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Optical Tweezing with Optical Tweezing with Adaptive OpticsAdaptive Optics
Canada France Germany - Young Photonic Researchers – Canada France Germany - Young Photonic Researchers – Munich, 2009Munich, 2009
Shaun Bowman
Supervisors - Dr. Colin Bradley, Dr. Rodolphe ConanAdaptive Optics Laboratory
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The Adaptive Optics Laboratory – University The Adaptive Optics Laboratory – University of Victoriaof Victoria
Lab facts:
•Founded 1998
•Dr. Colin Bradley, director
•2 post docs
•2 PhD candidates
•2 Masters students
•Co-op student / interns
•Contract professionals
Key equipment:
•Deformable mirrors: 1k,
64, 52, and 32 actuator
•Steer mirrors
•HASO Beam profiler
•Zygo interferometer
•Micro EDM mill
•Optics room
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The Adaptive Optics Laboratory – University The Adaptive Optics Laboratory – University of Victoriaof Victoria
Astronomy Collaboration
•European Space Agency
•ACURA
•University of California
•Thirty-Meter-Telescope Project
•NRC Hertzberg Institute of
Astrophysics
•University of Toronto
•Canada-France-Hawii
Telescope
•Caltech Astronomy
•... and a lot I don't know!
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Optical Tweezers – Ray optics regimeOptical Tweezers – Ray optics regime
Light as a manipulator
•Particle:
•Index of refraction
> medium
•Diameter ~ 5x
wavelength to
100um
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Optical Tweezers – Force applicator / Optical Tweezers – Force applicator / dynomometerdynomometer
Gauging and applying forces
•Overdamped 2nd order
system
•Brownian motion gives
Stochastic forcing function•=> Langevin equation
•=>Use power spectral density of
position to deduce stiffness
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Science Case for Optical TweezersScience Case for Optical Tweezers
Force extension
•Study of DNA uptake by
bacteria
•Observe uptake
•Measure stall-force
(7 – 40 pN typ.)
P. Johnson, Simon Fraser University, 2007
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Background on adaptive opticsBackground on adaptive optics
Adaptive Optics using deformable mirrors
•Wave description of light:
•A(x,y) => Amplitude
•ζ(x,y) => Phase
•Wave at trap = F( wave at aperture or deformable mirror)
The mirrors shape DIRECTLYdescribes the phase!
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Sensing phase, wavefront sensor – Sensing phase, wavefront sensor – the eyesthe eyes
Optical Tweezing
•Need phase for closed-loop
•Cant measure the phase
•Can measure focal position
•Tilted phase causes position shift
•Can measure SLOPE of the phase
•Shack-hartmann wavefront sensor
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Controlling phase, deformable mirrors – Controlling phase, deformable mirrors – the the handshands
Deformable mirrors
•Peizo:
•0.5 – 2 um stroke
•> 1khz bandwidth
•Voice coil
•5 – 100 um stroke
•> 400hz bandwidth
DM SHAPE = -0.5 x IN shape
IN OUT
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Closed loop control – Closed loop control – the brainsthe brains
Closed loop controllers
•Calibrate:
•Phase vs mirror
voltages
•Trap position vs
phase
•Invert
•Command new position
•Generate new phase reference
•Controller removes phase error
•Particle moves to new location
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Uvic Optical Tweezer ApperatusUvic Optical Tweezer Apperatus
Closed loop controllers
•Calibrate:
•Phase vs mirror
voltages
•Trap position vs
phase
•Invert
•Command new position
•Generate new phase reference
•Controller removes phase error
•Particle moves to new location
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Using particle position in wavefront Using particle position in wavefront controllercontroller
Command position in real units
•Particle detection by
symeteric-phase-only-matched-
filter (SPOMF) method
•Known Tip/Tilts applied to
relate wavefront and trap
position
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Using particle position in wavefront Using particle position in wavefront controllercontroller
Modified controller
[R] [W]t k(DM)Z-1
(WFS)Z-1
(PC)Z-1
DesiredTrap Location
Reconstruction Matrix
P
ReferenceWFS
Measurements
sr
+
ReconstructionWFS
Offsets
rr
+
+
+
+
-
+
+
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Using particle position in wavefront Using particle position in wavefront controllercontroller
Demonstration
•20 mW optical power at
objective
•15 um polystyrene bead
•30 x 30 um range of motion
•50 um max wavefront tilt
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Current workCurrent work
Calibration
•Stiffness as a function of trap
position
•2x2 Traps controlled by one
deformable mirror
totrap formingMicroscopeobjective
afterDMM andWFS beamsplitter
2x2 lenslets
collimating lens
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Thank youThank you
Questions?
Shaun Bowman
Adaptive Optics Laboratory
University of Victoria
BC, Canada
Ph: 1 250 721 8624