Transcript ShaunBowman

Optical Tweezing with Adaptive
Optics
Canada France Germany - Young Photonic Researchers – Munich, 2009
Shaun Bowman
Supervisors - Dr. Colin Bradley, Dr. Rodolphe Conan
Adaptive Optics Laboratory
The Adaptive Optics Laboratory – University of Victoria
Lab facts:
Key equipment:
•Founded 1998
•Deformable mirrors: 1k,
•Dr. Colin Bradley, director
64, 52, and 32 actuator
•2 post docs
•Steer mirrors
•2 PhD candidates
•HASO Beam profiler
•2 Masters students
•Zygo interferometer
•Co-op student / interns
•Micro EDM mill
•Contract professionals
•Optics room
The Adaptive Optics Laboratory – University of Victoria
Astronomy Collaboration
•European Space Agency
•University of Toronto
•ACURA
•Canada-France-Hawii
•University of California
Telescope
•Thirty-Meter-Telescope Project
•Caltech Astronomy
•NRC Hertzberg Institute of
•... and a lot I don't know!
Astrophysics
Optical Tweezers – Ray optics regime
Light as a manipulator
•Particle:
•Index of refraction
> medium
•Diameter ~ 5x
wavelength to
100um
Optical Tweezers – Force applicator / dynomometer
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 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 optics
Adaptive Optics using
deformable mirrors
•Wave description of light:
The mirrors shape
DIRECTLY
•ζ(x,y) => Phase
describes the phase!
•Wave at trap = F( wave at aperture or deformable mirror)
•A(x,y) => Amplitude
Sensing phase, wavefront sensor – the 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 – the hands
Deformable mirrors
IN
•Peizo:
•0.5 – 2 um stroke
•> 1khz bandwidth
•Voice coil
•5 – 100 um stroke
•> 400hz bandwidth
DM SHAPE = -0.5 x IN shape
OUT
Closed loop control – the brains
Closed loop controllers
•Calibrate:
•Command new position
•Phase vs mirror
•Generate new phase reference
voltages
•Controller removes phase error
•Trap position vs
•Particle moves to new location
phase
•Invert
Uvic Optical Tweezer Apperatus
Closed loop controllers
•Calibrate:
•Command new position
•Phase vs mirror
•Generate new phase reference
voltages
•Controller removes phase error
•Trap position vs
•Particle moves to new location
phase
•Invert
Using particle position in wavefront controller
Command position in real units
•Particle detection by
symeteric-phase-only-matchedfilter (SPOMF) method
•Known Tip/Tilts applied to
relate wavefront and trap
position
Using particle position in wavefront controller
Reconstruction
Desired
Matrix
Trap Location
+
+
+
[W]t
[R]
P
+
+
rr
Reconstruction
WFS
Offsets
-
sr
Reference
WFS
Measurements
Modified controller
+
(DM)
Z-1
k
+
(PC)
Z-1
(WFS)
Z-1
Using particle position in wavefront controller
Demonstration
•20 mW optical power at
objective
•15 um polystyrene bead
•30 x 30 um range of motion
•50 um max wavefront tilt
Current work
after
DMM and
WFS beamsplitter
to
trap forming
Microscope
objective
2x2 lenslets
Calibration
•Stiffness as a function of trap
position
•2x2 Traps controlled by one
deformable mirror
collimating
lens
Thank you
Questions?
Shaun Bowman
Adaptive Optics Laboratory
University of Victoria
BC, Canada
Ph: 1 250 721 8624
[email protected]