GeMS Calibrations Schemes - obspm.frao4elt.lesia.obspm.fr/sites/ao4elt/IMG/pdf/Rigaut.pdf ·...
Transcript of 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 Garcia-Rissmann
Benoit Neichel
Damien Gratadour
Francois Rigaut
1Friday, June 26, 2009
AO4ELT, Paris, June 23-26 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
2Friday, June 26, 2009
AO4ELT, Paris, June 23-26 2009
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
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AO4ELT, Paris, June 23-26 2009
“Side” subsystems (infrastructure)Elevation platform extension
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AO4ELT, Paris, June 23-26 2009
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
6Friday, June 26, 2009
AO4ELT, Paris, June 23-26 2009
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
7Friday, June 26, 2009
AO4ELT, Paris, June 23-26 2009
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
7Friday, June 26, 2009
AO4ELT, Paris, June 23-26 2009
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
7Friday, June 26, 2009
AO4ELT, Paris, June 23-26 2009
Calibration sequences at a click...
Engineering/Calibration GUI
GTK + Python + Yorick based
Includes Real-timeDisplay 30fps
EPICS/socketcommunicationw/ RTC
9Friday, June 26, 2009
AO4ELT, Paris, June 23-26 2009
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
12Friday, June 26, 2009
AO4ELT, Paris, June 23-26 2009
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 |cg> |mg>
12Friday, June 26, 2009
AO4ELT, Paris, June 23-26 2009
Hadamard vs Synthetic IMAT
Hadamard Synthetic (YAO)
13Friday, June 26, 2009
AO4ELT, Paris, June 23-26 2009
Synthetic Matrices and how we use them
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
14Friday, June 26, 2009
AO4ELT, Paris, June 23-26 2009
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
#
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AO4ELT, Paris, June 23-26 2009
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
16Friday, June 26, 2009
AO4ELT, Paris, June 23-26 2009
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%
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AO4ELT, Paris, June 23-26 2009
Temporal performance: TT Xfer functions
800Hz sampling
Effect of quadcell(non-linearity)
200Hz sampling
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AO4ELT, Paris, June 23-26 2009
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)
19Friday, June 26, 2009
AO4ELT, Paris, June 23-26 2009
NGS centroid gains and loop gains optim
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
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NGS centroid gains and loop gains optim
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
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AO4ELT, Paris, June 23-26 2009
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...
22Friday, June 26, 2009
AO4ELT, Paris, June 23-26 2009
Tomography of static aberrations
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)
25Friday, June 26, 2009
AO4ELT, Paris, June 23-26 2009
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 !
27Friday, June 26, 2009