Tuesday, 8 April 2014

Paper in J Phys: Conf Ser

A paper on laser vibrometer characterization of the ultrasonic coupling into the microfluidic chips used in the NPL/UCL microbubble trapping project as presented at the 12th Anglo-French Physical Acoustics Conference (AFPAC2013) 16-18 Jan 2013, has been published as C. Fury et al, Laser vibrometry characterisation of a microfluidic lab-on-a-chip device: a preliminary investigation J Phys: Conf Ser 498 012002 (2014).

From the abstract: Since their original inception as ultrasound contrast agents, potential applications of microbubbles have evolved to encompass molecular imaging and targeted drug delivery. As these areas develop, so does the need to understand the mechanisms behind the interaction of microbubbles both with biological tissue and with other microbubbles. There is therefore a metrological requirement to develop a controlled environment in which to study these processes. Presented here is the design and characterisation of such a system, which consists of a microfluidic chip, specifically developed for manipulating microbubbles using both optical and acoustic trapping. A laser vibrometer is used to observe the coupling of acoustic energy into the chip from a piezoelectric transducer bonded to the surface. Measurement of the velocity of surface waves on the chip is investigated as a potential method for inferring the nature of the acoustic fields excited within the liquid medium of the device. Comparison of measured surface wavelengths with wave types suggests the observation of anti-symmetric Lamb or Love-Kirchhoff waves. Further visual confirmation of the acoustic fields through bubble aggregation highlights differences between the model and experimental results in predicting the position of acoustic pressure nodes in relation to excitation frequency.

Friday, 14 March 2014

Harrie Massey Lecture 2014 by Prof Steven Chu

Professor Steven Chu (1997 Nobel Laureate in Physics and former US Secretary of Energy) will give the 2014 Harrie Massey Lecture at UCL on Energy and Climate Change: Challenges and Opportunities, Wed 19 Mar 14.

Abstract: Science and technology has profoundly transformed the lives of much of humanity. The industrial and agricultural revolutions are also changing the future destiny of our planet. I will discuss the necessity, challenges, and opportunities in innovation and policy that will be needed to transition to a sustainable future.

Monday, 10 March 2014

NanoSpain 2014

Phil is giving a talk at the NanoSpain 2014 conference in Madrid, 11-14 Mar 14 on Evanescent wave optical trapping and manipulation of particles and nanostructures.

Abstract:  Optical trapping is a powerful technique for the controlled manipulation of particles with sizes in the micron, sub-micron and nanometre range1.  Conventional optical tweezers using a single, strongly-focused laser beam to confine particles within the focal volume of ~1um3.  Optical binding describes the self-organisation of microparticles and nanostructures in an optical field that occurs over long distances and extended areas arising from the multiple scattering of light. Here we present experimental schemes for the control of optically bounds structures in evanescent optical fields.  The first relies on total internal reflection at an interface, where the evanescent field penetrates a short distance (comparable to, or less than the optical wavelength) above the interface.  We show that this geometry, shown in Figure 1(a), gives rise to one- and two-dimensional optically ordered structures of microparticles and also of nanostructures immersed in the field, shown in Figure 1(b) – (d), and quantify the binding forces and structure geometries via video microscopy2,3.
Figure 1: Optical binding of carbon nanostructures. (a) Set-up of the optical binding experiment; (b) Optically bound chain of carbono nanotube bundles; (c) When the laser beam is turned off the chain disintegrates; (d) Laser beam on, chain re-forms

The second geometry uses optical waveguides of sub-optical wavelength dimension.  For our experiments these are optical fibres that are adiabatically tapered to 1micron in diameter. Such a waveguide supports the fundamental mode only, but a large fraction of the power propagates in an evanescent field that can penetrate a significant distance in the surroundings.  We show here how this field can be used for optical binding of particles to the nanofibre and long-range transport along the length of the tapered region4.


