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Palomar TomographPalomar Tomograph

V. VelurV. Velur11, B. Platt, B. Platt22, M. Britton, M. Britton1, 1, R. DekanyR. Dekany11

1 1 Caltech Optical Observatories, California Institute of Caltech Optical Observatories, California Institute of TechnologyTechnology

2 2 Interferometry and Large Optics, Jet Propulsion Interferometry and Large Optics, Jet Propulsion LaboratoryLaboratory

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Introduction:Introduction:

Palomar Tomograph (PT) is a compact multiple Palomar Tomograph (PT) is a compact multiple guide star wavefront sensor system that can be guide star wavefront sensor system that can be used to confirm tomographic wavefront sensing used to confirm tomographic wavefront sensing algorithms algorithms

4 Hartmann Shack low noise CCD based 4 Hartmann Shack low noise CCD based wavefront sensors wavefront sensors (three 16x16 sub-apertures, one 3x3 sub-(three 16x16 sub-apertures, one 3x3 sub-aperture) excluding the PALAO active high order wavefront sensor.aperture) excluding the PALAO active high order wavefront sensor.

PALAO also has a dedicated 16x16 SHWFS that PALAO also has a dedicated 16x16 SHWFS that feeds data to a real time computerfeeds data to a real time computer

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Principle of operation of the Principle of operation of the MGSUMGSU

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The “bird-of-prey” (BoP)The “bird-of-prey” (BoP)

Penta prism

collimatorLenslet array

Field lens

Focusing lens

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Scimeasure’s Little Joe Camera with CCD39 chip

XY stage and sleeve

A single Hartmann Shack WFS channel

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The MGSU/ tomograph assembly:

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38.1 +- 0.5 mm

5.7 +- 0.2 mm

3.3 +- 0.2 mm

8.4 +/- 0.2 mm

Anti-reflection coating

(450-900nm)

High-reflectivity (R>99%)

"sodium dichroic" spots (x2)

589.2 nm +- 0.1 nm

(otherwise transmissive)

Application uses dichroic w/

angle of incidence ~ 15 deg

High-reflectivity (R>95%)

"all reflective" spot

for 450-900nm

2.0 +- 0.5 mm

Front surface flat

(to /4 rms over 90%

clear aperture)

Back surface convex

w/ radius

R = 10,000 mm +- 1,000mm

(optical-to-mechanical

centration +- 3 mm)

Back surface broadband

anti-reflection coat for

450-900nm

Thin lens

made of BK7

(edge bevel typ. 1mm)

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Spots on the focal plane array:Spots on the focal plane array:(4x4 pixels/sub-ap., 16x16 spots aligned FPA with >0.1 pixel RMS offset)(4x4 pixels/sub-ap., 16x16 spots aligned FPA with >0.1 pixel RMS offset)

http://eraserhead.caltech.edu/palomar/MGSU/lab_data/lab.html

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Salient features of the PTSalient features of the PT

The system can be used with the PALAO tip-tilt and high order AO loop closed or with both or The system can be used with the PALAO tip-tilt and high order AO loop closed or with both or either being open using low noise CCD based SHWFS. We can record data 50-2000 Hz.either being open using low noise CCD based SHWFS. We can record data 50-2000 Hz.

3.2 Terabytes of total data storage space with two SCSI Ultra 160/RAID on two striped RAID disks 3.2 Terabytes of total data storage space with two SCSI Ultra 160/RAID on two striped RAID disks that can record data at 2000 Hz from 4 cameras acquiring 14 bit data from 64x64 pixels. Data is that can record data at 2000 Hz from 4 cameras acquiring 14 bit data from 64x64 pixels. Data is compressed using custom lossless compression format and can be extracted to fits image with compressed using custom lossless compression format and can be extracted to fits image with time tags.time tags.

BoPs can acquire guide stars over a continuous 90 arc-sec. diameter field. The optical train is BoPs can acquire guide stars over a continuous 90 arc-sec. diameter field. The optical train is designed to be telecentric over this range so that pupil shear is >1.2% (2 microns) at the lenslet designed to be telecentric over this range so that pupil shear is >1.2% (2 microns) at the lenslet pupil (size=1.728 mm) over the FoV.pupil (size=1.728 mm) over the FoV.

Linux based camera control interface and motion control. All control schemes are written in Linux based camera control interface and motion control. All control schemes are written in C/C++. All control code is checked into CVS repository with version control. Documentation and C/C++. All control code is checked into CVS repository with version control. Documentation and user manuals that are available via. www. ssh-agent, ssh-add help us to talk to all cameras from user manuals that are available via. www. ssh-agent, ssh-add help us to talk to all cameras from one shell.one shell.

