1 On-sky validation of LIFT on GeMS C. Plantet 1, S. Meimon 1, J.-M. Conan 1, B. Neichel 2, T. Fusco 1 1: ONERA, the French Aerospace Lab, Chatillon, France 2: Gemini Southern Observatory, La Serena, Chile Strong collaboration with B. Neichel from Gemini South

2 Outline I.Context and description of LIFT II.Validation at Gemini South III.Extension to the ELT context

3 Context Laser assisted AO: need to sense low order modes (tip/tilt/focus) on faint natural stars Classical solution: Shack- Hartmann 2x2  noise and aliasing issues  Find a NGS-WFS solution to increase sky coverage Goal: 1 to 2 magnitude gain Sodium layer Laser guide star Turbulent layer Laser Telescope

LIFT : LInearized Focal-plane Technique Maximum Likelihood estimation Focus = 0 Focus < 0 Focus > 0 LIFT: noise effective low order WFS  Optimized SNR Full aperture diffraction-limited focal-plane sensor Astigmatism offset: removes the focus sign ambiguity Linearization  Direct LO linear estimation (≡ WCoG)  Fast  Simple, fast, full aperture gain Simple! [Meimon10, Opt. Lett.]

5 Noise propagation comparison with the SH 2x2 and the pyramid Comparison of noise sensitivity for the estimation of tip/tilt and focus: Coefficient SH 2x2 (WCoG) LIFTPyramid Photon noise (α) Read-out noise (β) [Plantet13, Opt. Exp. (accepted)] Variance of estimation error in a WFS : Pyramid model: no modulation, pupil sampled on 4 pixels, ML estimation  Much more sensitive than a SH 2x2  Performance comparable to the pyramid  SH and pyramid proven efficient, let’s do it with LIFT!

6 Laboratory validation Linearity of estimation for tip/tilt and focus Estimation in large spectral bandwidth (R=3.4) Noise propagation confirmed [Plantet12, SPIE], [Plantet13, Opt. Exp. (accepted)] Source Tilted glass plate for astigmatism Camera Collimation and refocusing

LIFT features 7 Fast and efficient algorithm Much less sensitive to noise than a SH 2x2, comparable to a pyramid Easy to setup, move, debug Validated in lab  Let’s see on the sky!

Validation at Gemini South

What do we do? 9 Goal: Prove linearity of estimation on a star  retrieve same graph as in simulations:

10 Optical system: Canopus DMs TTM Toward IR science camera Calibration Sources LGSWFS NGSWFS Telescope light GSAOI [Bec08, SPIE] gemini.edu

11 Data acquisition Z4 offsets on ref slopes 3 Input Output rad Z5 offset 4 1 Close AO loop GSAOI: 2x2 Rockwell HAWAII-2RG 2048 x 2048 Fast On Detector Guide Window to select star [McGregor04, SPIE] LIFT

12 History 04/09/12: Linearity test on calibration sources  OK [Plantet12, SPIE]

13 Weather problems 3 nights window… 04/26 04/27 04/28

14 History 04/09/12: Linearity test on calibration sources  OK 04/26/12, 04/27/12 and 05/28/12: bad weather 04/27/12: Focus estimation on calibration sources with simulated residual turbulence  reproductible estimation End of 2012  new runs beginning 2 data sets: On sky data! But low Strehl ratio Data with SR ~ validation is possible! [Plantet12, SPIE]

15 Validation of linearity on sky Linearity and robustness confirmed! Data Model

Perspectives 16 More complete tests to come Close NGS loop with LIFT? Measurement of more low frequency: LIFT as a truth sensor (cut Mickey Mouse ears?) We performed LIFT on an operational system. How would it be on an ELT?

Extension to the ELT context

LIFT for LTAO: efficient low order WFS 18 Simple solution for a natural guide star WFS Dedicated DM + camera Benefits from full aperture gain Easy to setup, move, use, debug Very reliable Feature of ATLAS baseline [Fusco10, SPIE]

19 LIFT for MCAO: use of scientific detector MCAO systems  wide field of view  chances of having a natural star A region of interest can easily be extracted from the image  Add an astigmatism 10% (typically) of the time, and use LIFT on an image taken from the detector  Slow correction of focus and low order modes from all possible origins (sodium layer, internal errors…) Astigmatism respects the symmetry of the PSF < 1% loss in Strehl Ratio, unnoticeable on long exposure image

20 Conclusion First validation on sky! Seductive perspectives for ELTs To come : further comparison with other sensors, study of aliasing, tests for implementation in laser assisted systems Poster: SH + LIFT by Serge Meimon

21 Thank you!