Transcript A Pyramid WFS For LBT AGW Unit

Adaptive Secondary
1st Light AO 4 LBT
MMT Unit
Pyramid WFS
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The two main system characteristic
Adaptive Secondary
Pyramid WFS
WFS camera
EEV39/L3CCD
MMT Unit
MMT336 @MMT
LBT AdSec unit: LBT672
672 actuators
1ms average settling time
Perform WF reconstruction
Acquisition
camera
WFS path
ACQ. Camera
path
WFS board (300x400) moveable for source acq.
Adj. samp. 30x30,15x15,10x10…(on-chip binning)
RON 3.5 e-@650fps
Lim R mag: 16.7 (0.2 on axis SR, 0.6” r0) 2
Use of LLLCCD CCD60 128x128
ELTs 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-
Fundings form European Community
JRA1: High Order WFS comparison
: Development of Adaptive secondaries having 1500 acts.
FP6 : Co-phasing sensor to test at VLT (APE experiment)
: Development of adaptive segments
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Adaptive Primary: OWL case
Using AdSec technique for OWL [pitch 10-100mm]
Adaptive segments
for M1 or M2 ?
P. Dierickx, SPIE 2002, Hawaii
OWL
M6 2.5m (0km)
act. Pitch 27mm
6060 acts
OWL optical train
M1
100m
M2
33.5m
M3
8.2m
M4
8.1m
M5
4.2 m
M6
2.4m
Spherical
Flat
Aspherical
Aspherical
Aspheric
Elliptical
M5
M6
24 conj. @ 7.8km
42 conj. @ 0km
4.2m
2.4m
1
3
12
12
24
42
M5 4.2mfitting
(7.8km) error 290nm (Kband)
Overall
act. Pitch 80mm
2190 acts
K band Adaptive surfaces
courtesy A. Riccardi
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Co-Phasing Using Pyramid Sensor
PWFS
Diff. Pist
unit
FISBA
PWFS (2)
assembly
The lab unit devoted to introduce
A differential piston
Aim of the set up is to
measure at the same time
a certain differential piston
introduced using (3) with
the two instrument FISBA (1)
and PWFS (2).
Unit for (3)
Differential
piston
FISBA interf.
actuator for cube
Unit (1)
displacements
Reflecting surfaces
of the cubes
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WFS signal versus differential piston
Pupil images on CCD
Initial signal value
End signal value
2D signal from pupils
time
Dinamical behaviour of the DP signal on a single pixel
when the DP is changing in time of more than 4 p. Signal
computation uses the same formula used for wavefront
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Derivative estimation
Differantial piston measurement accuracy
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).
RMS of pyramid
measurement with
respect to fitting
values is 15.8 nm
(9 deg in phase angle)
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Pyramid Sensor sensitivity
0.40
Signal amplitude [a.u.]
0.35
0.30
Signal amplitude measured in lab as a
0.25
function of the tilt modulation showing
0.20
an inversely proportional law.
0.15
0.10
0.05
100
200
300
400
500
600
700
800
Radius of modulation [m]
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
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