/sec 1000 fps Amplifier Pixel CCD 39 24μm 80 x 80 1000 fps 4 10 e- ~ 90% CCID-26/64 21μm 64 x 64 600 fps 4 6 -7 e- ~ 90% CCID-26/12 21μm 128 x 128 1000 fps 16 5 e- ~ 90% 10 k Outputs RON ( rms) QE 16 5 ee 2 v ~ 90% 10 M E 2 v MIT/LL 14/10/2009 Df. A 2009: AO WFS Detectors 4

Improve the amplifier design Achieves lower read noise by designing better amplifiers. • Type of amplifier (JFET or MOSFET, “p” or “n”). • RON Geometry (Wx. L) of amplifier. • Oxide thickness. • Reduce capacitances (floating diffusion and parasitic). → The higher the conversion gain the lower is the noise. Improve amplifier MIT/LL • Barry Burke (MIT/LL) CCID-56 160 x 160 21 µm pixel 20 outputs: New p. JFET amplifier design 100 k 1 M – Reporting ~ 2. 5 e-Amplifier Pixel (800 fps) at 1 Mpix/sec Rate pix/sec – • 10 M 256 x 256 by 21 µm pixel, 32/64 outputs in development e 2 v Refer back to talk by Vyshnavi Suntharalingam, “Advanced Imager Technology Development at MIT Lincoln Laboratory” 14/10/2009 Df. A 2009: AO WFS Detectors 5

Add EMCCD gain in the serial register Achieves lower read noise by adding electron multiplication register before the amplifier. If 1 If 2 If 3 Electron E 2 v L 3 Vision: Multiplication << 1 e- RON at output amplifier speeds of 16 Mpix/sec Register • CCD 60 128 x 128 24 µm pixel. 1, 000 fps with 1 output. • CCD 220 240 x 240 24 µm pixel. Rf 1 Rf 2 Rf 3 1, 200 fps with 8 outputs. Rf 2 HV 14/10/2009 Df. A 2009: AO WFS Detectors 6

Customize the architecture Achieves lower read noise by minimizing the number of pixels read out by custom designing the architecture to the application. Polar Co-ordinate CCD - talk about later Curvature CCD, CCID-35 – R. Dorn (ESO), J. Beletic, and B. Burke (MIT/LL). – 8 x 10 subapertues, – RON < 1. 2 e- at 4 kfps and QE > 80%, – Successfully used in upgrade to Fly. Eyes at CFHT. See poster Kevin Ho, “Flyeyes: Upgrade of CFHT’s AO System Using an MIT-LL CCID 35 Sensor” Array design Sub-aperture design Image Area – 20 x 20 18µm pixels Storage Area #2 14/10/2009 Buffer Storage Area #1 Serial register MIT/LL Df. A 2009: AO WFS Detectors 7

Add gain in the pixel => APD Achieves lower read noise by Electron Multiplication Gain in the pixel. • • Build detector from array of single APDs or better an APD array. Downside is silicon APDs have statistical variation of gain that results in an excess noise factor of ~ 2 -3 Overcome by operating the APD in high gain “Geiger” mode to discriminate and count single photon events and thus essentially offer zero read noise. • e. g. Poli. MI SPADA (Single Photon Avalanche Diode Arrays) p 80 APDs QE ~ 40% dark count rates < 3000 counts/sec/pixel Photon counter → zero read noise at 20 kfps n e h p+ substrate SPADA 14/10/2009 Df. A 2009: AO WFS Detectors 8

