Adaptive Optics for - Lick Observatorycfao.ucolick.org/pubs/presentations/eyedesign/08_AO...History...
Transcript of Adaptive Optics for - Lick Observatorycfao.ucolick.org/pubs/presentations/eyedesign/08_AO...History...
Adaptive Optics forVision Science
Nathan Doble
Class Outline• The Basic AO System
• Wavefront Sensors
• Deformable Mirror Technology• Control Loop Theory
• Current AO Systems in Use
• Typical System Performance
• Applications of AO
For a diffraction-limited system (i.e. one free of aberrations),The angular resolution α is given by:
α ≈ 1.22 λ / D
where λ is the wavelength and D is the aperture diameter.
Example: (λ = 550nm)
D = 10m (Keck telescope), α ≈ 0.013 arc secondsD = 8mm (dilated pupil), α ≈ 0.3 arc minutes
For Keck, α ≈ 0.5 arc seconds because of turbulence.For the eye, α ≈ 1 arc minute at best (smaller pupil).
History of Adaptive Optics
• Babcock 1953: suggested basic idea• Military work >> Maui CIS system, 168
actuators (1982)• ESO “Come-ON” system, 19 actuators (1990)• PUEO (1996), Hokupa’a curvature systems• Keck, Altair (Gemini N), NAOS (VLT)• Low cost AO >>> new applications• Eye, FSO Comms, Confocal microscopy
DeformableMirror
DichroicBeam Splitter
Telescope
ScienceCamera
WavefrontReconstructor
ActuatorControl
WavefrontSensor
Generic AO System
Two types of laser guide stars in usetoday: “Rayleigh” and “Sodium”
• Sodium guide stars: exciteatoms in “sodium layer” ataltitude of ~ 95 km
• Rayleigh guide stars:Rayleigh scattering from airmolecules sends light backinto telescope, h ~ 10 km
• Higher altitude of sodiumlayer is closer to samplingthe same turbulence that astar from “infinity” passesthrough Telescope
Turbulence
8-12 km
~ 95 km
Claire Max - CfAO lecture course
Adaptive optics allows telescopesto see through the turbulent atmosphere
Claire Max - CfAO lecture course
(Macintosh et al 1999 and Max et al 2000 in preparation)
Images of Neptune taken with infrared lightwith and without adaptive optics from the Keck telescope
Without AO With AO
R136
AO Off AO On
(Brandl et al, MPE Munich)
(K-band images (2.2µm), 3.6m telescope)
Key Research Issues inAstronomical AO
• Laser guide stars– Increase sky coverage
• Multi-conjugate adaptive optics– Increase field of view
• eXtreme AO (e.g. for planet detection)
• Next generation “overwhelmingly large”telescopes: up to 100m diameter
Claire Max - CfAO lecture course
Free Space Optics
AO needed to correct for effects of transmission medium
Replaces optical fiber for short point to point communications
Needs high temporal bandwidth, dynamic range and has to be
inexpensive Claire Max - CfAO lecture course
• Intracavity laser correction• Extracavity beam shaping• Correction of spherical aberration• Confocal microscopy• Ground-to-space optical communication• Laser materials processing• Submicron optical lithography• ‘Smart’ binoculars• Optical data storage• Optical instrument manufacture and alignment• Industrial inspection• VISION SCIENCE/OPHTHALMOLOGY
Other Applications of AO
Building blocks of AO systems:
• Wavefront Sensor
• Corrective Element
• Control loop
Wavefront Sensing• “Direct” in pupil plane- split pupil up into
subapertures in some way, then use intensity in eachsubaperture to deduce phase of wavefront. Sub-categories:– Slope sensing: Shack-Hartmann, lateral shear interferometer– Curvature sensing
• “Indirect” in focal plane - wavefront properties arededuced from whole-aperture intensity measurementsmade at or near the focal plane. Iterative methods -take a lot of time.– Image sharpening, multidither– Phase diversity
Claire Max - CfAO lecture course
Hartmann-Shack Wavefront Sensor(principle of operation)
Eye
Collimatedinput beam
Laserbeacon
Lensletarray
Hartmann-Shack Lenslet Array
∂W(x,y)∂ x
=D xF
∂ W(x,y)∂ y
=D yF
SLOPES
Liang - JOSA-A 1994
Raw data(CCD)
Wave aberration
Ideal optics JL's optics
contour lines = 0.15 mmDon Miller - Indiana
The Bausch and Lomb Zywave
