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
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
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!
Optical Tweezers – Ray optics regimeOptical Tweezers – Ray optics regime
Light as a manipulator
•Particle:
•Index of refraction
> medium
•Diameter ~ 5x
wavelength to
100um
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
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
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!
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
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
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
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
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
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
+
+
+
+
-
+
+
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
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
Thank youThank you
Questions?
Shaun Bowman
Adaptive Optics Laboratory
University of Victoria
BC, Canada
Ph: 1 250 721 8624
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