FLAO_01:FLAO system baseline & goal performance

F. Quirós-Pacheco, L. Busoni

FLAO system external review, Florence, 30/31 March 2009

FLAO system external review, Florence, 30/31 March 2009 2

O u t l i n e

• FLAO system simulator

• Optimized performance vs star magnitude

• Additional error sources

• Baseline & Goal performance @ Solar Tower

• Baseline & Goal performance @ Telescope

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FLAO system simulator

• Fourier optics code with tilt modulation.• CCD39 characteristics (RON, QE, c=750nm)• Sampling with different binning modes• WFS board transmission: 0.6

Binning

mode

Pupil size (subapertures)

1 30x30

2 15x15

3 10x10

4 7.5x7.5

Readout speed

(kpix/sec)

Average

RON

Worst

RON

Typical mode

of operation

2500 11.5 14.0 Bin1, fs 1000Hz

380 4.0 5.0 Bin2, fs 625Hz

335 3.5 5.0 Bin4, fs 200Hz

Total delay (tot)tot = 2T (for binning 1 and 2)tot = T (for binning 3 and 4)

11)(

z

gzC

• Influence functions from finite-element model.• Controlled modes: KLs fitted by the ASM.

Adaptive Secondary Mirror ( ASM )

Pyramid wavefront sensor ( PWFS )

Atmospheric Turbulence

• Two Von-Karman phase screens• No realistic profile (on-axis perf.)• Temporal evolution: Taylor

Telescope• Diameter: 8.22m• Central obscuration: 11%• Transmission: 0.93

Controller

• Simple Integrator:

• Kalman filter

Turbulence

Controller

ASM

PWFS

ASM

ControllerPWFSTurbulence

WFS noise

+++-

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Optimized Strehl vs. Magnitude

MR Binning mode

fs(Hz)

T (ms)

tot photons / subap. / frame

RON (e- rms)

nmod mod. (wfs/

D)

g %SR (H band)

7.5 1 1000 1.00 2T 535 11.5 630 2.0 0.9 84.6

8.5 1 1000 1.00 2T 213 11.5 595 2.0 0.8 83.2

9.5 1 1000 1.00 2T 85 11.5 496 2.0 0.7 79.5

10.5 1 600 1.67 2T 56 11.5 435 2.0 0.9 68.8

11.5 1 400 2.50 2T 34 7.0 378 3.0 0.9 57.3

11.5 2 625 1.60 2T 84 4.0 153 3.0 0.9 59.1

12.5 2 625 1.60 2T 34 4.0 153 3.0 0.8 53.5

13.5 2 550 1.82 2T 15 4.0 120 3.0 0.8 36.9

13.5 3 300 3.33 T 59 3.5 66 6.0 0.9 36.9

14.5 3 200 5.00 T 35 3.5 66 6.0 0.9 27.4

15.5 3 100 10.0 T 28 3.5 45 6.0 0.9 10.7

15.5 4 200 5.00 T 28 3.5 36 6.0 0.8 12.1

16.5 4 100 10.0 T 22 3.5 36 6.0 0.9 5.2

17.5 4 75 13.3 T 12 3.5 28 6.0 0.9 1.6

Turbulence: s=0.8”, L0=40m, V=15m/s

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Additional Error Sources

• Error budget has been estimated for these sources:– Pupil re-rotator: effect of jittering on scientific PSF– Effect of pupil displacement on the pyramid WFS– System calibration with double-pass optical setup: effect of thin

shell residuals– Effect of swing arm shadowing on the WFS– Effect of swing arm vibrations

• Additional error sources to be analyzed:– Effect of non-optimal clocking between actuators & subapertures– Effect of ASM capacitive sensors’ miscalibration– Effect of ASM actuator’s saturation– (?)

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Effect of Pupil Displacement

Error source Error budget (pixels)

Misalignment within WFS board (mostly from derotator)

0.1

Displacement of M2

(positioning error + flexures)

0.03

Displacement of M3

(positioning error + flexures)

0.03

Tilt of M3 (from diff. flexures) 0.08

Additional margin 0.15

Total (in quadrature) 0.2

Bin1, 671 modes, 2/D, shift = 0.2 pix

Integrator controller and tot = 2T : Absolute stability (no margins): 0 g 1 Relative stability (PM>45°, GM>3dB): 0 g 0.53 Other controllers?

Stability issues

Bin1, 671 modes, 2/D, shift = 0.2 pix

WFE ~ 1nm rms if g 0.5

FLAO system external review, Florence, 30/31 March 2009 7

At the telescope, Bin1, 671 modes, 2/D

Effect of Thin Shell Residuals

TS3 residuals(15.5 nm rms)

Sx

Sy

Slope-null vector

Stability constraints: g 0.7 WFE ~ TS residuals in single pass

• At the Telescope:– Double-pass setup:

• IM calibration• Slope-null acquisiton

– Single-pass setup:• On-sky operation

• At the Solar Tower:– Always double-pass

Double-pass optical setup

TS residuals specs.

Baseline Goal

60 nm rms 30 nm rms

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Effect of Telescope Vibrations

• The ASM swing arm has resonance frequencies from 15 to 30Hz.• Vibrations mainly cause an additional jitter (tip-tilt modes) of the image.• IRTC image analysis @ LBT: image jitter > 175 mas rms!!!

– Further vibrations’ characterization campaign and in-situ mitigation required at LBT.• Mitigation of remaining vibrations using hybrid controller Kalman filter for tip-

tilt, integrator for all other modes (G. Agapito, et. al., Proc of SPIE, Vol 7015, 2008)

Turbulence: s=0.8’’, L0=22m, V=20m/sPerformance loss due to residual jitter

(Sandler et. al., JOSAA 21, 1994):

Vibration causing a jitter of 80mas on tip-tilt modes at 20Hz

FLAO system external review, Florence, 30/31 March 2009 9

Baseline and Goal Performance @ Solar Tower

• Baseline performance– Worst measured RON– nmod < 351– Stability (bin1): g 0.5– Pupil disp.: 0.2pix– TS residuals:

• Optical setup:– Calibration in double pass– Operation in double pass

• TS baseline: 60 nm rms• Error budget:120 nm rms• SR (H band) loss factor: 0.81

– No vibrations considered

• Goal performance– Average measured RON– nmod: optimal value.– Stability (bin1): g 0.5– Pupil disp.: 0.2pix– TS residuals:

• Optical setup:– Calibration in double pass– Operation in double pass

• TS goal: 30 nm rms• Error budget: 60 nm rms• SR (H band) loss factor: 0.95

– No vibrations considered

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Baseline and Goal Performance @ the Telescope

• Baseline performance– Worst measured RON– nmod < 351– Stability (bin1): g 0.5– Pupil disp.: 0.2pix– TS residuals:

• Optical setup:– Calibration in double pass– Operation in single pass

• TS baseline: 60 nm rms• Error budget: 60 nm rms• SR (H band) loss factor: 0.95

– No vibration compensation• Conventional controller• Hybrid (Kalman) controller (?)

• Goal performance– Average measured RON– nmod: optimal value.– Stability (bin1): g 0.5– Pupil disp.: 0.2pix– TS residuals:

• Optical setup:– Calibration in double pass– Operation in single pass

• TS goal: 30 nm rms• Error budget: 30 nm rms• SR (H band) loss factor: 0.99

– Vibration compensation• Hybrid (Kalman) controller

Budget for residual jitter due to telescope vibrations needs to be defined.

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Questions?