Curvature wavefront sensing• F. Roddier, Applied Optics, 27, 1223- 1225, 1998
I+ − I−
I+ + I−
∝ ∇2φ − ∂φ∂r r
r δ R
Laplacian (curvature)
Normalderivative at
boundary
More intense Less intense
Claire Max - CfAO lecture course
Wavefront sensor lenslet shapes aredifferent for edge, middle of pupil
• Example: This is whatwavefront tilt (whichproduces imagemotion) looks like on acurvature wavefrontsensor– Constant I on inside– Excess I on right edge– Deficit on left edge
Lenslet array
Claire Max - CfAO lecture course
Curvature sensor signal forastigmatism
Claire Max - CfAO lecture course
Practical implementation ofcurvature sensing
• Use oscillating membrane mirror (2 kHz!) to vibrate rapidlybetween I+ and I- extrafocal positions
• Measure intensity in each subaperture with an “avalanchephotodiode” (only need one per subaperture!)– Detects individual photons, no read noise, QE ~ 60%– Can read out very fast with no noise penalty
More intense Less intense
Claire Max - CfAO lecture course
Advantages and disadvantages ofcurvature sensing
• Advantages:– Lower noise ⇒ can use fainter guide stars than S-H– Fast readout ⇒ can run AO system faster– Can adjust amplitude of membrane mirror excursion as
“seeing” conditions change. Affects sensitivity.– Well matched to bimorph deformable mirror (both solve
Laplace’s equation), so less computation.– Curvature systems appear to be less expensive.
• Disadvantages:– Avalanche photodiodes can fail if too much light falls on
them. They are bulky and expensive. Hard to use a largenumber of them.
Claire Max - CfAO lecture course
Detectors for wavefront sensing
• Shack-Hartmann: usually use CCDs (charge-coupleddevices), sizes up to 128 x 128 pixels– Sensitive to visible light (out to ~ 1 micron)
– Can have high quantum efficiency (up to 85%)
– Practical frame rates limited to a few kHz
– Read noise currently > 3 electrons per pixel per read
– New development: infrared detectors (more noise)
• Curvature: usually use avalanche photodiodes (1 pixel)– Sensitive to visible light
– Slightly lower quantum efficiency than CCDs
– NO NOISE
– Very fast
Claire Max - CfAO lecture course
Building blocks of AO systems:
• Wavefront Sensor
• Corrective Element
• Control loop
Types of Deformable Mirror (DMs)
• Conventional Piezoelectric DMs e.g. Xinetics, Thermotrex
• Bimorph
• Liquid Crystals e.g. Hamamatsu, Sony, Meadowlark
• Bulk micromachined e.g. OKO Technologies, Lucent
MEMS (Microelectromechanical Systems)
• Surface micromachined e.g. BMC, Iris AO
Continuous Faceplate - Xinetics
Claire Max - CfAO lecture course
Continuous face-sheet DM’s:Xinetics product line
Segmented deformable mirrors:
• William Herschel Telescope,UK: ThermoTrex 76element segmented mirror.
• Each square mirror ismounted on 3 piezos, each ofwhich has a strain gauge.
• Strain gauges provideindependent measure ofmovement, are used toreduce hysteresis to below1% (piezo actuators have~10% hysteresis).
Claire Max - CfAO lecture course
Bimorph mirrorsBimorph mirror are made
from a piezoelectric wafersandwiched between onecommon electrode and aseries of individual with anelectrode pattern betweenthe two wafers to controldeformation
Front and back surfaces areelectrically grounded.
When V is applied, one wafercontracts as the otherexpands, inducingcurvature
Claire Max - CfAO lecture course
Bimorph mirrors well matched tocurvature sensing AO systems
• Electrode pattern can beshaped to matchsubapertures in curvaturesensor
• Mirror shape W(x,y) obeysPoisson Equation
Claire Max - CfAO lecture course
Liquid Crystal Spatial Light ModulatorsHamamatsu Meadowlark
Lucent Technologies
d1
d2σ V_+D
• mirror deforms in both directions inresponse to voltage commands (pressurechanges sign with voltage)
• greater mirror deformation: higherelectrostatic pressure can be achievedwith the same voltage as ordinarymembrane mirrors
• more stroke at all spatial frequencies dueto higher electrostatic pressure. Enablescorrection of higher order Zernike modes.
