LGS spot truncation mitigation in ELTs: optimizing the pixel usage

(1)

LGS spot truncation mitigation in ELTs:

optimizing the pixel usage

L.Blanco

¹

, C. Correia

¹

, T. Fusco

²

, B. Neichel

¹

, Y. Ono

¹

1 Laboratoire d’Astrophysique de Marseille (UMR7326 - CNRS-INSU, Université d’Aix-Marseille)

2 ONERA - The French Aerospace Lab

(2)

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

2 AO4ELT 2017

(3)

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)

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 WFS

Alt it ude

Time

AO4ELT 2017

(5)

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

Impact of truncation on a single WFS

Alt it ude

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)

6 Impact of truncation on LTAO

Alt it ude

Time

• 6 LGS

• No turbulence

• MMSE reconstructor

• 42’’ radius asterism

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

AO4ELT 2017

(7)

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 LTAO

Alt it ude

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)

(8)

Elongated spots cropping

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

8 AO4ELT 2017

(9)

What if we completely discarded the biased measurements from the subapertures with the most truncated spots ? Spot elongation ∝ distance from laser launch telescope D LLT

->we ‘crop’ the subapertures at D LLT > D x (1-pup crop )

Highly truncated Partially truncated

Not truncated

pup crop =0

9 Elongated spots cropping

AO4ELT 2017

(10)

What if we completely discarded the biased measurements from the subapertures with the most truncated spots ? Spot elongation ∝ distance from laser launch telescope D LLT

->we ‘crop’ the subapertures at D LLT > D x (1-pup crop )

Not truncated

Highly truncated Partially truncated

pup crop =25%

10 Elongated spots cropping

AO4ELT 2017

(11)

What if we completely discarded the biased measurements from the subapertures with the most truncated spots ? Spot elongation ∝ distance from laser launch telescope D LLT

->we ‘crop’ the subapertures at D LLT > D x (1-pup crop )

Not truncated

Partially truncated

Highly truncated

pup crop =50%

Killer for 1 WFS…

11 Elongated spots cropping

AO4ELT 2017

(12)

12 What if we completely discarded the biased measurements from the subapertures with the most truncated spots ? Spot elongation ∝ distance from laser launch telescope D LLT

->we ‘crop’ the subapertures at D LLT > D x (1-pup crop )

pup crop =10%

pup crop =30%

WFS 1 WFS 2 WFS 3 WFS 4

But we have redundancy

12 Elongated spots cropping

AO4ELT 2017

(13)

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

(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 14

(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 15

(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 16

(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 17

(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 18

(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 19

(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 20

(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

Elongated spots cropping

AO4ELT 2017 21

(22)

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 270nm

247nm

AO4ELT 2017 22

152nm 106nm

(23)

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

(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 24

(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 25

(26)

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

(27)

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

270nm

247nm

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

subaperture differential weighting but Na profile not always bimodal !

238nm

St re hl i n K- ba nd ( % )

AO4ELT 2017 27

(28)

SODIUM DENSITY PROFILE VARIATIONS

21 Pfrommer and Hickson 2011

13.7% 18.6% 16.7%

15.8% 15.3% 11.2%

8.7%

Subaperture weighting+cropping

AO4ELT 2017 28

(29)

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

St re hl i n K- ba nd ( % )

AO4ELT 2017 29

(30)

223nm

270nm 238nm

247nm

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

St re hl i n K- ba nd ( % )

AO4ELT 2017 30

(31)

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

St re hl i n K- ba nd ( % )

AO4ELT 2017 31

(32)

223nm

265nm 237nm

247nm

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

St re hl i n K- ba nd ( % )

AO4ELT 2017 32

(33)

223nm

335nm

238nm 250nm

233nm

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

St re hl i n K- ba nd ( % )

AO4ELT 2017 33

(34)

223nm

349nm

318nm 330nm

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

St re hl i n K- ba nd ( % )

AO4ELT 2017 34

(35)

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

St re hl i n K- ba nd ( % )

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

(36)

Truth sensor

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

AO4ELT 2017 36

(37)

Truth sensor

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

AO4ELT 2017 37

(38)

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

narrow Multi

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

(39)

