research

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View movies of my experiments
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Department of Physics , University of Queensland

My PhD research:

My PhD thesis describes experiments with optical tweezers (or single-beam gradient optical trap), particularly about some of the mechanical effects light can have on

microscopic particles. Some of the things I looked at in this area were

Torque exerted on an absorbing particle by circularly polarized light
Torque exerted on an absorbing particle by a helical wavefront
Torques exerted on a birefringent material by polarized light
Driving the rotation of a microscopic "cog" with a spinning birefringent particle

Some other things I looked at were

Characterizing the strength of an optical tweezers trap by measuring its force constant
A scanning microscope/profilometer that uses an optically trapped sensor

My current research:

to be added

Movies of some of my experiments:

A clump of weakly absorbing polystyrene microspheres is trapped in a LG₀₃ donut beam, with a Dove prism placed in the beam path. The clump is at first slowly rotating in a clockwise direction. The Dove prism is then removed from the beam path, whereupon the clump reverses its direction and begins to rotate anti-clockwise. Click here to view the movie of the rotating clump .

A large black (absorbing) CuO particle approximately 5 mm across is radially trapped in a circularly polarized Gaussian laser beam, and slowly rotates due to transfer of spin angular momentum. Click here to view the movie of the large CuO particle .

A large, flat calcite crystal is aligned to the plane of polarization of the trapping beam. On rotation of a half-wave plate, the crystal slowly rotates around until it is again aligned with the plane of polarization. The change in beam polarization due to rotation of the half-wave plate occurs when the laser spot becomes brighter on the screen. Click here to view the movie of the alignment of the calcite crystal .

A calcite fragment rotates in elliptically polarized light. In this video, the rotation rate of the fragment is position dependent, but in circularly polarized light, the rotation rate would be constant. Click here to view the movie of the rotation of the calcite crystal .

An untrapped SiO₂ "cog'' circles a spinning calcite fragment, swept around by the motion of the fluid. Click here to view the movie of the circulating cog .

A SiO₂"cog'' and a calcite fragment are trapped in the same optical tweezers trap. The spinning calcite causes the "cog'' to rotate, at a much slower rate than the calcite.Click here to view the movie of the rotation of the cog and calcite crystal .

A SiO₂ "cog'' and a calcite fragment are trapped in two separate, steerable optical traps. As the spinning calcite fragment is brought near to the "cog'', the cog begins to rotate about its own axis. Click here to view the movie of the "turbine" .

last edited 30/3/99