BulkMicromachined MEMSOKO Technologies - G Vdovin
Single membrane - 37 actuators
6 microns of pure defocus
~1.2 microns on correction of higher
order modes
BostonMicroMachines/BostonUniversity MEMS DM
Electrostaticallyactuateddiaphragm
Attachmentpost
Membranemirror
Continuous mirror
Segmented mirrors (piston)
• Fabrication: Siliconmicromachining(structural silicon andsacrificial oxide)
• Actuation:Electrostatic parallelplates
Piecewise Continuous
A rigid, single-crystal-silicon mirror is assembled onto a surface-micromachined parallel-plateactuator. The actuator is elevated 60 microns above the surface of the substrate because ofbending caused by residual stresses in the nickel-polysilicon bimorph flexure.
Iris AO - Segmented piston tip/tilt array
SPECIFICATION XINETICS OKOTECH
BMCMEMS
HAMAMATSULC-SLM
LUCENTTECH
IRISAO
Active area (mm) φ = 75 φ = 15 3.3x3.3 20x20 φ = 10 φ = 7No. of actuators 97 37 12x12 480x480 1024 89
Surface type Continuous Membrane ContinuousPiecewise
Pure Piston Membrane SegmentedPTT
Stroke(wavefront)
± 4 µm ± 0.7 µm ± 2 µm 10's µmsPhase Wrap
±10 µm >15 µm
Response speed 4kHz 0.5kHz 3.5 kHz 13 Hz 250HzOperating voltage 100V 255V 220V 5V 200V 100V% of populationcorrected (Z4 = 0,
6.8mm pupil)75 10 20 100 95 100
Current and Near Future DM Technologies
Requirements of a deformableRequirements of a deformablemirror for vision AOmirror for vision AO
Temporal Bandwidth 1-3Hz closed loop⇒ 30 Hz samplingMirror Stroke(6.8 mm pupil)
10+µm (defocus corrected)6+µm (defocus and astigmatism)
Flatness <30nm rms.Actuator Coupling 10-15%Reflectivity >90% (400-900nm)No. of actuators orsegments across thepupil
13x13 Continuous faceplate11x11 Segmented PTT60x60 Segmented Piston only
Size (diameter) 4-8mm i.e. comparable to pupil size
Brief History of Vision AO
First use of a HS-WFS for the eye was by Liang 1994
In 1997, Liang et al. (JOSA-A) used a 37 channel Xinetics DMoperated open loop with the HS-WFS.
In vivo classification of the three cone classes (Roorda Nature1999)
First active correction of a laser scanning ophthalmoscope (SLO)by Dreher (Appl Opt 1989).
Confocal laser scanning ophthalmoscope with AO (Roorda OptEx 2002)
GROUP TYPE DM WFS PERFORMANCE REFERENCERochester(Williams)
Conventional 97 ch Xinetics
37 ch MEMS
HS
HS
<0.1 µm rms, φ = 6.8 mm
0.17 µm rms, φ = 6.8 mm
Hofer Opt Ex 2001
Doble Opt Let 2002Houston(Roorda)
ConfocalSLO
37 ch Xinetics HS ~0.1µm rms, φ = 7 mm Roorda Opt Ex 2001
Indiana(Miller)
Coherencegated
37 ch Xinetics HS Coming online
Murcia(Artal)
Conventional 37 ch Membrane
LC-SLM
HS
HS
0.12 µm rms, φ = 4.3 mm
0.1 µm rms, φ = 4.7 mm
Fernandez Opt Let2001Martin JOSA-A 1998
Imperial Col(Dainty)
Conventional 37 ch Membraneplus tilt mirrors
HS >0.1µm rms, φ = 4.8 mm Monroe 3rd Int Confon AO for Ind + Med
San Diego(Bartsch)
Conventional 19 ch Membrane HS >0.5 µm P-V, φ = 8 mm Zhu App Opt 1999
LLNL (UCD)(Olivier)
Conventional LC-SLM HS In initial system testing N/A
Chengdu,(Jiang)
Conventional In house 52 chDM
HS 0.18µm rms, φ = ?? Zhang 3rd Int Confon AO for Ind + Med
Paris(Gargasson)
Conventional 13 act. mirror HS φ = 7mm Glanc Sub to Appl.Opt
Vision AO systems - global
Why do we need AO for the eye?SPATIAL Cornea ⇒ anterior surface
⇒ posterior surfaceCrystalline lens
Contribution of each refracting surface to wavefrontaberrations depends on the refractive index differencebetween two optical media.