223nm 270nm 247nm

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

Corner Shack-Hartmann

AO4ELT 2017 39

(40)

223nm 270nm 247nm

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

Corner Shack-Hartmann

No t needed

AO4ELT 2017 40

(41)

223nm 270nm 247nm

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 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

Corner Shack-Hartmann

AO4ELT 2017 41

(42)

Corner Shack-Hartmann

WFS

senso r

Witho

ut trunca

tion

160 pixel

s

10pix/

suba

p

160 pixels

10 pix

/sub ap

160

pixels

12 pix/

sub ap

Conven

tiona

l SH

Cor ner

SH

Pupil crop

ping

increase s

AO4ELT 2017 42

WFS sensor Without truncation

160 pixels 10pix/subap

160 pixels 10 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

160 pixels 12 pix/subap 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

Pupil cropping increase

s

WFS senso r

Witho ut trunca

tion

160 pixel

s

10p ix/subap 160

pixels

10 pix

/sub ap

160 pixels 12 pix/

sub ap Conven

tional S H

Cor ner

SH

Pupi l crop

pin g increase

s

FS W

senso r

itho W

trunca ut tion

160 ixel p s

10p

su ix/

p ba

160 pixels

pix 10

/sub ap

0 16

pixels

pix/ 12

sub ap

Con ven na tio

H l S

Cor ner SH Pupi l crop

g pin

increase s

senso WFS

r

Witho ut trunca tion

pixel 160

s

ix/su 10p

bap

pixels 160

pix/sub 10

ap

pixels 160

pix/ 12

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nal S H Corner SH

l crop Pupi

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FW

sS

enso

r

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p160

ixel s ix/ 10p basu p

160 xels pi pix 10

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onC ven

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Hl S Cor

ner HS

upiP l crop pin ing crease

s

6 LGS configuration

4 LGS configuration

(43)

Corner Shack-Hartmann

WFS

senso r

Witho

ut trunca

tion

160 pixel

s

10pix/

suba

p

160 pixels

10 pix

/sub ap

160

pixels

12 pix/

sub ap

Conven

tiona

l SH

Cor ner

SH

Pupil crop

ping

increase s

AO4ELT 2017 43

Corner SH

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

s

WFS senso r

Witho ut trunca

tion

160 pixel

s

10p ix/subap 160

pixels

10 pix

/sub ap

160 pixels 12 pix/

sub ap Conven

tional S H

Cor ner

SH

Pupi l crop

pin g increase

s

FS W

senso r

itho W

trunca ut tion

160 ixel p s

10p

su ix/

p ba

160 pixels

pix 10

/sub ap

0 16

pixels

pix/ 12

sub ap

Con ven na tio

H l S

g pin

increase s

senso WFS

r

pixel 160

s

ix/su 10p

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pixels 160

pix/sub 10

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pixels 160

pix/ 12

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ventio Con

nal S H Corner SH

l crop Pupi

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sS

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160 xels pi pix 10

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Hl S Cor

ner HS

s

6 LGS configuration

4 LGS configuration

(44)

Corner Shack-Hartmann

WFS

senso r

Witho

ut trunca

tion

160 pixel

s

10pix/

suba

p

160 pixels

10 pix

/sub ap

160

pixels

12 pix/

sub ap

Conven

tiona

l SH

Cor ner

SH

Pupil crop

ping

increase s

AO4ELT 2017 44

Corner SH

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

s

WFS senso r

Witho ut trunca

tion

160 pixel

s

10p ix/subap 160

pixels

10 pix

/sub ap

160 pixels 12 pix/

sub ap Conven

tional S H

Cor ner

SH

Pupi l crop

pin g increase

s

FS W

senso r

itho W

trunca ut tion

160 ixel p s

10p

su ix/

p ba

160 pixels

pix 10

/sub ap

0 16

pixels

pix/ 12

sub ap

Con ven na tio

H l S

g pin

increase s

senso WFS

r

pixel 160

s

ix/su 10p

bap

pixels 160

pix/sub 10

ap

pixels 160

pix/ 12

subap

ventio Con

nal S H Corner SH

l crop Pupi

ping increase s

FW

sS

enso

r

ithoW

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p160

160 xels pi pix 10

/sub

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onC ven

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Hl S Cor

ner HS

s

6 LGS configuration

4 LGS configuration

(45)

