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.

Faculty Teaching Award

Phil has won the Mathematical and Physical Sciences (MAPS) Faculty Teaching Award for 2011, shared with Prof Ted Johnson from the Department of Mathematics.  The MAPS Faculty comprises the departments of Chemistry, Earth Sciences, Mathematics, Natural Sciences, Physics & Astronomy, Science & Technology Studies, Space & Climate Physics, Statistical Science and the London Centre for Nanotechnology, and the award is made annually in recognition of outstanding provision of teaching within the faculty.  This year Phil was lecturing the course PHAS3443 Lasers & Modern Optics.

Nuffield Bursary Update

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.



Tapered glass optical fibre
with 2 micron polystyrene spheres 

 Ewa writes:  I have started this Nuffield Bursary project by studying the mechanical effect of evanescent optical fields on microscopic particles.  I have learned how to set up simple optical path using optical mirrors and lenses, and most importantly I have understood the basic ideas behind the use of the laser light for optical trapping.  Having been familiarised with the equipment in the laboratory and having been shown the experiment of array formation and optical binding in evanescent waves carried out by Marios Sergides, I have been using the heating and pulling method for making tapered optical fibres.  With this method I have produced several optical fibres of less than 2μm in diameter.  Using these fibres I will be trying to trap micron-sized spheres in the evanescent field, but first the efficiency of coupling and light transmission into the fibre must be improved.  To do this I have learned how to polish and connectorize optical fibres and measured the transmission efficiency.

UCL Science Centre Lecture

On Friday 10 June Phil is giving a lecture for the UCL Science Centre on Fifty Years of the Laser.  The UCL Science Centre organises a series of lectures aimed at 6th form students (and their teachers) on a wide variety of subjects.

Abstract: In this lecture we will review the history of the laser: from Einstein's early predictions about "amplified light", through their invention fifty years ago, when they were considered "a solution looking for a problem", to their widespread use today in applications such as telecommunications and holography. Along the way we will highlight some of the fascinating science and technology that the invention of the laser has made possible, and also showcase some of the current research from the UCL Department of Physics that uses lasers to trap and manipulate particles, to cool matter to nearly absolute zero or to probe the structure and function of biological molecules that are fundamental to life.

Lectures take place at 6.30pm in the Harrie Massey Lecture Theatre and last for 60 minutes, followed by a 30 minute question-and-answer session.

New group members

Ewa Karczewska is joining the UCL Optical Tweezers Group today for an eight week research project funded by the Nuffield Foundation.  The foundation provides research bursaries for undergraduate students considering a career in research to gain experience in a research lab over the summer vacation.  The Optical Twezeers Group has peviously hosted three Nuffield bursary students: Muddassar Rashid (2008), Alex Dunning (2009) and Radhika Patel (2010).

Ewa is a second year undergraduate student at UCL, studying for an MSci degree in Physics.  She will be contributing to a number of different projects presently running in the group, and making regular updates of her progress on this blog.

Andrei Rode visit and seminar

This week Prof Andrei Rode from the Laser Physics Centre of the Australian National University, Canberra is visiting.  While here he will also be giving an AMOP Physics seminar on Optical vortices: Trapping of particles and material processing.

Abstract: In physics and biology, manipulation of microscopic objects achieved remarkable precision and functionality using very small radiation pressure of light and dipole-induced gradient forces, so called optical tweezers.  Stable trapping of absorbing particles in air was not achieved till now due to the dominance of forces from thermal interaction of the laser-irradiated particle with the molecules of ambient gas.  We address this challenge by developing a touch-free optical trapping of particles suspended in air with optical vortices.  The ability to guide absorbing particles along the vortex core in a stable and controlled manner can be employed further for high-accuracy manipulation of particles in three dimensions.

We also developed a femtosecond vortex beam converter where polarization singularities are created when the beam propagates through a birefringent crystal, to produce sub-micron ring structures on the surface of fused silica and glass samples. We employ this technique to generate optical vortex as well as radially (TM) and azimuthally (TE) polarized fs-laser pulses for sub-µm structuring of glass samples.

Interaction of tightly focused multiple fs-pulses with transparent media allows one to imprint their local polarization pattern with sub-wavelength resolution, including the presence of the longitudinal component of electric field.  The materials’ response to the state of polarization of high intensity light fields has been used to map the complex vector structure in the focal volume of radially and azimuthally polarized fs-laser pulses.