Detectors for AO wavefront sensing Mark Downing, G. Finger, D. Baade, N. Hubin, J. Kolb, O. Iwert ODT / Instrumentation Division ESO FUNDING: OPTICON FP 6 -WFS SH 40 x 40 sub-ap. 6 x 6 pixels/sub-ap. 240 x 240 pixels VLT Instruments SPHERE, AOF – MUSE and HAWK-I Future Developments GMT, E-ELT, TMT Detectors in Advanced Development/ Test at ESO Past Detectors E 2 v CCD 220 14/10/2009 MPI/HLL pn. CCD Df. A 2009: AO WFS Detectors 9

e 2 v CCD 220 FP 6 OP 4 Gain Registers OP 3 OP 2 Gain Registers Image Area Metal Buttressed 2Φ 10 Mhz Clocks for fast image to store transfer rates. Image Area Store Area 240 x 120 24□µm Gain Registers Store Area 8 L 3 Vision Gain Registers/Outputs Each 15 Mpix. /s. OP 8 OP 7 Gain Registers OP 1 OP 6 OP 5 e 2 v CCD 220: Split frame transfer CCD 240 x 240 24 µm pixels 8 L 3 Vision EMCCD outputs << 1 e- RON at 1, 200 fps Next talk Philippe Feautrier “OCam and CCD 220 - World's Fastest and Most Sensitive Astronomical Camera” 14/10/2009 Df. A 2009: AO WFS Detectors 10

CCD 220 Status Several Test Cameras in operation Devices in house that meet specs. → built by LAM, LAOG, OHP y log d no ch ferre e s T n tra ü ESO’s NGC WFS Camera Head is at advanced stage of prototype Reported in Javier REYES poster “ESO AO Wavefront Sensor Camera” 14/10/2009 Df. A 2009: AO WFS Detectors 11

MPI/HLL pn. CCD (Robert Hartmann, Sebastian Ihle, Heike Soltau, Lothar Strueder) CAMEX 1 CAMEX 2 • Max Planck Institut /Halbleiterlabor • pn. CCD 256 x 256 pixels 51 um pitch • 450 um thick fully depleted excellent red response & no fringing 300 V backside bias for good PSF • Target: RON < 3 e- at 1000 fps • Split frame transfer • Fast readout → Column Parallel CCD one output amplifier per column • Total of 528 amplifiers but CAMEX (mux 132 to 1) for easy I/F CAMEX 3 CAMEX 4 Only 8 analog output nodes MPI/HLL 14/10/2009 Df. A 2009: AO WFS Detectors 12

pn. CCD: Testing at ESO funded by OPTICON FP 6 → Excellent QE, PSF, and low read noise Spot scanning used to measure PSF FP 6 • QE pn. CCD • Charge in Central Line (%) • % of charge in central line of pn. CCD versus scan position. • QE % • 100 • 90 • 80 • 70 • 60 • 50 • 40 • 30 • 20 • 10 • 300 • 400 • 500 • 600 • 700 • 800 • 900 • 1000 • 1100 51µm Pixel • 100 • 80 • 60 • 40 • λ=400 nm Vss=200 V • 20 • λ=700 nm Vss=250 V • 0 • -50 • -40 • -30 • -20 • -10 • 0 • Wavelength [nm] • 10 • 20 • 30 • 40 • 50 • Position (µm) QE: Excellent QE into the “Red” → good for Natural Guide Star applications. 450 µm thick silicon is able to collect the deep penetrating red photons. PSF: Measured < 0. 45 pixel over 400 -900 nm (exceeds specs of < 0. 8 pixel). Pixels could be halved in size and still meet requirements. RON: < 2. 5 e-rms. 14/10/2009 Df. A 2009: AO WFS Detectors 13

Development to add APD output → AApn. CCD (Avalanche Amplified pn. CCD) Part Funded by ESO and OPTICON FP 6 Paper Lothar Strüder MPE/HLL “Single Photon Counting in the Optical” Add avalanche stage before output amplifier 14/10/2009 MPI/HLL Df. A 2009: AO WFS Detectors 14

Detectors for AO wavefront sensing Mark Downing, G. Finger, D. Baade, N. Hubin, J. Kolb, O. Iwert ODT / Instrumentation Division ESO AO WFS roadmap Future Developments GMT, E-ELT, TMT Detector in Advanced Development/ Test at ESO • Detectors required? • Top Level Requirements • Possible technologies Past Detectors 14/10/2009 Df. A 2009: AO WFS Detectors 15

