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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

2020

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