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Biological applications of optical tweezers (Experiment: Rubinsztein-Dunlop, Heckenberg)
The forces exerted by a focussed beam of laser light are strong enough to move small particles around in liquid media. Transparent particles are attracted towards the waist of the beam. In this way bacteria or cells or their components can be trapped and dragged around using laser beams of modest power.
We have already demonstrated trapping of bacteria and have collaborations in place to explore exciting applications in microbiology and anatomy. In one such application, selected bacteria will be separated from a known environment and moved anaerobically to a new location where they can be cultured and further studied. The technique can be also be used to optically manipulate the dendrites of nerve cells in culture with the objective of setting up specific connections in order to study the operations of such circuits. The ultimate aims include the construction of neural circuits for testing drugs and the development of implants for the repair of the damaged pathways.
Optical micromanipulation using donut beams (Rubinsztein-Dunlop, Heckenberg)
The laser micromanipulation group at the University of Queensland has pioneered the technique of using donut laser modes for optical manipulation of absorbing and reflecting particles, which vastly increases the range of potential applications. These beams are produced using specially designed computer generated holograms. We were the first laboratory to report the transfer of angular momentum from a laser beam, in which a trapped particle is caused to rotate in a striking confirmation of a classical prediction, with possible application to powering micromachines. The UQ theory group is currently developing a detailed theoretical model of the transfer of angular momentum. We will investigate the trapping of microscopic bubbles using this technique, with many applications in biology and medicine.
Development of an optical trap atomic force microscope (Rubinsztein-Dunlop, Heckenberg, UQ).
We have begun the development of an atomic force microscope where the stylus is a particle held in an optical trap. With a compliance orders of magnitude higher than a conventional cantilever, such an instrument will be suitable for imaging soft biological samples. Our preliminary experiments have already demonstrated detection of 40 nm amplitude Brownian motion of a trapped particle[28]
Rheological measurements in colloids using optically trapped sensors (Rubinsztein- Dunlop, Heckenberg in collaboration with Prof. Mackay - Stevens Institute of Technology, Nj. USA).
Rheological properties of silica particles suspended in a fluid will be performed by optically trapping a trace particle in a focussed laser beam and measuring a drag force required to move it through a colliodal suspension. In this way the effective viscosity of the suspension will be determined and the effects of nearby surfaces near which particles can form colloidal crystals will be studied, resolving a long standing problem of importance in engineering applications.
Laser dynamics and patterns (Heckenberg, Tang).
Our studies of nonlinear propagation, deterministic chaos, and pattern formation in lasers are well known internationally, and unique in Australia and have resulted in 17 publications. Our optically pumped far-infrared NH3 laser exhibits Lorenz-like chaos, and produces some of the best chaotic data available, allowing in depth testing of theory and analysis methods.
Our work is currently focussed on the effects of sudden parameter changes in chaotic systems and on means of controlling chaos by feedback. We are extending our work to the interactions of chaotic systems, such as synchronisation which has been proposed as the basis for secure communications. Other concerns are the interrelationship between chaotic and stochastic effects in real nonlinear systems.
Our work on spatial pattern formation in lasers is concentrated on the role of optical phase singularities in complex laser beam shapes. This work involves extensive collaboration with PTB, Braunschweig, Germany, particularly in the spatial dynamics of photorefractive oscillators. This work is important not only in its direct results and technological applications, but because state-of-the-art skills in laser dynamics and control are essential for the experiments in quantum optics. The program will focus on the temporal and spatial dynamics of lasers, and spatial dynamics of photorefractive oscillators
Laser Diagnostics (Rubinsztein-Dunlop, McIntyre).
The Laser Diagnostics group within the Physics Department at the University of Queensland is working on the development and application of advanced measurement techniques to high enthalpy flows, flames and plumes. The aim is to characterise such flows by the use of non-intrusive laser-based methods. Two tunable pulsed dye-laser systems and an intensified camera are available for spectroscopic applications while a pulsed Nd:YAG laser is used for interferometric methods. A number of techniques are being used for flow visualisation and for measurement of conditions such as velocity, density and temperature.
The group works closely with the Department of Mechanical Engineering who are developing the X series of superorbital expansion tubes, the world's fastest tunnels, which are capable of simulating re-entry conditions for both orbital and superorbital conditions. Holographic interferometry has been successfully applied to an air flow at 11km/s in the smallest tunnel X1. Future measurements are planned for this tunnel as well as the recently commissioned tunnel X2. Collaboration also exists with the CFD Group within Mechanical Engineering, the Chemistry Department as well as with groups in Canberra and overseas.