A 5 ft high commercial 19” rack is populated with a KVM, a 1U rack mounted monitor, 10 Mbps A 5 ft high commercial 19” rack is populated with a KVM, a 1U rack mounted monitor, 10 Mbps network link, a network power switch etc for ease of operation. Newport’s latest LTA series high network link, a network power switch etc for ease of operation. Newport’s latest LTA series high speed actuators used to pick off guide stars with one motor controller controlling all 8 axes.speed actuators used to pick off guide stars with one motor controller controlling all 8 axes.

A custom timing module can be used to trigger as many as 6 cameras to run at integral frame A custom timing module can be used to trigger as many as 6 cameras to run at integral frame rates in a synchronous fashion. This can be used when guide stars are of different brightness or rates in a synchronous fashion. This can be used when guide stars are of different brightness or to study variations in time of the wavefront sensed from each pick off arm. to study variations in time of the wavefront sensed from each pick off arm.

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PerformancePerformance

We have successfully locked on a Tempel 1 (18 magnitude comet We have successfully locked on a Tempel 1 (18 magnitude comet ((extended object)extended object)) at 2.0 air-masses with the 3x3 SHWFS built in the ) at 2.0 air-masses with the 3x3 SHWFS built in the same fashion. same fashion.

PALAO HOWFS performance PALAO HOWFS performance

Bright guide star Strehls as high as 80% at 2.2 mmBright guide star Strehls as high as 80% at 2.2 mm

Maximum frame rate 2000Hz (<7e- read noise)Maximum frame rate 2000Hz (<7e- read noise)

Limiting magnitude ~13.5mV, 10-15% Strehl at 2.2 mmLimiting magnitude ~13.5mV, 10-15% Strehl at 2.2 mm

Read noise 3.5e- at < 500 fpsRead noise 3.5e- at < 500 fpsMean Wavefront Mean Wavefront 165165 nm nm

Typical read noise for e2V’s CCD 39 chips is 3eTypical read noise for e2V’s CCD 39 chips is 3e--s at 500 Hz and 7es at 500 Hz and 7e--s at s at 2000 Hz2000 Hz

In parallel - Matthew’s work on modeling anisoplatismIn parallel - Matthew’s work on modeling anisoplatism

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Measurement error vs. sub-ap diameter, for ro(0.5 micron) =0.15 m, 3e-s of read noise and system transmission=0.36

Combined measurement error and fitting error vs. sub-ap. Diameter, for ro(0.5 micron) =0.15 m, 3e-s of read noise and system transmission=0.36. (Each curve is truncated by fitting error term, indicating that there is no star brightness that results in that level of wavefront measurement error.)

After R. Dekany et al., 2001 Beyond conventional adaptive optics, Venice, Italy

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3

0

nmSNR

d

rphase

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17.06

5

0

nmr

Dfit

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Laboratory set-up:Laboratory set-up:

Poin

t so

urc

e

colli

mato

r

iris

Focu

sing lens

F#1

5.4

focu

s

CC

D c

am

era

w

/ B

oP

Alig

nm

ent

tele

scope

Axis

definin

g

iris

hold

er

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Custom BoP alignment jig:Custom BoP alignment jig:

Gimbal mount

5 axis stage

5 axis stage

Lockable XY and focus stage

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Camera simulator with reticle:Camera simulator with reticle:

Grid to simulate CCD pixels

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Camera controllers and data recording:Camera controllers and data recording:8 a

xis

moto

r co

ntr

olle

r

CC

D c

am

era

con

trolle

rs

Netw

ork

pow

er

swit

ch

KV

M v

ideo s

wit

ch

1U

rack

-moun

table

monit

or

3 x

dell

1U

PC

s w

ith S

CS

I H

DD

and

Ult

ra S

CSI 160

port

3.2

Tera

byte

RA

ID a

rray

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Current status:Current status:

3 BoPs aligned individually3 BoPs aligned individually The data acquisition system is ready with The data acquisition system is ready with

synchronous recording capabilitysynchronous recording capability

To do:To do: Mount the 4 BoPs in the MGSU cageMount the 4 BoPs in the MGSU cage Mount penta prisms and alignMount penta prisms and align Solve frame rate issues with cameras.Solve frame rate issues with cameras. 7 work days of installation schedule (JPL – Chris 7 work days of installation schedule (JPL – Chris

Shelton and Jennifer Roberts)Shelton and Jennifer Roberts)

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Web-site/ documentation:Web-site/ documentation:

http://eraserhead.caltech.edu/palomar/MGSU/MGSU.html