characterizing lenslet arrays for the keck adaptive optics system laboratory for adaptive optics...
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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."