At the start of the new academic year we are welcoming several new members to the Optical Tweezers Group. Chris Richards and Tom Smart are new PhD students who will both be working on the project Exploring Stochastic Thermodynamics with Optical Traps. Chris is a UCL Physics graduate, and worked in the group last year for his MSci project. Tom comes to us from Leeds University via IoP publishing where he worked for 12 months in the editorial office.
Alessandro Magazzu has also joined us as a visiting student for one month under the EU COST Action MP1205 on Optofluidics. Alessandro is in the second year of his PhD at Università degli Studi di Messina, Sicily, and is supervised by Dr Onofrio Marago at the NanoSoft Lab, IPCF-CNR.
Finally Adam Plowman is joining us for his MSci project to investigate the dynamics of artificial micoswimmers.
The article on Optical Tweezers has now been published in the Taylor & Francis Encyclopedia of Optical Engineering.
From the abstract: Optical tweezers are devices that use a single, strongly focused laser
beam for the remote, non-contact trapping and manipulation of
microscopic objects. Since the first demonstration of optical tweezers
in 1986, they have become commonly used across physics, chemistry, and
biology for experiments as diverse as measuring the step size of motor
proteins to a demonstration of fluctuations in entropy production in
microscopic systems. In this entry, the mechanism behind optical
tweezers is introduced, followed by a discussion of practical aspects in
the use of optical tweezers, such as data collection and analysis for
quantitative measurements, and the use of holographic optical traps.
Also, a review of one of the many applications of optical tweezers is
presented, namely, the optical trapping of nanoparticles and
nanostructures and their use for imaging and force sensing.
Congratulations to former Optical Tweezers PhD student Dr Susan Skelton who has won the Carey Foster Prize for 2013 for her thesis Applications of
cylindrical vector beams to optical micromanipulation The Carey Foster Prize is awarded annually for outstanding postgraduate research in Atomic, Molecular, Optical and Positron Physics to a PhD student who has submitted their thesis in the past year.
Susan gained her PhD in February 2013, and is presently a postdoctoral research associate at the Laboratory
for Scientific Instrumentation and Engineering (LaSIE) at the
University of Osaka, Japan.
As part of the NPL/UCL/Oxford microbubble trapping collaborative project a paper Theoretical characterisation of the radial and translational motion of coated microbubbles under acoustic excitation has been published as C. J. Harfield et al, J. Phys.: Conf. Ser 457 012001 (2013).
From the abstract: Ultrasound contrast agents, in the form of coated microbubbles, are a
powerful tool in current diagnostic imaging. Given their sensitive
dynamic response they also have the potential to be used for
quantitative measurements of the properties of the surrounding tissue (e.g.
percentage perfusion or blood pressure). For this potential to be
realised, however, the theoretical descriptions of bubble behaviour, in
particular the constitutive equations for the microbubble shell, need to
be improved and a method needs to be developed for the accurate
characterisation of individual bubbles. In this paper the first steps
are taken towards deriving a complete model for the coupled radial and
translational motion of a coated bubble. It is then shown that with this
model the bubble can be characterised by a unique set of parameters
describing the bubble shell corresponding to its viscous and elastic
response. This uniqueness will enable the model to be used to interpret
experimental data and quantify these parameters for which accurate
values are currently lacking but which are critical to predicting bubble
response and hence enabling advanced diagnostic applications.
We are pleased to welcome Prof Jixiong Pu (Huaqiao University) to the group as a distinguished visiting scholar. Prof Pu is Professor of Physics and Dean of the
College of Information Science and Engineering, Huaqiao University.
He has been awarded a visiting scholarship to come to UCL and will be staying with us from 25 July - 08 September 2013, His research
interests include the generation of partially coherent light beams and
their focusing and propagation, vortex beams, tight focusing of
stochastic electromagnetic beams, applications of surface plasmon
polaritons (SPP), and optical manipulation
UCL Physics students Adam & Nat have entered their idea Konnect - The smart lecture experience into the JISC Summer of Student Innovation competition.
Learning works best with participation. However, lectures are typically highly passive experiences. For the students, lectures are more akin to watching a performance than expanding their knowledge and understanding of a particular topic. This is especially true for students in their first year of university who have become accustomed to relatively small classes at school and college.
We propose a platform that provides a real time connection between students and their lecturer. We aim to make the lecture environment one that promotes engagement; students will start to question their understanding for themselves. Essentially, our platform is comprised of a website, which acts as the hub of the service, and a smart phone app for students. Using these, a connection can be formed between a lecturer and his/her students.
Vote for Adam & Nat's idea with the JISC Elevator Vote button opposite.
This year we have had two MSci students working in the group for their final year projects. Chris Richards used Mie scattering theory to calculate optical forces experiences by microscopic particles in optical trapping experiments. In particular he was interested in finding the range of parameters for which an optical pulling force or 'tractor beam' was possible. By finding the fields scattered by a dielectric sphere and evaluating the Maxwell Stress Tensor to find the distribution of optical stress over a sphere he was able to determine the combination of beam and particle properties that would lead to the strongest 'backward' directed scattering force. Above you can see some of Chris' calculated stress distributions on the sphere surface in the forward- and backward scattering directions.
Zhi Hao Wong also worked with us to investigate the optical properties of metallic nanoparticles. Opposite you can see the calculated extinction spectra for gold and silver spherical nanoparticles as a function of size and optical wavelength which clearly show the enhancement of optical scattering arising from their plasmonic properties. Zhi Hao then went on to investigate how these properties could be used to control the dynamics of metallic nanoparticles in optical fields.
More MSci projects will be available for Physics and Natural Science students in the year 2013-14. Contact Dr Phil Jones for details of available projects.
From the abstract: Optical tweezers are devices that use a single, strongly focused laser
beam for the remote, non-contact trapping and manipulation of
microscopic objects. Since the first demonstration of optical tweezers
in 1986, they have become commonly used across physics, chemistry, and
biology for experiments as diverse as measuring the step size of motor
proteins to a demonstration of fluctuations in entropy production in
microscopic systems. In this entry, the mechanism behind optical
tweezers is introduced, followed by a discussion of practical aspects in
the use of optical tweezers, such as data collection and analysis for
quantitative measurements, and the use of holographic optical traps.
Also, a review of one of the many applications of optical tweezers is
presented, namely, the optical trapping of nanoparticles and
nanostructures and their use for imaging and force sensing.
This year we have had two MSci students working in the group for their final year projects. Chris Richards used Mie scattering theory to calculate optical forces experiences by microscopic particles in optical trapping experiments. In particular he was interested in finding the range of parameters for which an optical pulling force or 'tractor beam' was possible. By finding the fields scattered by a dielectric sphere and evaluating the Maxwell Stress Tensor to find the distribution of optical stress over a sphere he was able to determine the combination of beam and particle properties that would lead to the strongest 'backward' directed scattering force. Above you can see some of Chris' calculated stress distributions on the sphere surface in the forward- and backward scattering directions.