Corner Shack-Hartmann

WFS

senso r

Witho

ut trunca

tion

160 pixel

s

10pix/

suba

p

160 pixels

10 pix

/sub ap

160

pixels

12 pix/

sub ap

Conven

tiona

l SH

Cor ner

SH

Pupil crop

ping

increase s

AO4ELT 2017 45

Corner SH

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

s

WFS senso r

Witho ut trunca

tion

160 pixel

s

10p ix/subap 160

pixels

10 pix

/sub ap

160 pixels 12 pix/

sub ap Conven

tional S H

Cor ner

SH

Pupi l crop

pin g increase

s

FS W

senso r

itho W

trunca ut tion

160 ixel p s

10p

su ix/

p ba

160 pixels

pix 10

/sub ap

0 16

pixels

pix/ 12

sub ap

Con ven na tio

H l S

g pin

increase s

senso WFS

r

pixel 160

s

ix/su 10p

bap

pixels 160

pix/sub 10

ap

pixels 160

pix/ 12

subap

ventio Con

nal S H Corner SH

l crop Pupi

ping increase s

FW

sS

enso

r

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160 xels pi pix 10

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Hl S Cor

ner HS

s

6 LGS configuration

4 LGS configuration

(46)

Corner Shack-Hartmann

WFS

senso r

Witho

ut trunca

tion

160 pixel

s

10pix/

suba

p

160 pixels

10 pix

/sub ap

160

pixels

12 pix/

sub ap

Conven

tiona

l SH

Cor ner

SH

Pupil crop

ping

increase s

AO4ELT 2017 46

Corner SH

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

s

WFS senso r

Witho ut trunca

tion

160 pixel

s

10p ix/subap 160

pixels

10 pix

/sub ap

160 pixels 12 pix/

sub ap Conven

tional S H

Cor ner

SH

Pupi l crop

pin g increase

s

FS W

senso r

itho W

trunca ut tion

160 ixel p s

10p

su ix/

p ba

160 pixels

pix 10

/sub ap

0 16

pixels

pix/ 12

sub ap

Con ven na tio

H l S

g pin

increase s

senso WFS

r

pixel 160

s

ix/su 10p

bap

pixels 160

pix/sub 10

ap

pixels 160

pix/ 12

subap

ventio Con

nal S H Corner SH

l crop Pupi

ping increase s

FW

sS

enso

r

ithoW

tion truncaut

p160

160 xels pi pix 10

/sub

ap 16

onC ven

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Hl S Cor

ner HS

s

6 LGS configuration

4 LGS configuration

(47)

Corner Shack-Hartmann

WFS

senso r

Witho

ut trunca

tion

160 pixel

s

10pix/

suba

p

160 pixels

10 pix

/sub ap

160

pixels

12 pix/

sub ap

Conven

tiona

l SH

Cor ner

SH

Pupil crop

ping

increase s

AO4ELT 2017 47

Corner SH

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

s

WFS senso r

Witho ut trunca

tion

160 pixel

s

10p ix/subap 160

pixels

10 pix

/sub ap

160 pixels 12 pix/

sub ap Conven

tional S H

Cor ner

SH

Pupi l crop

pin g increase

s

FS W

senso r

itho W

trunca ut tion

160 ixel p s

10p

su ix/

p ba

160 pixels

pix 10

/sub ap

0 16

pixels

pix/ 12

sub ap

Con ven na tio

H l S

g pin

increase s

senso WFS

r

pixel 160

s

ix/su 10p

bap

pixels 160

pix/sub 10

ap

pixels 160

pix/ 12

subap

ventio Con

nal S H Corner SH

l crop Pupi

ping increase s

FW

sS

enso

r

ithoW

tion truncaut

p160

160 xels pi pix 10

/sub

ap 16

onC ven

tiona

Hl S Cor

ner HS

s

6 LGS configuration

4 LGS configuration

(48)

