Characterizing Lenslet Arrays for
the Keck Adaptive Optics System
Laboratory for Adaptive optics (LAO)
UC Santa Cruz
Name: Abubakarr Bah
Home Institution: Santa Rosa Junior College
Advisor: Dr. Don Gavel
Mentor: Dr. Renate Kupke
What are Lenslets?
•
•
•
Small lenses (50 um- 1 mm)
Part of an array.
Found in Shack-Hartmann wave front sensors.
Lenslet on a Shack-Hartmann wavefront sensor
Image taken from http://www.ctio.noao.edu
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My Project Information
Characterizing Lenslets arrays for
the Keck adaptive optics system:
•Focal Length
•Pitch Measurement
•Transmission
•Lenslet Optical Figure
3
Focal length setup
Pinhole
(5 µ)
Aperture
Lenslet
.633 um
CCD
Computer
f
Microscope
Diode Objective (10x)
laser
Collimated
light
Hartmann Spots
Microscope
Objective (50x)
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Focal length at a single
wavelength (.633 um)
Depth of
Focal length
focus
Meas. (mm)
(uncertainty)
Array
Focal length
spec. (mm)
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.
Microscope
Objective (50x)
Filter
CCD
White light
Source
Microscope
Objective (10x)
Computer
Lenslet
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Focal length at diff. wavelength
Wavelength
Focal length
A
Focal Length
B
Focal 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
Name: Abubakarr
Bah
Mentor: Reni Kupke
Date: 7-27-07
Lab for Adaptive Optics
US Santa Cruz
Wavelength Vs. Focal length
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Focal length (mm)
5
4
Focal length I
Focal length II
Focal length III
3
2
1
7
0
0
100
200
300
400
500
600
Wavelength (um)
700
800
900
1000
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
Lenslet
Focal 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
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Pitch Measurements Using the LAO's Olympus microscope
Measurements were taking 20 lenslet at time
lenslet
Up
(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
up= towards lenslet III
Right= towards markings
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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.
Filter
Lenslet
Pin Hole
White light
Source
Photometer
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Transmission of Lenslet:
Name: Abubakarr
Bah
Mentor: Reni Kupke
Max 1.00
Lab for Adaptive
Optics
Date: 07-28-07
Wavelength Vs. Transmission
1
0.98
Percent Transmission
0.96
0.94
Average1
Average2
Average3
0.92
0.9
0.88
0.86
0.84
Min 0.84
0
200
400
600
800
1000
1200
Wavelength (um)
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Lenslets optical Figure:
Pitch Vs Height
2
Height (um)
1.5
1
0.5
0
0
50
100
150
200
250
300
350
400
450
500
-0.5
Pitch (um)
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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 Gavel
Dr. Renate Kupke
Sandrine Thomas
Daren Dillon
Marco Reinig
Members of the LAO lab
Center 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."
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