Thursday 28th of February 2019 at 6.30 to 7.45 pm
Napier 102 lecture theatre, 1st floor, Napier Building
University of Adelaide
Optical Tweezers ‘Demystified’
Assoc. Professor Bruce Wedding
University of South Australia
Since their invention 32 years ago, optical tweezers have become a powerful tool utilised in a wide variety of experiments in biology and physics. Optical tweezers use light to trap microscopic objects as small as 10 nm using radiation pressure from a focused laser beam. These trapped particles can then be manipulated and forces on the particles in the trap can be measured. The first designs of optical tweezers used high power lasers and expensive optical hardware. Recently however, simple and inexpensive apparatus for undergraduate laboratories can produce a single beam optical tweezer to trap micron-sized particles. Such a system in undergraduate laboratories and the resulting student engagement will be presented.
Interest in microfluidics is also a rapidly expanding area of research and the use of microchips as miniature chemical reactors, so called ‘Labs-on-a-Chip’ is increasingly common. Microfluidic channels are now complex and combine several functions on a single chip. Fluid flow details are important but relatively few experimental methods are available to probe the flow in a confined geometry. We can use optical trapping of a small dielectric particle to probe the fluid flow in microfluidic channels.
Rather than using the optical trap to position and release a particle for independent velocimetry measurement, we map the fluid flow by measuring the hydrodynamic force acting on a trapped particle. The flow rate of a dilute aqueous electrolyte flowing through a microchannel has been mapped using a small (1 µm diameter) silica particle. Such flow mapping is time efficient, reliable, and can be used in low-opacity suspensions flowing in microchannels of various geometries.
The Bronze Bragg medals and certificates will be presented at the lecture. The medal is awarded for highest achievement in Physics in 2018 in the SACE Stage 2 assessments, with certificates being for students who achieved a merit.
The presentation and lecture will be held in the Napier 102 Lecture Theatre, Napier Building, 1st floor, University of Adelaide, North Terrace, north from Pulteney St., at 6.30pm. Members of the public are warmly invited to attend. We are obliged for security reasons to keep the front door of the building attended, so please arrive before 6.30pm. Bookings are not available. The doors must be closed if all seats are taken.
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