Departmental Teaching Prize

Phil has won the Department of Physics and Astronmy's Departmental Teaching Prize for 2011.  In 2010-11 Phil was lecturing the course Lasers & Modern Optics (PHAS3443) for third and fourth year undergraduates.  The prize-giving ceremony will be held on Friday 28 October.  Earlier this year Phil also won the Mathematical and Physical Sciences (MAPS) Faculty Teaching Award.

New Group Members

Kelly Thorneycroft has joined the UCL Optical Tweezers Group for her MSci project.  Kelly is a fourth year undergraduate studying Natural Sciences and will be working on optical trapping and binding experiments and biophysical applications.

Electromagnetic and Light Scattering XIII

The latest conference in the series 'Electromagnetic and Light Scattering' (ELS XIII) is being held in Taormina, Sicily from 26-20 September.

Phil will be giving an invited talk about the UCL Optical Tweezers Group's research on Optical Trapping and Optical Binding Using Cylindrical Vector Beams.  The book of extended abstracts of all the conference presentations is published in a special issue of Atti della Accademia Peloritana dei Pericolanti Volume 89, Supplement No. 1 (2011).

Fano-Doppler Cooling paper

Our paper 'Fano-Doppler laser cooling of hybrid nanostructures' is now published in ACS Nano 5 7354-7361 (2011).

Laser cooling the center-of-mass motion of systems that exhibit Fano resonances is discussed. We find that cooling occurs for red or blue detuning of the laser frequency from resonance depending on the Fano factor associated with the resonance. The combination of the Doppler effect with the radiation cross-section quenching typical of quantum interference yields temperatures below the conventional Doppler limit. This scheme opens perspectives for controlling the motion of mesoscopic systems such as hybrid nanostructures at the quantum regime and the exploration of motional nonclassical states at the nanoscale.

Nuffield Bursary Update (3)

Throughout the course of her Nuffield Foundation project this summer Ewa Karczewska will be making updates of her progress on our blog.  Her final instalment is below.

Ewa writes: During the 8-week project with the UCL Optical Tweezers Group I have learnt a great deal about the laboratory work as well as the current experiments run in it, which focus on the evanescent field and the micro- and nano- structures trapping. I have also gain knowledge about the evanescent wave and the different optical fibre modes.
My research was focused on the thin fibre fabrication using the “heating and pulling”method. The light (λ = 1064nm) was coupled to the tapered fibre so that the evanescent field near the taper region was created. That field was then tested with the micro-sized spheres. When the field was strong enough and the surface of the fibre was smooth enough, the spheres were observed to move along the fibre along the direction of the light propagation.
Overall, I have managed to obtain an efficient method of obtaining thin (about 1.5μm in diameter) optical fibres using the “heating and pulling” method and observe the spheres of 2μm to move along the fibre once the laser light was coupled through it. When the laser light was coupled from both sides of the fibre I could move the spheres in two directions and also balanced the two beams so that the spheres stayed in place.
I have also investigated the behaviour of the micron-sized spheres when the polarisation of the trapping light of an optical tweezers was changed from linear to circular polarisation as well as from radial to azimuthal polarisation.
That project gave me a valuable experience and a great insight into the research work, which will be very useful in my future study for PhD.

From September Ewa will be studying for the third year of her degree as a year abroad in Toronto University.

Nuffield Bursary Update (2)

Throughout the course of her Nuffield Foundation project this summer Ewa Karczewska will be making updates of her progress on our blog.  Her first instalment is below.

Ewa writes: For the past two weeks, I have been investigating and making improvements to the flame brushing method, which then allowed me to obtain the fibres of less than 2µm in diameter. Therefore, after the study on how to make a good coupling between two optical fibres using the splices, the laser beam was coupled into the fibre and the nearby spheres of 2µm in diameter have been observed to move along the fibre in the direction of the light propagation. The spheres were observed to accelerate in the thinnest part of the fibre. When the laser beam was split into two and coupled to each end of the fibre, it was possible to move the spheres in both directions by changing the intensity of the light coupled to each end.  Also it has been observed that if the fibre breaks in the thin part and the laser beam is coupled into it, the spheres accelerate and shoot off from the broken end.

Above you can see a movie of 2µm diameter polystyreen microspheres propelled along a tapered optical fibre in the evanescent field of the guided laser beam.  More movie can be found on our YouTube Channel.

Jeremy Baumberg seminar

Professor Jeremy Baumberg (Cambridge University) will be giving the CMMP/LCN seminar on NanoAssembly on the kilometre scale for NanoPhotonics, Wed 22 Jun 11

Abstract: New photonic properties are produced in materials which are assembled from diverse combinations of metals, semiconductors and dielectrics that are periodically structured on the 100nm-scale, with a wealth of potential applications ranging from communications to bio-sensing. However producing such nanomaterials on the mass-scale is far from trivial as three-dimensional structures are very hard for traditional lithography, and self-assembly has to date been a lab-scale tricky process.

Here we concentrate on a new range of structural colour nanomaterials which can be mass produced as films on the kilometre scale. While most man-made (and natural) colours exploit dye absorption, there is strong interest in avoiding these carcinogenic and UV-bleached chemicals. Alternative structural colours are produced from periodic wavelength-scale-sized transparent components, and thus are benign, long-lived, and possess new optical features. We create polymer photonics crystals made of cross-linked polymer spheres dispersed in a soft elastomeric matrix, using a novel industrially-scalable shear-based nano-assembly. Simply tuning the size of the spheres changes the colour across the entire visible spectrum, while optimised shearing creates single-domain opal films. Stretching these unusual elastomeric photonic crystals breaks their traditional optical scattering selection rules, and enables many applications. We demonstrate a wide variety of new optical properties based on the resonant scattering phenomena.