Characterizing Lenslet Arrays for the Keck Adaptive Optics System

Laboratory for Adaptive optics (LAO)UC Santa Cruz

Name: Abubakarr BahHome Institution: Santa Rosa Junior College

Advisor: Dr. Don GavelMentor: Dr. Renate Kupke

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What are Lenslets?• Small lenses (50 um- 1 mm)• Part of an array.• Found in Shack-Hartmann wave front sensors.

Image taken from http://www.ctio.noao.edu

Lenslet on a Shack-Hartmann wavefront sensor

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My Project Information

Characterizing Lenslets arrays for the Keck adaptive optics system:

•Focal Length•Pitch Measurement•Transmission•Lenslet Optical Figure

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Focal length setup

CCD

Pinhole(5 µ)

.633 um

f

Microscope Objective (10x)

Microscope Objective (50x)

Diodelaser

Aperture

Collimatedlight

Lenslet

Computer

Hartmann Spots

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Focal length at a single wavelength (.633 um)

ArrayFocal length spec. (mm)

Focal length Meas. (mm)

Depth of focus (uncertainty)

A 4.9 ± 0.5 4.95 ± 0.39

B 3.1 ± 0.3 3.11 ±0.17

C 2.4 ± 0.2 2.39 ±0.11

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Focal length set up for different Wavelength.

White lightSource

CCD

LensletMicroscope

Objective (10x)

Computer

Microscope Objective (50x)Filter

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Wavelength Vs. Focal length

0

1

2

3

4

5

6

0 100 200 300 400 500 600 700 800 900 1000

Wavelength (um)

Fo

cal

len

gth

(m

m)

Focal length I

Focal length II

Focal length III

Name: Abubakarr Bah

Mentor: Reni Kupke

Date: 7-27-07Lab for Adaptive Optics

US Santa Cruz

WavelengthFocal length

AFocal Length

BFocal length

C

400 4.42 2.90 2.23

500 4.81 3.00 2.42

600 4.92 3.14 2.35

800 4.86 3.02 2.23

700 4.60 3.02 2.46

Focal length at diff. wavelength

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Pitch Measurements:

• Spot Pitch Measurements:

- Same as Focal Length Setup

- Distance b/w Spots

•Pitch Measurements:

- LAO's Olympus microscope- 20 Lenslet at a time

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Focal Spot Pitch

LensletFocal Spot Pitch Spec

(mm)

Focal Spot Pitch Meas.

(mm)RMS Error

A 0.200 0.1996 ± 0.00134

B 0.200 0.1995 ± 0.00088

C 0.200 0.1997 ± 0.00091

10up= towards lenslet III

Right= towards markings.

Pitch Measurements Using the LAO's Olympus microscopeMeasurements were taking 20 lenslet at time

lensletUp

(mm)Down (mm)

Right (mm)

Left (mm) RMS Error

A 4.0000 3.9980 4.0000 4.0000 ± 0.0010

B 4.0000 4.0000 4.0000 4.0000 ± 0.0000

C 4.0000 4.0000 4.0000 3.9660 ± 0.0170

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Transmission of the Lenslets:

Keck Specification:>97 %

EXPERIMENTS:

• Used The UCO Lick Optical Shop's spectrophotometer.• Made a simple optical setup

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Throughput.

White lightSource

Filter Lenslet

Photometer

Pin Hole

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Wavelength Vs. Transmission

0.84

0.86

0.88

0.9

0.92

0.94

0.96

0.98

1

0 200 400 600 800 1000 1200

Wavelength (um)

Perc

en

t T

ran

sm

issio

n

Average1

Average2

Average3

Name: Abubakarr Bah

Mentor: Reni Kupke

Lab for Adaptive Optics

Date: 07-28-07

Min 0.84

Max 1.00

Transmission of Lenslet:

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Pitch Vs Height

-0.5

0

0.5

1

1.5

2

0 50 100 150 200 250 300 350 400 450 500

Pitch (um)

Heig

ht

(um

)

Lenslets optical Figure:

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Conclusions:

. Focal length and Pitch meet specifications

.Transmission meets the specifications within 500-950 nm. Lenslet has a parabolic shape and steps patterns (surprising observation !)

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Acknowledgments

Dr. Don GavelDr. Renate KupkeSandrine ThomasDaren DillonMarco ReinigMembers of the LAO labCenter for Adaptive Optics (CFAO)

This work has been supported by the National Science Foundation Science and Technology Center for Adaptive Optics, managed by the University of California at Santa Cruz under cooperative agreement No. AST - 9876783."