Cornea (Anterior > Posterior) > Lens∆n = 0.376 ∆n = 0.05
TEMPORAL AccommodationEye / Head movements
Factors influencing magnitude ofocular aberrations…...
• Pupil Size•Accommodation•Eye ‘instability’•Age•Eye disease
1 mm 2 mm 3 mm 4 mm
5 mm 6 mm 7 mm
Point Spread Function vs. Pupil SizePerfect Eye
pupil images
followed by
psfs for changing pupil size
1 mm 2 mm 3 mm 4 mm
5 mm 6 mm 7 mm
Point Spread Function vs. Pupil SizeTypical Eye
Effect of pupil diameter on the WA
7 mm
3 mm
7 mm
5.8 mm
4.6 mm
(Artal & Navarro, JOSAA, 1994)
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2
Accommodation (diopters)
Seid
el a
berr
atio
n co
effic
ient
(mic
rons
)
ComaAstigmatismSpherical aberration
SC HH PA
Aberrations change with accommodation
4.7mm pupil
⇒ Higher order correction for near viewing not appropriate for distanceviewing and vice versa
HH viewing distant target, 5.8 mm pupil, 550 nm monochromatic light Videos represent wave aberration measurements taken at 25.6 Hz during a 5 second interval.
Short Term Instability Wave Aberration Point Spread Function
Aberrations from the eye is not static. Dynamic range of eye’s wave aberrationsrequires a closed loop bandwidth 1~2 Hz to correct the temporal fluctuation.
Keratoconics suffer from abnormally highamounts of aberration.
Wave Aberration PointspreadFunction Retinal Image
1 deg5.7 mm pupil
Keratoconus
TypicalSubject
The Rochester 2nd generationadaptive optics system
Hot mirror
SLDλ = 820 nm
Lenslet array
CCDHartmann-Shackwavefront sensor
Xinetics Deformablemirror
Hot mirror
SLDλ = 820 nm
Lenslet array
CCDHartmann-Shackwavefront sensor
Xinetics Deformablemirror
CCD
Retinal imageCold mirror
550 nm filter
Kryptonflash lamp
Retinal imaging
System Layout
AO System Parameters
Correction Device 97 channel Xinetics DM, ±4µm wavefront stroke
Imaging Source Krypton flashlamp centered at 550nm, 4msec exposure duration
Science Camera Cooled back-illuminated CCD (Roper Scientific: MicroMAX)512×512, 24µm square pixels, max. frame rate of 3Hz
Wavefront Sensor Hartmann-Shack, 17x17 lenslets, f=24mm, φ = 0.4mm
WFS Source Superluminescent diode at 810nm, 20nm bandwidth
WFS Camera Cooled frame transfer CCD (Roper Scientific: PentaMAX)512×512, 15µm square pixels, max. frame rate of 30Hz
Bandwidth ~1Hz closed loop, 30 Hz sampling, 10th order Zernike correction
RMS after AO <0.1 microns for a 6.8mm pupil.
Important considerationsfor wavefront sensor
design
Corneal Reflection
Cornea > Retina20-20000
3 possible solutions!
• Pinhole
• Use of polarized light
• Off axis entry beam
Removing the corneal reflection
Eye
Collimatedinput beam
Laserbeacon
Lensletarray
PINHOLE
POLARIZEDINPUT BEAM
OFF AXISBEAM
Image Speckle
Rapidly scan beacon across retina (Hofer 1999)( complex )
Let retinal motion decorrelate speckle
(a) Laser, polarized > 500 msec
(b) Laser, unpolarized > 200 msec
(C) SLD, unpolarized > 30-50 msec
Retinal Reflectivity
400 450 500 550 600 650 700 750 800 85010-1
100
101
102
Wavelength in nm
PerifoveaFovea
WFS
SLD chosen wavelength is~800nm. Good reflectivity. Shortcoherence length, minimizesspeckle. Shorter depth of retinapenetrated.
Imaging Wavelength
Chosen to be at 550nm,corresponds to the average peaksensitivity of the L and M conepigment.
How much light can safely enter the eye?
