GeMS Calibrations Schemes - obspm.frao4elt.lesia.obspm.fr/sites/ao4elt/IMG/pdf/Rigaut.pdf · AO4ELT, Paris, June 23-26 2009 GeMS Calibrations Schemes Matthieu Bec Maxime Boccas Aurea

AO4ELT, Paris, June 23-26 2009

GeMS Calibrations Schemes

Matthieu Bec Maxime Boccas

Aurea Garcia-Rissmann

Benoit Neichel

Damien Gratadour

Francois Rigaut

1Friday, June 26, 2009


Talk outline

GeMS intro

Diagnostics, facilities, documentation

Calibrations issues and techniquesWhat works and what doesn’t...

Synthetic matrices and how/why we use it

LGS centroid gains tracking

DMs/LGS WFSs registration

Temporal perfomance

NGS loop gain optimization and centroid gains tracking

Tomography of static aberrations (w/ GSAOI input)

Summary and hard numbers



CA

NO

PU

S

}GeMS in numbers

5 LGS WFS 16x16 Shack-Hartmann

3 Deformable Mirrors totaling ~800 actuators, conjugated to 0, 4.5 and 9km ranges

3 APD based NGS Tip-Tilt WFS

1 NGS slow focus WFS

1 x 50W laser divided in 5 x 10W beams placed on the corners and center of a 1' FoV

2 dedicated instruments:GSAOI (4k2 NIR imager), 80” FoV (20mas pixels) !

Flamingo II (NIR MOS), 2' FoV

Many subsystems: ASCAM, Safety systems, infrastructure, laser(s), BTO, LLT, etc...

3



“Side” subsystems (infrastructure)Elevation platform extension



Laser Infrastructure (LSE)



GeMS Status

Laser:Keck laser going through AT as we speak (delivers 40W, 20W spec)

but, LMCT short in resources to finish laser (fuzzy)

Planned delivery date: August 2009

CANOPUS:Going through I&T in the Gemini SBF lab

No major performance issue to date

Big software integration/automation/optimization effort

Remaining issues: Cooling redesign, electronic integration, TTWFS throughput

Other subsystems (BTO/LLT/Infrastructure/Safety) proceeding well

First light 2010A



Blog:339 Blog posts

1 post every 1.5 days

twikiLots of twiki pages

Updated regularly

Many of the team are using it

Documentation, Blog



Blog:339 Blog posts



Updated regularly


Documentation, Blog



Blog:339 Blog posts



Updated regularly


Documentation, Blog



GeMS components, loops & offloads



Calibration sequences at a click...

Engineering/Calibration GUI

GTK + Python + Yorick based

Includes Real-timeDisplay 30fps

EPICS/socketcommunicationw/ RTC






Shiny Instrument Status Display



Synthetic Matrices and how we use them

Experimental IMAT supposed to take every linear effect into account:

actuator gains

actuator influence functions

WFS subaperture gain

global and local misregistration

others???

Only static and linear effects included

Experimental IMAT limited by noise

In LGS MCAO/LTAO/MOAO systems, IMAT = f (elevation)

Can we use synthetic IMATs?

Actuator influence function adjusted using exp. IMAT

Misregistration under controlled (calib. for flexure, LUTs)

|c> = |m> E




Experimental IMAT supposed to take every linear effect into account:

actuator gains

actuator influence functions

WFS subaperture gain

global and local misregistration

others???

Only static and linear effects included

Experimental IMAT limited by noise

In LGS MCAO/LTAO/MOAO systems, IMAT = f (elevation)

Can we use synthetic IMATs?

Actuator influence function adjusted using exp. IMAT

Misregistration under controlled (calib. for flexure, LUTs)

|c> = |m> E |cg> |mg>



Hadamard vs Synthetic IMAT

Hadamard Synthetic (YAO)




loop stable up to highest theoretical loop gains

CILAS DMs stable (Inf.Funct. and gain, gain=1)

Independant on-line tracking of LGS cent.gains

LUT for DM/LGS registration

Using synthetic matrices minimizes noise propagation

Bonus: Having a good model of the system allows a more fidel use of simulation tools to check system performance

Non-linearity: same issues for exp. IMAT



LGS centroid gains (CG) on sky: Dithering

Principle:Dither LGS

using dithering TT platform @ laser launch

baseline 50mas radius (negligible impact on linearity)

Lock in detection on each subaperture

CG correction factor = ( induced (50mas) / measured ) "