AO Detector needs for ELTs Low Order AO Pyramid Tip. Tilt Sensors NGS Ground Layer. A O Shack Hartmann Quad -Cell LGS Multi Conjugate AO Other WFS… Guiding 14/10/2009 Laser Tomography AO LGS Ground Layer AO Multi. Object AO Large visible fast low-noise detector for Shack-Hartmann based AO WFS Existing visible high performance detector (i. e. CCD 220) Extreme AO NGS Single Conjugate AO 3 k. Hz ultra lownoise detector IR WFS IR Tip. Tilt sensors Df. A 2009: AO WFS Detectors IR detectors development 16

Large Visible AO WFS Detector needed to sample the spot elongation Sodium T ~ 10 km layer H ~ 80 km Sodium Laser Guide Stars (589 nm) • AO systems operate at ~1 k. Hz frame rate • Bright “guide stars” are required • Only 1% of the sky is accessible with natural guide stars • Sodium layer at 80 -90 km altitude can be stimulated to produce artificial guide stars anywhere on the sky • Pulsed laser can be used to range gate to limit laser spot elongation Predicted spot elongation pattern LLT Pupil plane Detector plane Distance from launch site 14/10/2009 Df. A 2009: AO WFS Detectors 17

Large Visible AO WFS Detector Top Level Requirements (developed from very detailed simulations) Parameter Specification Array Format 1680 x 1680 pixels Pixel Size 24 -50 µm 460 -950 nm (NGS) 589 nm (LGS) 700 fps < 3 e- rms > 80 % < 0. 5 e-/s/pixel < 4000 e-/pixel < 1. 5%. Wavelength Frame Rate RON QE Dark Current Storage Capacity Cosmetics Comment 84 x 84 sub-apert. each with 20 x 20 pixels to sample the spot elongation Large Fast Low noise High Low Expect few photons Good; very few bad sub-apertures • Ease of use/compact size: integral Peltier digital I/F preferred 14/10/2009 Df. A 2009: AO WFS Detectors 18

Large Visible AO WFS Detector Plan (Multi-Phase Development) 2007 Design Study Technology Validation Technology Demonstrator Scaled-down Demonstrator Development Testing/ Acceptance 2008 2009 2010 2011 2012 2014 2015 Several Design Studies Retire Investigated many different technologies Retire Pixel Risks Most promising –Architecture/ CMOS Imager, APD array TD Process Risks and orthogonal EMCCD SDD Full size device meeting all specs. Several Technology Demonstrators. Scale Full Engineering exercise All CMOS Imagers - most Demonstrator likely to succeed retire pixel risk by demonstration noise x Authorize speed with good imaging capability (no image lag) Testing Production Scaled Down Demonstrator architectural risks by fab. ~ ¼ imager Highly likely CMOS Usable device on Telescope Production Phase Retire 14/10/2009 2013 Df. A 2009: AO WFS Detectors Production 30 Science Devices 19

With recent improvements CMOS now rival CCDs 1. Pinned Photo Diode → low dark current (10 p. A/cm 2) supply voltage 0. 5 e-/pix/frame with modest cooling (-10 Deg. C) 2. reset High conversion gains (200 µV/e-) → low RON of < 2 e- transfer gate - by reducing sense node capacitance < 0. 8 f. F 3. Buried channel MOSFETs → reduces/eliminates RTS signal noise 4. 1 4 3 Build from thicker high resistivity silicon and ‘substrate biasing’ FD PPD column output low crosstalk and good response 5. Multi-sample the pixel at different conversion gains (µV/e-) improves dynamic range and linearity PLUS the long offered advantages of 4. Fast frame rates → highly parallel readout: ultimate of amplifier pixel. 5. Low power → µA instead of m. A (CCD) transistor bias currents. 6. Monolithic integration of support circuitry; biases, sequencer, clocks, ADCs… Offers a simple, easy-to-use digital interface. 14/10/2009 Df. A 2009: AO WFS Detectors Read 2 20