Wavelength Exposure Max Perm Exposure
0.4 - 0.7 18x10-6 to 10 sec 0.0006927 t3/4 joules
0.0006927 t3/4 10 2 (λ - 0.7) joules0.7 - 1.05 18x10-6 to 103 sec
ANSI, American National Standard for the Safe Use of Lasers, ANSI Z136.1-1993,(Laser Institute of America, Orlando, FL, 1993).
Eg 1: What is the maximum power"safely" allowed for a 1/4 secexposure?
Ans: 1 mW for λ < 0.7µm1.4 mW for λ = 0.78 µm
Eg 2: How far below the MPE is a typical Hartmann sensor for the eye?(10 µ Watts, 200 msec, λ = 0.63 µ m)
Ans: Energy of HS = 2 µjoulesMPE= 207 µjoules
Configuration of 97 channel DM
Clear aperture77.4 mm (7.24 mm)
Pupil size for AO6.8 mm
Pupil size for retinal imaging6 mm
PMN Actuators7 mm (0.672 mm) spacing4 µm stroke
Configuration of 221 lenslet array and 97 channel DM
Clear aperture77.4 mm (7.24 mm)
Pupil size for AO6.8 mm
Pupil size for retinal imaging6 mm
Actuators7 mm (0.672 mm) spacing4 µm stroke
Lenslets (221 of 17×17)0.4 mm (0.384 mm) spacing24 mm focal length
Hartmann-Shack spot array
Hartmann spot on CCD Centroid boxes
Wavefront sensing --- Centroid algorithm
Local tiltedwave front lenslet
Focalplane
∆kθk
f
skx =∆xf
∆y =
∂ϕ (x, y)∂yk
∫∫dxdy
k∫∫
=
P(j∑
i∑ i. j)yij
P(i, j)j∑
i∑
∆x =
∂ϕ(x, y)∂x
k∫∫
dxdyk∫∫
=
P(j=1
j= J
∑i=1
i= I
∑ i.j) xij
P(i, j)j=1
j= J
∑i=1
i= I
∑
sky =∆yf
Local slope
Spot centroid
Real spotcentroid
Ideal spotcentroid
Initialcentroid box
Lastcentroid box
Wavefront sensing --- Centroid iteration algorithm
Shrinkingcentroid box
Advantage: reducing noise effect and improving the precision for centroid
estimatedcentroid
realcentroid
realcentroid
estimatedcentroid
Shrinkingcentroid box
Wavefront Control – Reconstruction of the wavefront todetermine the actuator commands
Wavefront correcting----Direct slope control algorithm
Slope vectorResidual
WavefrontReconstruction
Voltage vectorZ+ E+
Slope vector Voltage vectorD+
Direct Slope Control – Using wavefront slope as controlobjective.
Benefit of direct slope control algorithm
• Fast
• Without wavefront reconstruction error
• Tolerance to small misalignment betweenwavefront sensor and DM
Direct slope control algorithm
Flow chart to generate influence function matrix
Flatten DM
Add V1to Actuator i
Actuator i=1
Average 10 frames wavefront slope data in Si1
Add V2 to Actuator i
Average 10 frames wavefront slope data in Si2
Si=(Si2- Si1 )/(V2-V1)
i>97No
i=i+1
YesD=[S1, S2, ……, Si, ……S97]442x97
End
Start
D =
s(1,1)x s(2,1)x L s(N ,1) xs(1, 2)x s(2,1)x L s(N ,2) x
M M M M
s(1,M) x s(2,M) x L s(N,M)xs(1,1) y s(2,1)y L s(N ,1) ys(1,2)y s(2,2)y L s(N ,2) y
M M M M
s(1,M) y s(2,M) y L s(N,M)y
2M ×N
M: total number of lenslets (221)N: total number of actuators (97)
Direct slope control algorithm
S =
s1xs2xM
sM x
s1ys2 yM
sM y
V =
V1V2M
VN
V = D+Svoltage forupdata actuators slope influence function slope from WFS
M: total number of lenslets (221)N: total number of actuators (97)
D =
s(1,1)x s(2,1)x L s(N ,1) xs(1, 2)x s(2,1)x L s(N ,2) x
M M M M
s(1,M) x s(2,M) x L s(N,M)xs(1,1) y s(2,1)y L s(N ,1) ys(1,2)y s(2,2)y L s(N ,2) y
M M M M
s(1,M) y s(2,M) y L s(N,M)y
2M ×N
TEMPORAL
CHARACTERISTICS
Sampling period T(33ms):
VExposure Readout Centroid
Voltage Updata mirror
Timing sequence in AO system
Time delay τ=2TV
2TT 3T 4T
Exposure Readout Centroid
Voltage Updata mirror
Time
1 − e−Ts
Tse−τs C(s) 1
Eye aberration DMResidualaberration
y(s)r(s)e(s)
1 − e−Ts
Tse−τs
Eye aberration Residual aberration
y(s)
r(s)e(s) kcs
Feedback control: V((n)T)= V((n-1)T)+0.3Voltage((n)T)
C(s)=kc/s
-
-
+
+
+
Sensornoise
n(s)
+
Sensornoise
n(s)
AO system with transfer function model
From this model, the bandwidth is 0.9Hz@ 20Hz sampling rate, and 1.1Hz @30Hz sampling rate.