References
1. O. M. Maragò, P. H. Jones, P. G. Gucciardi, G. Volpe & A. C. Ferrari. 'Optical trapping and manipulation of nanostructures', Nature Nanotechnology 8 807-819 (2013)

2. M. Sergides, S. E. Skelton, E. Karczewska, K. Thorneycroft, O. M. Maragó & P. H. Jones.  'Optically bound particle structures in evanescent wave traps', Proc. SPIE 8458, Optical Trapping and Optical Micromanipulation IX, 84583C, doi: 10.1117/12.929612 (2012)

3. S. H. Simpson, P. H. Jones, O. M. Maragò, S. Hanna & M. J. Miles. 'Opticalbinding of nanowires in counter-propagating beams’, Proc SPIE 8810 Optical Trapping and Optical Micromanipulation X, 881026, doi: 10.1117/12.2024466 (2013)

4. S. E. Skelton, M. Sergides, R. Patel, E. Karczewska, O. M. Maragó & P. H. Jones. 'Evanescent wave optical trapping and transport of micro- and nanoparticleson tapered optical fibers', Journal of Quantitative Spectroscopy and Radiative Transfer 113 2512-2520 (2012)

Monday, 24 February 2014

Symposium on Optical Forces: from atoms to soft-matter

On Wed 26 Feb 14 the OSA Messina Student Chapter and EPS Young Minds Group Messina wil be holding a one-day symposium on Optical Forces at the IPCF-CNR (Messina). The programme for the day includes:

  • J. J. Saenz (University of Madrid) Scattering asymmetry and non-conservative optical forces on small particles (OSA Lecture)
  • P. H. Jones (University College London) Evanescent wave traps and optical binding of particles
  • G. Pesce (University of Naples) Surface charge and hydrodynamic coefficient measurements of micro-particles and living micro-organisms by Optical Tweezers
  • M. G. Donato (IPCF-CNR) Optical trapping of nanostructures
  • C. J. Foot (University of Oxford) Laser cooling and trapping of atoms – past and present (Young Minds Lecture)
  • G. Volpe (Bilkent University) Speckle optical tweezers: Tunable anomalous diffusion and selective optical manipulation
  • O. M. Maragò (IPCF–CNR) Fano-Doppler laser cooling of hybrid nanostructures

Monday, 10 February 2014

Xiang Han joins the Optical Tweezers Group

Xiang Han has joined the UCL Optical Tweezers Group as a visiting student.   Xiang is a PhD student in the College of Optoelectronic Science & Engineering at the National Defense University, Changsha, Hunan, China.  His visit is funded by an award from the China Scholarship Council.  Xiang will be working with us until 2016 on a number of optical binding experiments.

Monday, 16 December 2013

PhD studentship available

A PhD studentship is available to start in September 2014 on a project entitled Membrane engineering of artificial lipid vesicles. The goal of this project is to use optical tweezers to probe the mehanical properties of biomimetic vesicles undergoing temperature or light-induced phase or structural transformation, and to use the results of these studies to engineer membrane materials with properties optimised for applications including controlled drug release and microreactors.

Experimental work will be carried out in the Optical Tweezers Group in the Department of Physics & Astronomy at UCL and in the Biological Soft Matter Group in the School of Materials Science at the Japan Advanced Institute of Science & Technology (JAIST).  The project is jointly supervised by Dr Phil Jones (UCL) and Dr Tsutomu Hamada (JAIST).

The studentship will pay a stipend and fees at the rate applicable for UK/EU students for three years.  The student will be registered for a PhD at UCL where they will spend the first and third years.  The second year of the PhD will be spent at JAIST.

Please contact Dr Phil Jones for further details or to express an interest.

Monday, 2 December 2013

AMOP Physics Open Day

The Atomic Molecular Optical and Positron Physics group will be holding an Open Day on Wednesday December 4th 2013 at 13:00.  The Open Day will be held in rooms A1 and E7 located on the Physics building on UCL's main Gower Street Campus. 

The agenda of the day is: 
13:00 - 15:00  Short research presentations by AMOPP faculty (A1)
15:00 - 18:00  Poster presentations by research groups (E7)
15:00 - 17:00 Lab tours

Please see here for further details of how to get to us.