lgs spot truncation mitigation in elt wide field …...lgs spot truncation mitigation in elt wide...

LGS spot truncation mitigation in ELT Wide Field Adaptive Optics

L.Blanco1, C. Correia1, T. Fusco2, B. Neichel1, Y. Ono1, K. El Hadi1

1 Laboratoire d’Astrophysique de Marseille (UMR7326 - CNRS-INSU, Université d’Aix-Marseille) 2 ONERA - The French Aerospace Lab

LGS Spot elongation

LLT

Sodium layer

D e t e c t o r plane

T ~ 20km

H ~ 90km

Distance from launch site

P u p i l plane

Predicted spot elongation pattern

LLT

2WFS Workshop, Padova 2017

3

LLT


P u p i l plane

25”

1”

Ideally, we need subapertures with 25x25 pixels of ~1”

For 80x80 subapertures, we need 2000 x 2000 pixels

Most likely, we will have no more than 10x10 pixels

On a ~40m telescope

LGS Spot elongation

Strong truncation

WFS Workshop, Padova 2017

Elongated spots cropping

What if we completely discarded the biased measurements from the subapertures with the most truncated spots ?



Spot elongation∝distance from laser launch telescope DLLT ->we ‘crop’ the subapertures at DLLT > D x (1-pupcrop)

Highly truncatedPartially truncated

Not truncated

pupcrop=0

5





Not truncated

Highly truncatedPartially truncated

pupcrop=25%

6





Not truncated

Partially truncatedHighly truncated

pupcrop=50%

Killer for 1 WFS…

7



8



pupcrop=10%

pupcrop=30%

WFS1 WFS2 WFS3 WFS4

But we have redundancy

8



9

LLT


P u p i l plane

25”

1”

On a ~40m telescope

Full E-ELT simulation: Pupil diameter : 37m

74x74 SH LGS WFS 75x75 actuator DM (Fried

geometry) Subaperture pitch : 50cm

Subaperture FOV : 10’’ (1’’ pixels) 6 LGS-Asterism diameter : 42’’

30% central obscuration

E2E simulations (OOMAO)



74x74 SH LGS WFS 75x75 actuator DM

Subaperture pitch : 50cm Subaperture FOV : 10’’ (1’’ pixels)

6 LGS-Asterism diameter : 42’’ 30% central obscuration

High flux







High flux







High flux

Performance increases as we discard subapertures with too large an elongation/truncation

WFE due to elongation reduced from 152nm to 106nm RMS


223nm

270nm247nm

18

152nm106nm


Differential subaperture weighting

- à la Tallon 2008/Robert 2010 - Takes into account the elongation in the noise covariance matrix - Takes into account cross-coupling between X and Y slopes


223nm

Subaperture weighting+cropping





High flux

270nm247nm

WFE due to elongation reduced from 152nm to 83nm RMS when using subaperture differential weighting

but Na profile not always bimodal !

238nm

Stre

hl in

K-b

and

(%)


SODIUM DENSITY PROFILE VARIATIONS

21Pfrommer and Hickson 2011

13.7% 18.6% 16.7%

15.8% 15.3% 11.2%

8.7%



226nm

234nm

223nm






High flux

Narrow spot mostly within the subaperture even opposite from LLT

Weighting over-regularizes already good information

Stre

hl in

K-b

and

(%)


223nm

270nm

238nm247nm






High flux


Stre

hl in

K-b

and

(%)


223nm

275nm

226nm

257nm






High flux

Differential weighting gives almost ideal performance

Stre

hl in

K-b

and

(%)


223nm

265nm

237nm247nm






High flux


Best ‘cropping’ (20%) WFE due to elongation =106nm

Stre

hl in

K-b

and

(%)


223nm

335nm

238nm 250nm233nm






High flux


WFE reduced to 67nm RMS when combining weighting and cropping

Stre

hl in

K-b

and

(%)


223nm

349nm

318nm330nm






High flux

Very perturbed profile with sharp peak at high altitude Unstable loop when taking into account all subapertures Weighting mandatory for full pupil High cropping (40%) improves performance over weighting but far from ideal

Stre

hl in

K-b

and

(%)


