LGS spot truncation mitigation in ELTs: optimizing the pixel usage

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

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

2AO4ELT 2017

3

LLT

D e t e c t o r plane

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

AO4ELT 2017

4

• À la Diolaiti/Schreiber, we simulate elongated spots (normalized by the Na profile intensity)

• Compute the centroid of each sub-aperture, and project the resulting wave-front on Zernikes

• No elongation: no aberration

• No truncation: Tip/Tilt/Focus only

Impact of truncation on a single WFSAl

titu

de

Time

AO4ELT 2017

5

(blue = peak; error bar = rms ; histogram = avg ; red = cumulative of avg)

Impact of truncation on a single WFSAl

titu

de

Time

• Select 11 Na profiles showing a large variety of configurations

• For each profile, and each time, compute the residual aberrations (for a single WFS)

AO4ELT 2017

6

Impact of truncation on LTAOAl

titu

de

Time

• 6 LGS • No turbulence • MMSE reconstructor • 42’’ radius asterism

(histogram = avg ; red = cumulative of avg ; blue = 30nm and 50nm cutoff)

AO4ELT 2017

7

Need for a Truth Sensor but aberrations are mostly low order => 10x10 subapertures on a truth sensor should be enough on

average but on very perturbed profiles…

Impact of truncation on LTAOAl

titu

de

Time

(histogram = avg ; red = cumulative of avg ; blue = 30nm and 50nm cutoff)

AO4ELT 2017

• 6 LGS • No turbulence • MMSE reconstructor • 42’’ radius asterism

(more on tomographic errors in T. Fusco’s talk this afternoon)

Elongated spots cropping

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

8AO4ELT 2017

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

9

Elongated spots cropping

AO4ELT 2017

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)

Not truncated

Highly truncatedPartially truncated

pupcrop=25%

10

Elongated spots cropping

AO4ELT 2017

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)

Not truncated

Partially truncatedHighly truncated

pupcrop=50%

Killer for 1 WFS…

11

Elongated spots cropping

AO4ELT 2017

12

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)

pupcrop=10%

pupcrop=30%

WFS1 WFS2 WFS3 WFS4

But we have redundancy

12

Elongated spots cropping

AO4ELT 2017

13

LLT

D e t e c t o r plane

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 (Y. Ono poster P3059, Thursday)

E2E simulations (OOMAO)

AO4ELT 2017

Full E-ELT simulation: Pupil diameter : 37m

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

Elongated spots cropping

AO4ELT 2017 14

Full E-ELT simulation: Pupil diameter : 37m

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

Elongated spots cropping

AO4ELT 2017 15

Full E-ELT simulation: Pupil diameter : 37m

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

Elongated spots cropping

AO4ELT 2017 16

Full E-ELT simulation: Pupil diameter : 37m

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

Elongated spots cropping

AO4ELT 2017 17

Full E-ELT simulation: Pupil diameter : 37m

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

Elongated spots cropping

AO4ELT 2017 18

Full E-ELT simulation: Pupil diameter : 37m

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

Elongated spots cropping

AO4ELT 2017 19

Full E-ELT simulation: Pupil diameter : 37m

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

Elongated spots cropping

AO4ELT 2017 20

Full E-ELT simulation: Pupil diameter : 37m

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

Elongated spots cropping

AO4ELT 2017 21

Full E-ELT simulation: Pupil diameter : 37m

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

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

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

Elongated spots cropping

223nm

270nm247nm

AO4ELT 2017 22

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

AO4ELT 2017 23

Differential subaperture weighting

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

AO4ELT 2017 24

Differential subaperture weighting

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

AO4ELT 2017 25

Differential subaperture weighting

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

AO4ELT 2017 26

223nm

Subaperture weighting+cropping

Full E-ELT simulation: Pupil diameter : 37m

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

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

(%)

AO4ELT 2017 27

SODIUM DENSITY PROFILE VARIATIONS

21Pfrommer and Hickson 2011

13.7% 18.6% 16.7%

15.8% 15.3% 11.2%

8.7%

Subaperture weighting+cropping

AO4ELT 2017 28

226nm

234nm

223nm

Subaperture weighting+cropping

Full E-ELT simulation: Pupil diameter : 37m

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

Narrow spot mostly within the subaperture even opposite from LLT

Weighting over-regularizes already good information

Stre

hl in

K-b

and

(%)

