Op#mal Es#ma#on of Starlight and Incoherent Light

Transcription

1 Op#mal Es#ma#on of Starlight and Incoherent Light A.J. Riggs, Tyler Groff, and Jeremy Kasdin Princeton University February 12, 2015 Work supported by the NASA Space Technology Research Fellowship 1

2 Overview: High Order Wavefront Sensing & Control Main Goal: Image faint exoplanets & disks. HOWFSC Methodology: a) Use DMs to provide diversity in focal plane. b) Es#mate focal plane E- field from intensity measurements. c) Calculate control signal and apply to DMs. d) Repeat (a)- (c) un#l desired contrast is reached. Main Points: 1) Use recursive es)ma)on for faster, more robust WFC. 2) Can also recursively es)mate incoherent light during WFC. 2

3 Recursive Wavefront Es#ma#on Observa#ons: Most of dark hole acquisi#on (wavefront correc#on) #me is spent ge\ng last order of magnitude in contrast. Measurements are dominated by readout noise. Op#mal recursive es#ma#on (Kalman filtering) u#lizes all measurements Reduces measurement noise and limits model uncertainty. Measured Contrast Less total #me is required for correc#on: 2 Pair Batch 2 Pair KF 1 Pair EKF Total Image Count References: Riggs et al., Demonstra#on of Symmetric Dark Holes Using Two Deformable Mirrors at the High- Contrast Imaging Testbed,SPIE, Groff & Kasdin, Kalman filtering techniques for focal plane electric field es#ma#on, JOSA- A, Princeton HCIL: Best Monochroma#c Results with Ripple3 SPC (Riggs, February 3, 2015) 3

4 Contrast Recursive WFE: Experimental Results Kalman filtering techniques for focal plane electric field es#ma#on 2 Pair Batch 1 Pair Kalman JPL HCIT: Best Monochroma#c Results with Ripple SPC (Riggs, August, 2013) In Riggs SPIE 88640T, Measured Contrast Total Image Count 2 Pair Batch 2 Pair KF 1 Pair EKF Total Image Count Princeton HCIL: Best Monochroma#c Results with Ripple3 SPC (Riggs, February 3, 2015) 4

5 Recursive Incoherent Light Es#ma#on Can also es#mate incoherent light recursively using a nonlinear es#mator. Currently trying extended Kalman filter (EKF). EKF just as fast (exposure & computa#onal #me) as KF, but also provides less noisy incoherent es#mate Reason for not using nonlinear es#mator: Correc#on might be done on other, brighter star What if there is zodi or exozodi? Need to es#mate incoherent light well and pre- subtract it from nominal PSF (or use just es#mated intensity of star) Helpful if any correc#on itera#ons required on science target star. 5

6 Incoherent Light Es#mates Recursive incoherent es#mate is less sensi#ve to measurement noise and shot noise. y(λ/d) 2 0 EKF: Starlight Estimate 6 7 y(λ/d) 2 0 KF: Starlight Estimate x(λ/d) x(λ/d) 8 y(λ/d) 2 0 EKF: Incoherent Estimate 6 7 y(λ/d) 2 0 KF: Incoherent Estimate x(λ/d) x(λ/d) 8 Data above are from the final itera#on of correc#on runs in Princeton s HCIL. KF and EKF data above are from separate correc#on runs In Princeton s HCIL, unclear if incoherent es#mate is stray light or something else. 1- sigma readout noise at 8e- 8 contrast (=5 ADU) 6

7 HOWFS Comparison Batch Process Kalman Filter (KF) Extended Kalman Filter (EKF) Pros Computa#onally fastest No tuning Less exposure #me Uses all probed images for recursive es#ma#on Allows for a dynamic model Less exposure #me Uses all images recursively Recursively es#mates incoherent light Allows for a dynamic model Allows for parameter adap#ve es#ma#on Cons More exposure #me Does not u#lize previous data Sta#c model only Computa#onally slower Must be well tuned Computa#onally slowest Must be very well tuned Less stable 7

8 Sensor Fusion: LOWFS & HOWFS Main ques#on: How best to combine LOWFS and HOWFS for a stable PSF? Key Points: LOWFS sampling much faster than HOWFS Will LOWFC residuals alter PSF above allowable contrast level? If yes: Major problem for scheme to calibrate on different star Must include in HOWFSC Possible solu#ons: 1) HOWFS can be blind to LOWFSC if LOWFSC residuals are negligible. 2) Include known LOWFC residuals and/or extra process noise in recursive HOWFS. 8

9 Extra Topics Best ways to speed up HOWFSC: Use broadband light. Obtain a beker system model. 1. Broadband HOWFSC Crucial for HOWFS to be fast enough. Currently, no alterna#ve to (monochroma#c) pairwise es#ma#on and EFC. Limited filter wheel space on AFTA 2. Model- based es#ma#on & control are very sensi#ve to accuracy of model How to use measurements to improve linear control response matrix? How to obtain DM registra#on and ini#al wavefront at DMs without phase retrieval on AFTA? 9

10 References EKF reference: Riggs et al., Op#mal Wavefront Es#ma#on of Incoherent Sources,SPIE, Kalman filter references: Groff & Kasdin, Kalman filtering techniques for focal plane electric field es#ma#on, JOSA- A, Riggs et al., Demonstra#on of Symmetric Dark Holes Using Two Deformable Mirrors at the High- Contrast Imaging Testbed,SPIE, Stroke minimiza#on: Pueyo et al., Op#mal dark hole genera#on via two deformable mirrors with stroke minimiza#on, Applied Op#cs, 2009 Groff & Kasdin, Kalman filtering techniques for focal plane electric field es#ma#on, JOSA- A, 2013 Pair- wise es#ma#on and EFC Give on et al., Pair- wise, deformable mirror, image plane- based diversity electric field es#ma#on for high contrast coronagraphy, SPIE,

11 Backup Slides 11

12 Princeton HCIL Layout Starlight Xpress SXV- M9 Diagram from [Groff JOSA- A 2013] Initial Image 3 Final Image 3 y(λ/d) WFC y(λ/d) x(λ/d) x(λ/d) 8 12

13 Measured Contrast Measured Contrast Es#mator Comparison: Princeton HCIL Results Batch 2 Pair KF 1 Pair KF 2 Pair EKF 1 Pair EKF Correction Iteration Batch 2 Pair KF 1 Pair KF 2 Pair EKF 1 Pair EKF Exposure #me is constant for all images. One- sigma measurement noise at 8e- 8 contrast. All recursive es#mators are faster than the batch process es#mator Total Image Count 13

14 Incoherent Light Es#mates In Princeton s HCIL, unclear if incoherent es#mate is readout noise or stray light. 1- sigma readout noise at 8e- 8 contrast (=5 ADU) 10 5 Incoherent Estimate Measured Contrast 10 6 Batch 2 Pair KF 1 Pair KF 2 Pair EKF 1 Pair EKF Total Image Count 14

15 Example Contrast Correc#on Curves Contrast Pair EKF Measured Estimated Incoherent Est. Meas. Avg. Probe Readout Std Dev Contrast Pair KF Iteration Measured Estimated Incoherent Est. Meas. Avg. Probe Readout Std Dev Princeton HCIL: 3 Feb Iteration 15

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