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Characterization of a Characterization of a Bimorph Deformable Mirror Bimorph Deformable Mirror in a Closed Loop Adaptive in a Closed Loop Adaptive Optics System for Vision Optics System for Vision
Science PurposesScience Purposes
Zachary GrahamZachary Graham11 Sophie LautSophie Laut22, David Horsley, David Horsley33, John Werner, John Werner22
11 Hartnell Community College, Salinas, CA Hartnell Community College, Salinas, CA2 2 Department of Ophthalmology and Psychophysics, UC DavisDepartment of Ophthalmology and Psychophysics, UC Davis
3 3 Department of Mechanical and Aeronautical Engineering, UC DavisDepartment of Mechanical and Aeronautical Engineering, UC Davis
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AO in vision scienceAO in vision science
Removes aberrations in the eyeRemoves aberrations in the eye Increases resolving powerIncreases resolving power Allows for more thorough and advanced Allows for more thorough and advanced
study of the eye and brain study of the eye and brain (psychophysics)(psychophysics)
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My ProjectMy Project
To help characterize a mirror for use in a To help characterize a mirror for use in a next generation Adaptive Optics imaging next generation Adaptive Optics imaging systemsystem Helped with the setup of the system Helped with the setup of the system Wrote a program in MATLAB to generate Wrote a program in MATLAB to generate
Zernike mode aberrationsZernike mode aberrations Took data on the mirrorTook data on the mirror
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Next Gen. AO SystemNext Gen. AO System
Will operate in 2 modesWill operate in 2 modes Scanning Laser Ophthalmoscope (SLO)Scanning Laser Ophthalmoscope (SLO) Optical Coherence Tomography (OCT)Optical Coherence Tomography (OCT)
2 Deformable Mirrors2 Deformable Mirrors MEMS and Bimorph will be cascaded in one systemMEMS and Bimorph will be cascaded in one system
Bimorph will replacethe role trial lensesBimorph will replacethe role trial lenses Will remove more aberrationsWill remove more aberrations Computer automatedComputer automated Much more flexibleMuch more flexible
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• Active area : 4 mm x 4 mm• No of actuators : 100• Continuous surface• Stroke (wavefront) : +/- 2 m• Response speed : ~3.5 kHz• Operative voltage : 200 V• Cost : ~ $25,000
Specification :
for high-order aberration correction
The Boston Micromachines MEMS mirror
Relatively small Stroke !
Slide Courtesy of Sophie Laut,
UC Davis Medical Center
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• Active area : 12 mm, round• No of actuators : 35• Continuous surface• Stroke (wavefront) : +/- 40 m• Maximum deflection : +/- 20 m• Response speed : ~4 kHz• Operative voltage : 15-30 V
Specification :
for low-order aberration correction
The AOptix Bimorph deformable mirror
Actuator geometry Usual applications : Optical telecommunication system
High Stroke !
Slide Courtesy of Sophie Laut,
UC Davis Medical Center
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Imaging SetupImaging Setup
Bimorph DM
Hartmann – Shack Wave front sensor
Pupil PlaneLaser
Diode
Telescope 2
= 1
Telescope 1
= 1
System Information
total = 1.00
flatness = /13
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Characterization ProcessCharacterization Process
Control Loop closes and mirror corrects wave front
Before/After data analyzed
Place aberration into system
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Characterization ProcessCharacterization Process
Control Loop closes and mirror corrects wave front
Before/After data analyzed
Place aberration into system
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AberrationsAberrations
Lower order aberrations Lower order aberrations were introduced using trial lenses.were introduced using trial lenses. Cylinder and SphereCylinder and Sphere
Higher ordered aberrationsHigher ordered aberrations Trial lenses cannot be usedTrial lenses cannot be used Generated in MATLABGenerated in MATLAB
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1
1 1.. , ..x xn y yn
n
a
S S S S A
a
Solution Vector (Slope)
Matrix of partial derivatives for all used
zernike modes
Vector of normalized zernike
coefficients
( , ) 2
( , ) 2
ij ij
ij ij
x yx
x f
x yy
y f
Centroid Displacement AlgorithmCentroid Displacement Algorithm
•Starts with a file of reference positions
•Reads the value of each reference Centro id from a matrix of partial derivatives for the particular Fernike mode. and calculates the slope in x and y
•The slope is direcly proportional to the displacement
•The displacement is added to the reference position and logged
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Preparing Simulated AberrationsPreparing Simulated Aberrations
1.1. A specific Zernike mode is pickedA specific Zernike mode is picked
2.2. Maximum detectable amplitude is determinedMaximum detectable amplitude is determined
3.3. Aberrations are generatedAberrations are generated
4.4. Aberrations introduced to the systemAberrations introduced to the system
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Characterization ProcessCharacterization Process
Control Loop closes and mirror corrects wave front
Before/After data analyzed
Place aberration into system
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AO in ActionAO in Action
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Problems with trial lensesProblems with trial lenses
The lenslet array could not resolve more The lenslet array could not resolve more than 1.8 diopters of error (defocus)than 1.8 diopters of error (defocus)
If aberration too strong the WFS spots will be If aberration too strong the WFS spots will be displaced outside their sub-aperturedisplaced outside their sub-aperture
Occurs on physically introduced aberrations onlyOccurs on physically introduced aberrations only Limits testing to resolution of lenslet and not stroke of Limits testing to resolution of lenslet and not stroke of
mirror.mirror.
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Dealing With Loss of WFS SpotsDealing With Loss of WFS SpotsSome aberrations are so strong that the computer cannot find all of the WFS spots
Using MATLAB we can correct for this by using an
extrapolation algorithm
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Characterization ProcessCharacterization Process
Control Loop closes and mirror corrects wave front
Before/After data analyzed
Place aberration into system
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ResultsResults
The group are continuing to work on data The group are continuing to work on data analysis algorithms and are implementing analysis algorithms and are implementing them in MATLABthem in MATLAB
Will be presented at Optics East 2005 Will be presented at Optics East 2005 SPIE Conference in BostonSPIE Conference in Boston11
The OCT / SLO set-up is under The OCT / SLO set-up is under constructionconstruction
1 Bimorph deformable mirror; an appropriate wavefront corrector for retinal imaging? –Sophie Laut, Steve Jones, Hyunkyu Park, David Horsley, Scot Olivier, John Werner
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Talk about the SLO systemTalk about the SLO system
Slide Courtesy of Sophie Laut,
UC Davis Medical Center
Bimorph DM
MEMS DM
OCT / SLO Schematic
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AcknowledgementsAcknowledgements This project is supported by the National Science Foundation Science and This project is supported by the National Science Foundation Science and
Technology Center for Adaptive Optics, managed by the University of Technology Center for Adaptive Optics, managed by the University of California at Santa Cruz under cooperative agreement No. AST - 9876783.California at Santa Cruz under cooperative agreement No. AST - 9876783.
Dr. Scot Olivier and Dr. Steven Jones at LLNLDr. Scot Olivier and Dr. Steven Jones at LLNL Dr. Sophie Laut and Prof. John Werner at UCDMCDr. Sophie Laut and Prof. John Werner at UCDMC Prof. David Horsley at UCDProf. David Horsley at UCD Everyone at the CfAO, LLNL, and UCD for a great internship experienceEveryone at the CfAO, LLNL, and UCD for a great internship experience