AO4ELT 2017 29

223nm

270nm

238nm247nm

Subaperture weighting+cropping

Full E-ELT simulation: Pupil diameter : 37m

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

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

Stre

hl in

K-b

and

(%)

AO4ELT 2017 30

223nm

275nm

226nm

257nm

Subaperture weighting+cropping

Full E-ELT simulation: Pupil diameter : 37m

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

Differential weighting gives almost ideal performance

Stre

hl in

K-b

and

(%)

AO4ELT 2017 31

223nm

265nm

237nm247nm

Subaperture weighting+cropping

Full E-ELT simulation: Pupil diameter : 37m

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

WFE due to elongation reduced from 143nm to 80nm RMS when using subaperture differential weighting

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

Stre

hl in

K-b

and

(%)

AO4ELT 2017 32

223nm

335nm

238nm 250nm233nm

Subaperture weighting+cropping

Full E-ELT simulation: Pupil diameter : 37m

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

WFE due to elongation reduced from 250nm to 83nm RMS when using subaperture differential weighting

WFE reduced to 67nm RMS when combining weighting and cropping

Stre

hl in

K-b

and

(%)

AO4ELT 2017 33

223nm

349nm

318nm330nm

Subaperture weighting+cropping

Full E-ELT simulation: Pupil diameter : 37m

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

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

(%)

AO4ELT 2017 34

223nm

400nm

300nm

337nm

Subaperture weighting+cropping

Full E-ELT simulation: Pupil diameter : 37m

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

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

AO4ELT 2017 35

Truth sensor

How many modes do we need to measure to remain below a prescribed WFE due to spot elongation ?

AO4ELT 2017 36

Truth sensor

How many modes do we need to measure to remain below a prescribed WFE due to spot elongation ?

AO4ELT 2017 37

8x8 truth sensor sufficient to remain below 10nm at all times

Truth sensor

How many modes do we need to measure to remain below a prescribed WFE due to spot elongation ?

AO4ELT 2017 38

Single Top hat Double Very

narrowMulti peak

Very wide

Top hat +peak

10nm z1 z10 z14 z14 z28 z42 z56

20nm z1 z1 z1 z1 z1 z42 z42

30nm z1 z1 z1 z1 z1 z42 z42

40nm z1 z1 z1 z1 z1 z28 z28

50nm z1 z1 z1 z1 z1 z28 z28

223nm

270nm247nm

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

Corner Shack-Hartmann

AO4ELT 2017 39

223nm

270nm247nm

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

Corner Shack-Hartmann

Not needed

AO4ELT 2017 40

223nm

270nm247nm

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

Corner Shack-Hartmann

AO4ELT 2017 41

Corner Shack-Hartmann

WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H

Pupil cropping increases

AO4ELT 2017 42

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

Pupil cropping increases

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 Shack-Hartmann

WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H

Pupil cropping increases

AO4ELT 2017 43

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

Pupil cropping increases

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 Shack-Hartmann

WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H

Pupil cropping increases

AO4ELT 2017 44

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

Pupil cropping increases

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 Shack-Hartmann

WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H

Pupil cropping increases

AO4ELT 2017 45

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

Pupil cropping increases

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 Shack-Hartmann

WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H

Pupil cropping increases

AO4ELT 2017 46

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

Pupil cropping increases

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 Shack-Hartmann

WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H

Pupil cropping increases

AO4ELT 2017 47

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

Pupil cropping increases

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 Shack-Hartmann

WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H

Pupil cropping increases

AO4ELT 2017 48

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

Pupil cropping increases

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 Shack-Hartmann

WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H

Pupil cropping increases

AO4ELT 2017 49

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

Pupil cropping increases

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 Shack-Hartmann

WFS

sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional S

H

Corner S

H

Pupil cropping increases

AO4ELT 2017 50

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

WFS sensorWithout truncation

160 pixels10pix/subap

160 pixels10 pix/subap

160 pixels12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

Pupil cropping increases

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

Pupil cropping increases

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

51

->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

-> Help release constraints on Truth Sensor design: 8(x8) is enough !

-> Corner Shack-Hartmann to optimize pixel usage

AO4ELT 2017

Conclusion

AO4ELT 2017 52

- Thorough analysis of more parameters (truncation, d/r0, central obscuration, asterism diameter, #LGS…)

- Advanced centroiding algorithms/strategies

- Actual ELT M4 geometry (see N. Schwartz talk tomorrow 12:30)

- Temporal aspects, sodium profil evolution during the night

On-going work

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

AO4ELT 2017 53

Gracias