We are involved in several
research at the interface of physics and
the life sciences, involving the trapping and manipulation of
objects with laser light (optical tweezers). These include:
Contact Phil Jones
for more about
these and other research topics
Microscopic bubbles are used as a contrast agent
ultrasound scans. The dynamics of the bubble under insonation
understood and so we will be using optical tweezers to trap and study
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.
of the trap can then be moved slowly to move the bubble with
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
microparticles which can then be rotated in a controlled manner to
suspending fluid and studying the induced microscopic flow.
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
while slowly rotating.
Optical trapping of carbon nanotubes
We have shown that bundles of carbon nanotubes can
trapped an manipulated in a scanning (time-averaged) optical
tweezers. as a part of this investigation we elucidated the
played in optical trappng of the surfactant that required to suspend
the nanotubes in aqueous solution (see publications
for more details).
We have made calculations of the focusing of
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
devised a method for experimentally generating arbitrary order (and
fractional) polarization vortex beams (see publications
for more details).
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
Opposite is a picture
intensities of the electric field components of the HE11
fibre mode in the region of a sub-optical wavelength fibre
These calculations were made by Alex
Dunning as a part of his Nuffield Foundation
Undergraduate Research Bursary project.
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.
are investigating the interaction of microscopic particles in
fields that lead to optical binding - the spontaneous formation of
arrays of particles held together by optical forces. This can
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.
Optical fibre trap
are using a dual-beam optical fibre trap for optical trapping and
binding of microparticles, and also for investigating the mechanical
properties of soft dielectric materials by using it as an 'optical
stretcher'. The movie opposite shows a pair of 2 micron
diameter polystyrene spheres (visible by the scattered laser light)
trapped in the counter-propagating beams from a pair of single-mode