100.01
0.1
1
10
100
0.1 1
Static compensation
Dynamiccompensation
Average wavefront power spectrum
System performance---Dynamic compensation
Rat
io c
lose
d-lo
op p
ower
/ op
en-lo
op p
ower
model
data
0.01
0.1
1
10
0.1 1 100.01
0.1
1
10
0.1 1 10Temporal frequency (Hz) Temporal frequency (Hz)
Wavefront disturbance rejection
Model: 0.9Hz, Experimental data: 0.85Hz
6 subjects, 20Hz frame rate
00.10.20.30.40.50.60.70.80.91
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33
Frame number
Rm
s wav
efro
nt er
ror
(6.8
mm
pup
il)mydriacyl, 67msec exposure, 30% gain, no binning with CCD, 8 Hz frame rate
Evolution of the correction - Pupil and PSF planes
GYY, 6.8 mm pupil, 550 nm
AO Retinal Imaging at a Microscopic Spatial Scale
Courtesy Austin Roorda
Cone classing experiments
Courtesy Austin Roorda, Heidi Hofer
JC, 1.25 deg temporal
%L = 66 ± 4
JW, 1 deg temporal
%L = 80
BS, 1.25 deg nasal
%L = 94 ± 3
MD, 1.25 deg nasal
%L = 60 ± 3
AP, 1.25 deg nasal
%L = 51 ± 3
YY, 1 deg nasal-superior
%L = 51 ± 5
1
1.5
2
2.5
3
3.5
0 4 8 12 16 20 24 28 32V
isual
ben
efit
Spatial frequency (c/deg)
5.7 mm pupil
0
0.2
0.4
0.6
0.8
1
0 10 20 30 40 50 60
Mod
ulat
ion
tran
sfer
Spatial frequency (c/deg)
all monochromatic aberrations corrected
only defocus and astigmatism corrected
Visual Benefit of correctinghigher order aberrations
Mean of 109 subjects
5.7 mm pupil
0
5
1 0
1 5
2 0
2 5
3 0
3 5
4 0
0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4
Visual Benefit
Num
ber o
f Sub
ject
s Keratoconics
16 c/deg5.7 mm pupil
Keratoconics could especially benefitfrom correcting higher order aberrations
Conventional refraction Adaptive optics
The Rush Rhees tower viewed from half a mile away in broadband light with a large (6.8mm) pupil.
