1

11stst Light AO 4 LBT Light AO 4 LBT

Pyramid WFS

Adaptive Secondary

MMT Unit

2

The two main system characteristicThe two main system characteristic

Adaptive Secondary

MMT Unit

LBT AdSec unit: LBT672672 actuators1ms average settling timePerform WF reconstruction

Pyramid WFS

WFS board (300x400) moveable for source acq.Adj. samp. 30x30,15x15,10x10…(on-chip binning)RON 3.5 e-@650fpsLim R mag: 16.7 (0.2 on axis SR, 0.6” r0) Use of LLLCCD CCD60 128x128

MMT336 @MMT

WFS cameraEEV39/L3CCD

Acquisitioncamera

WFS pathACQ. Camera path

3

ELTs application of LBT AO componentsELTs application of LBT AO components

•Adaptive secondaries technologies to be used for adaptive segments for ELTs. •Use of Pyramid WFS as co-phasing sensor for ELTs segmented mirrors•Use of Pyramid sensor as High Order WFS > 100 subapertures•Use of LLL CCD in future ELTs AO system. Needs for many pixels 256x256 and 1Kfps speed with low RON <1e-

JRA1: High Order WFS comparison : Development of Adaptive secondaries having 1500 acts.

Fundings form European Community

FP6 : Co-phasing sensor to test at VLT (APE experiment) : Development of adaptive segments

4

Adaptive Primary: OWL caseAdaptive Primary: OWL caseUsing AdSec technique for OWL [pitch 10-100mm]

OWL

OWL optical trainM1 100m Spherical 1M2 33.5m Flat 3M3 8.2m Aspherical 12M4 8.1m Aspherical 12M5 4.2 m Aspheric 24M6 2.4m Elliptical 42

M5 4.2m 24 conj. @ 7.8km

M6 2.4m 42 conj. @ 0km

courtesy A. Riccardi

M6 2.5m (0km)act. Pitch 27mm6060 acts

M5 4.2m (7.8km)act. Pitch 80mm2190 acts

Adaptive segmentsfor M1 or M2 ?

Overall fitting error 290nm (Kband)Overall fitting error 290nm (Kband)

P. Dierickx, SPIE 2002, Hawaii

K band Adaptive surfaces

5

Co-Phasing Using Pyramid SensorCo-Phasing Using Pyramid Sensor

PWFS (2) assembly

FISBA interf.Unit (1)

Unit for (3) Differentialpiston

FISBADiff. Pistunit

PWFS

Aim of the set up is tomeasure at the same timea certain differential pistonintroduced using (3) withthe two instrument FISBA (1)and PWFS (2).

Reflecting surfacesof the cubes

actuator for cubedisplacements

The lab unit devoted to introduceA differential piston

6

WFS signal versus differential pistonWFS signal versus differential piston

Initial signal value

End signal value

time

Dinamical behaviour of the DP signal on a single pixelwhen the DP is changing in time of more than 4 Signal computation uses the same formula used for wavefront Derivative estimation

Pupil images on CCD

2D signal from pupils

7

Differantial piston measurement accuracyDifferantial piston measurement accuracy

RMS of pyramid measurement with respect to fitting values is 15.8 nm

(9 deg in phase angle)

RMS of pyramid measurement with respect to fitting values is 15.8 nm

(9 deg in phase angle)

Comparison of interferometer and pyramid measurements of the same differential piston,using:

1) LBT pyramid wavefront sensor (Y axis) and

2) FISBA interferometr (X axis).

8

Pyramid Sensor sensitivityPyramid Sensor sensitivity

100 200 300 400 500 600 700 8000.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Sig

nal a

mpl

itude

[a.u

.]

Radius of modulation [m]

Signal amplitude measured in lab as a

function of the tilt modulation showing

an inversely proportional law.

2 3 1 4( , ) ( , ) ( , ) ( , )y

i

I x y I x y I x y I x yS

I

2 3 1 4( , ) ( , ) ( , ) ( , )

yi

I x y I x y I x y I x yS

I

The wavefront error due to pure photon noise can be stimated using the sensitivity measurements. In particular considering a segment of 2.1 m2, a 15 magnitude star and 30 s exposion, we found a residual differential piston error on the wavefront of 7.3 nm

The wavefront error due to pure photon noise can be stimated using the sensitivity measurements. In particular considering a segment of 2.1 m2, a 15 magnitude star and 30 s exposion, we found a residual differential piston error on the wavefront of 7.3 nm