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]