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UCL Optical Tweezers Group: Research

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We are involved in several lines of research at the interface of physics and the life sciences, involving the trapping and manipulation of microscopic objects with laser light (optical tweezers).  These include:

Contact Phil Jones for more about these and other research topics

Our work is funded by:

Leverhulme Trust

NanoSci

epsrc

royalsociety

nuffield

npl

UCL

These movies are also on our YouTube channel

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Optical trapping of microbubbles

Microscopic bubbles are used as a contrast agent in medical ultrasound scans.  The dynamics of the bubble under insonation are not well understood and so we will be using optical tweezers to trap and study the behaviour of microbubbles when irradiated with ultrasound.  Opposite is a movie of a microbubble being manipulated in the optical tweezers.

The microbubble in the trap is 4 microns in diameter and is held in a rapidly scanning circular trap.  The position of the trap can then be moved slowly to move the bubble with it.  We have performed a number of experiments to characterise in detail the optical trapping potential (see publications for more details).

 


Rotating optical traps for microfluidics

We are using optical tweezers to trap non-spherical microparticles which can then be rotated in a controlled manner to 'stir' the suspending fluid and studying the induced microscopic flow.  Watch a movie of a polystyrene double-bead rotating in the tweezers opposite.

The larger end of the double bead is 7 microns in diameter, and the smaller end 5 microns.  The trap is made by rapidly scanning the tweezer along the long axis of the double-bead while slowly rotating.

 


Optical trapping of carbon nanotubes

We have shown that bundles of carbon nanotubes can be trapped an manipulated in a scanning (time-averaged) optical tweezers.  as a part of this investigation we elucidated the role played in optical trappng of the surfactant that required to suspend the nanotubes in aqueous solution (see publications for more details).

This work is carried out in collaboration with Dr Onofrio MaragÚ from the  Laboratory for Nanoscience, IPCF-CNR, Messina.


Optical vortices

We have made calculations of the focusing of optical vortex beams in the limit of high numerical aperture, for example focusing by a microscope objective lens.  We have been able to investigate the range of vortex beam parameters that produce potentially useful intensity distributions around the focus, and also evaluate the effects of aberrations that can be introduced by, for example, focusing through a microscope cover slip.  We have also devised a method for experimentally generating arbitrary order (and fractional) polarization vortex beams (see publications for more details).


Optical nanofibres

In a new activity at UCL we will be using tapered optical nanofibres for evanescent wave binding of micro- and nanoparticles.  This project is a part of the NOIs Collaboration funded by EPSRC and Nanoscience Europe.

Opposite is a picture showing the intensities of the electric field components of the HE11 fibre mode in the region of a sub-optical wavelength fibre taper.  These calculations were made by Alex Dunning as a part of his Nuffield Foundation Undergraduate Research Bursary project.


nanofibres
The movie opposite shows 2 micron diameter polystyrene spheres that are trapped in the evanescent field of one of our tapered fibres  and propelled along it by radiation pressure.


Optical binding

We are invstigating the interaction of microscopic particles in evanescent fields that lead to optical binding - the spontaneous formation of arrays of particles held together by optical forces.  This can be seen in the movie opposite, where 1 micron diameter silica spheres form chains in the evanescent field that disintegrate when the laser is switched off and re-form when the laser is switched on again.




Our work is supported by EPSRC, Nanoscience Europe, the Royal Society, the Leverhulme Trust, the Nuffield Foundation, the UCL MAPS Faculty Research Fund, the National Physical Laboratory and the UCL Platform Technologies Initiative.


University College London - Department of Physics and Astronomy - Gower Street - London - WC1E 6BT - Telephone: +44 (0)20 7679 3422 - Copyright © 1999-2014 UCL


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