Polar Co-ordinate CCD Customizes CCD architecture to: minimize no. of pixels to be read out reduce image to store transfer time conceived by Jim Beletic, Sean Akins of KECK; Barry Burke (MIT/LL) being developed by Sean Akins, Brian Aull, Brad Felton (MIT/LL) - - Storage Area Imaging Area and Robert Reich) Image Clocks Read out fewer pixels 14/10/2009 Serial Register Df. A 2009: AO WFS Detectors Storage Clocks 21

Pulsed laser: track spot on CCD Spot contained in much smaller number of pixels and only these need to be read out Na Layer Typical pixel array § CCD needs to be customized: Clock annulus – for each new application, or – application configured or restricted to use existing CCD; e. g. use center projected laser and < 60 x 60 sub-apertures. § Scalability: Pulsed – Laser May not be Clock CCD charge with scalable to 120 x 120 the spot sub-apertures Laser projection Typical subaperture point 512 amplifiers could be challenging. and move charge back and forth to collect photons from several pulses before reading out. 14/10/2009 Df. A 2009: AO WFS Detectors 10 annuli clocked separately to optimally track spot 22

IR AO WFS Detectors Requirements • RON has limited use to low order Tip/Tilt and “Truth” sensors – Scientific detectors used: HAWAII-XRG (10 e-) and the PICNIC (20 e-) – • Talk David Hale “Low-noise IR Wavefront Sensing with a Teledyne Hx. RG” For E-ELT much better detectors are needed: – e-APD – Teledyne Speedster Parameter Array Format Specification Minimum Goal 256 x 256 pixels Pixel Size 18 -40 µm Wavelength 0. 8 -2. 5 µm Frame Rate 750 fps 1500 fps < 5 e- rms 3 e- rms > 70 % > 80 % < 3 e-/s/pixel < 1 e-/s/pixel 10 k 20 k RON QE Dark Current Storage Capacity (e-/pix) 14/10/2009 Df. A 2009: AO WFS Detectors 40 µm 23

e-APDs • APDs in linear mode have excess noise factor, F > 1 – Typically 2 -3 for silicon and 3 -5 for III-V materials • In Hg. Cd. Te: F ~ 1 in linear mode has been demonstrated – E. g. LETI: gain of 5300 and F ~ 1. 05 -1. 3 at reverse bias of 12. 5 V. – impact ionization occurs mostly by single carrier, electrons, rather than the larger, slower, and less deterministic holes. • ESO has funded SELEX to develop a 24 µm 320 x 256 prototype detector: – λc = 2. 5 µm – Prototype operational and initial results are encouraging. Several developments: see session on APDs on Thursday afternoon Ian BAKER (SELEX), “Hg. Cd. Te Avalanche Photodiode Arrays for Wavefront Sensing and Interferometry Applications”. Don Hall (If. A and Teledyne), “Electron-Avalanche and Hole-Avalanche Hg. Cd. Te Photodiode Arrays for Astronomy” Johan Rothman (CEA Leti-Minatec), “APD Development at CEA Leti-Minatec” 14/10/2009 Df. A 2009: AO WFS Detectors 24

Teledyne Speedster • Speedster 128 (designed 2005) • • 128 x 128 pixels 40 µm pixel pitch Digital input – clocks and biases generated on-chip Analog output Two gain settings – high gain for lowest noise Chip functionality and performance (in low gain) proven High gain mode (which should be lowest noise) does not work as designed Speedster 256 -D (designed 2008) • • • fix of Speedster 128 design Improved CTIA pixel 256 x 256 pixels 12 bit analog-to-digital converters on-board Up to 10 k. Hz frame rate Refer back to Jim Beletic’s talk “Teledyne Imaging Sensors - Producer of detectors with a dynamic range of 1 million. . in several dimensions” 14/10/2009 27/6/2008 Df. ADetectors for AODetectors 2009: AO WFS 25

Conclusion • Current detector developments at ESO are on track to meet current instrument needs. • Innovative detector developments are required for the ELTs. • ESO is actively involved with Detector Manufacturers to lay the foundations to meet these needs. 14/10/2009 Df. A 2009: AO WFS Detectors 26

THANK YOU 14/10/2009 Df. A 2009: AO WFS Detectors 27