223nm

400nm

300nm

337nm






High flux

Stre

hl in

K-b

and

(%)

Very perturbed profile with sharp peak at high altitude Unstable loop when taking into account all subapertures Weighting mandatory for full pupil High cropping (40%) improves performance over weighting but far from ideal


223nm

400nm

300nm

337nm

Non-cooperative Na profile





High flux


Non-cooperative Na profile





High flux


Isolating the high frequency component ->conjugation at 96km + 20 brightest pixels

SR = 8% :(

Brightest pixels amplifies bias inducing high order aberrations

Non-cooperative Na profile : dependance on altitude conjugation





High flux


With spot truncation, conjugation altitude is critical

Non-cooperative Na profile : dependance on altitude conjugation





High flux


Na profile mean altitude

With spot truncation, conjugation altitude is critical but not trivial

Non-cooperative Na profile : expanding the Field-of-View



Subaperture pitch : 50cm Subaperture FOV : variable


High flux


Expanding the FoV removes truncation Performance close to the non-elongated case


Non-cooperative Na profile : expanding the Field-of-View

Expanding the FoV removes truncation Performance close to the non-elongated case

Expanding the FoV by increasing the pixel size (and the LGS FWHM) only slightly degrades the performance



Subaperture pitch : 50cm Subaperture FOV : variable


High flux

38

->Completely discarding 10-40% of the truncated subapertures actually increases Strehl Ratio (depending on Sodium profiles)

->Combining subaperture differential weighting and cropping allow us to reach quasi-ideal performance on most sodium profiles

-> Freak Sodium profiles exist

-> Not an issue when no truncation

-> More small pixels is the best

-> Larger pixels are a good compromise to remove truncation

-> Increase pinhole size, separate the spots, software subaps

Conclusion


39

->Completely discarding 10-40% of the truncated subapertures actually increases Strehl Ratio (depending on Sodium profiles)

->Combining subaperture differential weighting and cropping allow us to reach quasi-ideal performance on most sodium profiles

-> Freak Sodium profiles exist

-> Not an issue when no truncation

-> More small pixels is the best

-> Larger pixels are a good compromise to remove truncation

-> Increase pinhole size, separate the spots, software subaps

Conclusion


The authors thanks the European Research Council for its support through the grant ERC-STG-2015 ICARUS 678777