Improvement in average Strehl RatioImprovement in average Strehl Ratiowith dynamic AO correctionwith dynamic AO correction
0
0.1
0.2
0.3
0.4
0.5
No AOcorrection
Staticcorrection
Dynamiccorrection
6 subjects6 mm pupil size
550 nm
Stre
hl R
atio
Heidi Hofer
Increase in the power at the coneIncrease in the power at the conespatial frequenciesspatial frequencies
2
11.11.21.31.41.51.61.71.81.9
Spatial Frequency (c/deg)10 20 30 40 50 60 70 80 90 100 110 1200
Rat
io o
f Im
age P
ower
cones
Heidi Hofer
Ratio for a dynamic to static correction
• 512 X 480 pixels• 30 frames per second (uncompressed digital video)• 660 nm wavelength• 37-channel Xinetics deformable mirror• Shack-Hartmann wavefront sensor• Continuous zoom from 1 X 1 to 2.5 X 2.5 deg field
AOSLO Schematic
Axial Sectioning Capability
Vision AO system for UCDavis Medical Center
Laboratory systemdeveloped at LLNL, inconsultation withUniversity of Rochester,for use at UC DavisMedical Center for clinicalinvestigation of the limitsof human visual acuity
• Demonstrates high-accuracy, small, inexpensive Liquid CrystalSpatial Light Modulator wavefront corrector technology
THE END
The Whole Eye is Better than the Sum of Its Parts
Cornea Internal Optics Whole Eye
Artal, Guirao, Berrio, and Williams, Journal of Vision,1, 2001
0
0.5
1
1.5
2
2.5
3
3.5
4R
MS
wav
efro
nt er
ror (
µm)
Z20 Z 2
-2 Z22 Z 3
-1 Z31 Z 3
-3 Z33 Z4
0 Z42 Z 4
-2 Z44 Z 4
-4 Z51 Z 5
-1Z53 Z 5
-3 Z55 Z 5
-5
80%
2.7%10%
1.8%0.9%
0.9%0.7%
1.6%
0
0.1
0.2
0.3
0.4
0.5
Z 2-2 Z2
2 Z 3-1 Z3
1 Z 3-3 Z3
3 Z40 Z4
2 Z 4-2 Z4
4 Z 4-4 Z5
1 Z 5-1 Z5
3 Z 5-3 Z5
5 Z 5-5
Mean of 109 subjects5.7 mm pupil
Population Statistics of the Eye’s Wave Aberration(Zernike Analysis)
DefocusAstigmatism
Coma SphericalAberration Porter - JOSAA 2001
Inter-subject variability in MTF(Castejón-Mochón et al., Vision Res., 2002)
MTF
Perfect Eye
Planar wavefront
Spherical wavefront
Aberrated Eye
Aberrated wavefront
Wavefront Errors of the Eye:
Ordinary AO vs. MCAO: Computer Simulation
J band (1.2µm) , 1’ FOV Ø, “Gemini like” MCAO, stars magnified 10xClaire Max - CfAO lecture course
1.2µm Claire Max - CfAO lecture course
Wavefront Stroke - 5.7mm Pupil
Optimized Defocus Optimized defocus and corrected astigmatism (0.25D)
Data from Jason Porter, U of R
.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0%
80.0%
90.0%
100.0%
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 More
P-V in microns
.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0%
80.0%
90.0%
100.0%
P-V in microns
Wavefront Stroke - Wavefront Stroke - 6.8mm Pupil6.8mm Pupil
Populat ion_PV_Stroke
0
1009594
75
54
28
0
10
20
30
40
50
60
70
80
0 4 8 12 16 20 24 28 32
PV (microns)
Zeroed defocus
Data: Hauwei Zhao, U of Indiana 70 subjects - left eye shown
Populat ion_PV_Stroke
0
10010010091
81
43
0
10
20
30
40
50
60
70
80
0 4 8 12 16 20 24 28 32
PV (microns)
Zeroed defocus andastigmatism
Influence functions for XineticsDM
• Push on four actuators, measure deflectionwith an optical interferometer
Claire Max - CfAO lecture course
Shack-Hartmann wavefrontsensor concept - measure
subaperture tiltsf
CCD CCD
Claire Max - CfAO lecture course
Raw data(CCD)
Wave aberration
Eye lid wide open Normal position
Simulation of curvature sensorresponse
Wavefront: pure tilt Curvature sensor signal
G. ChananClaire Max - CfAO lecture course
Measurement error fromcurvature sensing
• Error of a single set of measurements is determined byphoton statistics, since detector has no noise:
where d = subaperture diameter and Nph is no. of photons persubaperture per sample period
• Error propagation when the wavefront is reconstructednumerically using a computer scales poorly with no. ofsubapertures N:– (Error)curvature ∝ N, whereas (Error)Shack-Hartmann ∝ log N
σcs2 = π 2 1
Nph
d
r0
2
Claire Max - CfAO lecture course
Wavefront Sensing - Laser Beacon
� Superluminescent diode (SLD) : 810nm wavelength, 20nmspectral spread
� Coherence properties : 30 micron, less speckle in wavefrontsensor spots
� SLD power: ~ 5µW
� Suppliers – Volga, Superlum, (Anritsu?) etc
Towards low cost AOsystems for clinicalresearch settings
Retinal Imaging with BMCRetinal Imaging with BMCMEMSMEMS
Without AO With MEMS AO
6 registered images for each caseFOV ~ 0.250 , 75µm on the retina