Corner Shack-Hartmann

WFS

senso r

Witho

ut trunca

tion

160 pixel

s

10pix/

suba

p

160 pixels

10 pix

/sub ap

160

pixels

12 pix/

sub ap

Conven

tiona

l SH

Cor ner

SH

Pupil crop

ping

increase s

AO4ELT 2017 48

Corner SH

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

s

WFS senso r

Witho ut trunca

tion

160 pixel

s

10p ix/subap 160

pixels

10 pix

/sub ap

160 pixels 12 pix/

sub ap Conven

tional S H

Cor ner

SH

Pupi l crop

pin g increase

s

FS W

senso r

itho W

trunca ut tion

160 ixel p s

10p

su ix/

p ba

160 pixels

pix 10

/sub ap

0 16

pixels

pix/ 12

sub ap

Con ven na tio

H l S

g pin

increase s

senso WFS

r

pixel 160

s

ix/su 10p

bap

pixels 160

pix/sub 10

ap

pixels 160

pix/ 12

subap

ventio Con

nal S H Corner SH

l crop Pupi

ping increase s

FW

sS

enso

r

ithoW

tion truncaut

p160

160 xels pi pix 10

/sub

ap 16

onC ven

tiona

Hl S Cor

ner HS

s

6 LGS configuration

4 LGS configuration

(49)

Corner Shack-Hartmann

WFS

senso r

Witho

ut trunca

tion

160 pixel

s

10pix/

suba

p

160 pixels

10 pix

/sub ap

160

pixels

12 pix/

sub ap

Conven

tiona

l SH

Cor ner

SH

Pupil crop

ping

increase s

AO4ELT 2017 49

Corner SH

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

s

WFS senso r

Witho ut trunca

tion

160 pixel

s

10p ix/subap 160

pixels

10 pix

/sub ap

160 pixels 12 pix/

sub ap Conven

tional S H

Cor ner

SH

Pupi l crop

pin g increase

s

FS W

senso r

itho W

trunca ut tion

160 ixel p s

10p

su ix/

p ba

160 pixels

pix 10

/sub ap

0 16

pixels

pix/ 12

sub ap

Con ven na tio

H l S

g pin

increase s

senso WFS

r

pixel 160

s

ix/su 10p

bap

pixels 160

pix/sub 10

ap

pixels 160

pix/ 12

subap

ventio Con

nal S H Corner SH

l crop Pupi

ping increase s

FW

sS

enso

r

ithoW

tion truncaut

p160

160 xels pi pix 10

/sub

ap 16

onC ven

tiona

Hl S Cor

ner HS

s

6 LGS configuration

4 LGS configuration

(50)

Corner Shack-Hartmann

WFS

senso r

Witho

ut trunca

tion

160 pixel

s

10pix/

suba

p

160 pixels

10 pix

/sub ap

160

pixels

12 pix/

sub ap

Conven

tiona

l SH

Cor ner

SH

Pupil crop

ping

increase s

AO4ELT 2017 50

Corner SH

WFS sensor

Without truncation

160 pixels

10pix/subap

160 pixels

10 pix/subap

160 pixels

12 pix/subap

Conventional SH

Corner SH

s

WFS senso r

Witho ut trunca

tion

160 pixel

s

10p ix/subap 160

pixels

10 pix

/sub ap

160 pixels 12 pix/

sub ap Conven

tional S H

Cor ner

SH

Pupi l crop

pin g increase

s

FS W

senso r

itho W

trunca ut tion

160 ixel p s

10p

su ix/

p ba

160 pixels

pix 10

/sub ap

0 16

pixels

pix/ 12

sub ap

Con ven na tio

H l S

g pin

increase s

senso WFS

r

pixel 160

s

ix/su 10p

bap

pixels 160

pix/sub 10

ap

pixels 160

pix/ 12

subap

ventio Con

nal S H Corner SH

l crop Pupi

ping increase s

FW

sS

enso

r

ithoW

tion truncaut

p160

160 xels pi pix 10

/sub

ap 16

onC ven

tiona

Hl S Cor

ner HS

s

6 LGS configuration

4 LGS configuration

Corner SH always better than conventional SH

for a given # of subapertures

(51)

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

(52)

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

(53)