40

Grazie


223nm

270nm247nm

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap


Conventional SH

Corner SH

Pupil cropping increases

Corner Shack-Hartmann


223nm

270nm247nm





Conventional SH

Corner SH



Not needed


223nm

270nm247nm





Conventional SH

Corner SH






Conventional SH

Corner SH





WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H


44





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without

truncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without tr

uncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases

WFS

sen

sor

With

out t

runc

atio

n

160

pixe

ls

10pi

x/su

bap

160

pixe

ls

10 p

ix/s

ubap

160

pixe

ls

12 p

ix/s

ubap

Con

vent

iona

l SH

Cor

ner S

H

Pup

il cr

oppi

ng in

crea

ses

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

With

out tru

ncatio

n

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventio

nal S

H

Corn

er S

H

Pupil c

roppin

g in

cre

ases

6 LGS configuration

4 LGS configuration



WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H


45





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without

truncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without tr

uncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases

WFS

sen

sor

With

out t

runc

atio

n

160

pixe

ls

10pi

x/su

bap

160

pixe

ls

10 p

ix/s

ubap

160

pixe

ls

12 p

ix/s

ubap

Con

vent

iona

l SH

Cor

ner S

H

Pup

il cr

oppi

ng in

crea

ses

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

With

out tru

ncatio

n

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventio

nal S

H

Corn

er S

H

Pupil c

roppin

g in

cre

ases

6 LGS configuration

4 LGS configuration



WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H


46





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without

truncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without tr

uncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases

WFS

sen

sor

With

out t

runc

atio

n

160

pixe

ls

10pi

x/su

bap

160

pixe

ls

10 p

ix/s

ubap

160

pixe

ls

12 p

ix/s

ubap

Con

vent

iona

l SH

Cor

ner S

H

Pup

il cr

oppi

ng in

crea

ses

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

With

out tru

ncatio

n

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventio

nal S

H

Corn

er S

H

Pupil c

roppin

g in

cre

ases

6 LGS configuration

4 LGS configuration



WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H


47





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without

truncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without tr

uncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases

WFS

sen

sor

With

out t

runc

atio

n

160

pixe

ls

10pi

x/su

bap

160

pixe

ls

10 p

ix/s

ubap

160

pixe

ls

12 p

ix/s

ubap

Con

vent

iona

l SH

Cor

ner S

H

Pup

il cr

oppi

ng in

crea

ses

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

With

out tru

ncatio

n

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventio

nal S

H

Corn

er S

H

Pupil c

roppin

g in

cre

ases

6 LGS configuration

4 LGS configuration



WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H


48





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without

truncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without tr

uncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases

WFS

sen

sor

With

out t

runc

atio

n

160

pixe

ls

10pi

x/su

bap

160

pixe

ls

10 p

ix/s

ubap

160

pixe

ls

12 p

ix/s

ubap

Con

vent

iona

l SH

Cor

ner S

H

Pup

il cr

oppi

ng in

crea

ses

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

With

out tru

ncatio

n

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventio

nal S

H

Corn

er S

H

Pupil c

roppin

g in

cre

ases

6 LGS configuration

4 LGS configuration



WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H


49





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without

truncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without tr

uncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases

WFS

sen

sor

With

out t

runc

atio

n

160

pixe

ls

10pi

x/su

bap

160

pixe

ls

10 p

ix/s

ubap

160

pixe

ls

12 p

ix/s

ubap

Con

vent

iona

l SH

Cor

ner S

H

Pup

il cr

oppi

ng in

crea

ses

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

With

out tru

ncatio

n

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventio

nal S

H

Corn

er S

H

Pupil c

roppin

g in

cre

ases

6 LGS configuration

4 LGS configuration



WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H


50





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without

truncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without tr

uncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases

WFS

sen

sor

With

out t

runc

atio

n

160

pixe

ls

10pi

x/su

bap

160

pixe

ls

10 p

ix/s

ubap

160

pixe

ls

12 p

ix/s

ubap

Con

vent

iona

l SH

Cor

ner S

H

Pup

il cr

oppi

ng in

crea

ses

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

With

out tru

ncatio

n

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventio

nal S

H

Corn

er S

H

Pupil c

roppin

g in

cre

ases

6 LGS configuration

4 LGS configuration



WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H


51





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without

truncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without tr

uncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases

WFS

sen

sor

With

out t

runc

atio

n

160

pixe

ls

10pi

x/su

bap

160

pixe

ls

10 p

ix/s

ubap

160

pixe

ls

12 p

ix/s

ubap

Con

vent

iona

l SH

Cor

ner S

H

Pup

il cr

oppi

ng in

crea

ses

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

With

out tru

ncatio

n

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventio

nal S

H

Corn

er S

H

Pupil c

roppin

g in

cre

ases

6 LGS configuration

4 LGS configuration



WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H


52





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without

truncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases





Conventional SH

Corner SH


WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

Without tr

uncation

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventional S

H

Corn

er

SH

Pupil

cro

ppin

g incre

ases

WFS

sen

sor

With

out t

runc

atio

n

160

pixe

ls

10pi

x/su

bap

160

pixe

ls

10 p

ix/s

ubap

160

pixe

ls

12 p

ix/s

ubap

Con

vent

iona

l SH

Cor

ner S

H

Pup

il cr

oppi

ng in

crea

ses

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH


WF

S s

ensor

With

out tru

ncatio

n

160 p

ixels

10pix

/subap

160 p

ixels

10 p

ix/s

ubap

160 p

ixels

12 p

ix/s

ubap

Conventio

nal S

H

Corn

er S

H

Pupil c

roppin

g in

cre

ases

6 LGS configuration

4 LGS configuration

Corner SH always better than conventional SH for a given # of subapertures


lgs spot truncation mitigation in elt wide field …...lgs spot truncation mitigation in elt wide...

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