CGs modeled and constrained toConstant (over subapertures) over X

Constant over Y

Radial elongation

Static part

}# Spot elongation /Na layer thickness

# Lenslets / local aberrations

seeinglaser beam qualityoptical aberrations @ launch

#



LGS centroid gains on sky: DitheringImplemented in Altair, works (NCPA const. over months)

Requirements:Accurate calibration of dithering platform amplitude

Good knowledge of system loop transfer functions

Watch out for vibration contribution

In the lab: swipe spot within quadcell using Tip-Tilt

Jerry Nelson’s original idea (published by Gratadour/Rigaut)

by-product: Na Layer thickness



DMs / LGS WFSs registration

2 methods:! Quick: on-line:

1. Push on 8 external DM actuators, visible by all WFSs

2. Compute actual position w.r.t. expected position

3. Deduce X/Y misregistration, magnification, rotation

" Full: off-line, not automated (yet): 1. Record experimental Hadamard IMAT

2. For each line, generate synthetic measurement set

3. Minimize distance by varying xy positions of synthetic actuator

4. # Full map of pupil distortion (DM to lenslets)

DM0 / WFS0 Registration/distortion

rms misregistration < 3%



Temporal performance: TT Xfer functions

800Hz sampling

Effect of quadcell(non-linearity)

200Hz sampling



NGS centroid gains and loop gains optim

GeMS designed before dithering method was known/mature

No integrated dither mechanism in NGS WFS

Impossible to use TT without impacting the science image (although this is what we do in altair)

Initial plans were to use LUT for CG = f (seeing)

It is however important to have a good knowledge of CGs for:

NCPA (plate scale, global image motion)

Mode gain optimization (you need a good knowledge of system transfer functions, hence of system loop gain, hence of CG)




New method developed. Use of a temporal property to measure a spatial parameter

Makes use of the prior that noise is white -> Open loop PSD of signal should be flat from [~100,400] Hz

Open loop PSD is retrieved from close loop / rejection xfer function

Assuming a simple integrator, loop gain and centroid gains are 2 scalar, merged and factored-in to slopes

Try family of gain, find one that satisfy flatness of high frequency -> found error on gain, thus centroid gains.

In one shot, centroid gains are re-adjusted and loop gains is optimized



Limitation: does not work

when loop gain is too low

(no overshoot)

fix: work at lower sampling rate

& larger loop gain

Right: example with varying

noise level, with or without

atmospheric Tip-Tilt, with

or without high order

atmospheric component.

CGs (Tip & Tilt)

Optimized TT loop gains

Time [s]

Valu

e



Tomography of static aberrations

Using a 20x20 SH WFS in the output focal plane

Record one position at a time (steerable)

Problem is to find WFS offset slopes that induce a DM static shape that minimize the phase error in output focal plane

When optimizing in a single arbitrary location, H band Strehl are improved from [5%-70%] # 99% in one iteration (80 first DWFS Z). This means we understand:

linearity and calibration of output focal plane SHWFS

linearity and calibration of LGS WFSs

IMAT and CMAT (normalization, etc...)

When doing a global optimization in the whole field of view (9 points), the problem is more complex...










In simulation, we can get H band Strehl of 97% over the 9 points, by filtering less spatial modes

On the bench, we get approximately (H band Strehl)95% at the edge

85% in inner locations

78% at very center

Still not completely understood. We believe this comes from local aberrations in optical elements way off from the domain which is correctable by DMs (0-9km)

A more complete tomographic reconstruction including the suspected optical surfaces still to be done

GSAOI: curvature images + diversity @ 4x4 locations + MAP reconstruction (stability + sensitivity)



All loops closed in the lab

26



Summary and hard numbers

CCD noise 3.5e- regularly

Vibrations measured on LGS WFSs = 1-2milliarcsec

Static output H Strehl as measured by our 20x20DWFS, after application of NCPAs:

99% when optimized in an arbitrary single direction

80-96% when optimized over entire FoV

0dD error/rejection bandwidth = 55Hz approx

NGS loop gain + centroid gain global optimization working

dithering/LGS centroid gains working (FWHM~1.4arcsec, PED issue)

Aurea is looking for a job !


Documents

GeMS Calibrations Schemes - obspm.frao4elt.lesia.obspm.fr/sites/ao4elt/IMG/pdf/Rigaut.pdf · AO4ELT, Paris, June 23-26 2009 GeMS Calibrations Schemes Matthieu Bec Maxime Boccas Aurea