UCL Physics Society Talk

Phil is giving a talk the the UCL undergraduate Physics Society, Tue 02 Jun 15 titled "Pull, push, spin, squeeze: optical forces on microparticles."

Abstract:  In this talk I will explain how the interaction of laser light with matter can give rise to a force or torque that, if the particle is small enough, can have a significant effect on its motion.  I will then go on to describe a number of experiments from the UCL Optical Tweezers Group that use optical forces in a variety of experimental geometries (optical tweezers, optical fibre traps, optical binding) and applied to a range of different objects, including nanostructures and biological material.

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

Fluctuations in Dynamical Systems Far From Equilibrium

The workshop will bring together people from applied mathematics, dynamical systems, condensed matter physics and statistical physics. The theme are fluctuations far from equilibrium, particularly in stochastic dynamics. A focus will be on so-called fluctuation relations, which generalize the second law of thermodynamics to small systems. They have been found to be generally valid very far from equilibrium. This active, recent topic of research will be discussed both from a theoretical and from an experimental point of view. Cross-links to large deviation theory and to anomalous stochastic processes will be explored.

Programme

11.30 - 12.30 Ian Ford, UCL: A rough guide to fluctuation relations

14.00 - 15.00 David Carberry, University of Bristol: Fluctuation Relations: Experimental Demonstrations

15.00 - 16.00 Adrian Baule, QMUL: Exact relations in non-equilibrium statistical mechanics

16.30 - 17.30  Nicholas Watkins, Cambridge, UK: Anomalous Diffusion, Anomalous Time Series, and the models that describe them

All talks will be held in seminar room M103 (first floor) of the Department of Mathematics at Queen Mary University of London.

For more information contact Prof Ferruccio Renzoni

David Carberry visit and seminar

David Carberry (Bristol University) is visiting and giving the AMOP Physics seminar on Wednesday 22 February.  David works on optical micromanipulation techniques and recently demonstrated a multi-point holographic optical tweezers controlled through an iPad.  The abstract for his seminar is below:

Title:  Non-spherical optically trapped probes: Design, control and applications
Abstract: Non-spherical probe particles have a number of advantages over microspheres: rotational motion may be monitored and controlled, the trapping points may be removed from the probe’s tip, and the tip can be more accurately positioned than a microsphere of equivalent radius.

We demonstrate a range of non-spherical probes, and discuss how they may be tailored to specific applications. We consider how probe geometry affects the region of space the tip explores – the ‘tip thermal volume’, and the relaxation times of this motion¹. By independently position-clamping translational and rotational modes in different ways, we are able to further control the shape of the tip thermal volume, and dramatically improve the position resolution of the probe, with no reduction in force sensitivity².

Using holographic optical tweezers combined with stereomicroscopy, we can both control and track the motion of our non-spherical probes in all three dimensions. Finally, we demonstrate the use of our probes to image surfaces in 3D³, and measure force and torque interactions with biological specimens. 

  

1. S.H. Simpson and S. Hanna. ‘Thermal Motion of a holographically trapped SPM-like probe’. Nanotechnology, 20 395710 (2009)
2. D.B. Phillips et al. ‘Position clamping of optically trapped microscopic non-spherical probes’. Optics Express, 19 20622 (2011)
3. D.B. Phillips et al. ‘Surface imaging using holographic optical tweezers’. Nanotechnology, 22 285503 (2011)

Harrie Massey Lecture

Prof Niek van Hulst (ICFO Barcelona) is visiting the UCL Physics Department today and giving the annual Harrie Massey Lecture on the topic of Coherent control of single molecules, complexes and nanoantennae.

Abstract: The observation of quantum mechanical effects in biological systems, such as light-harvesting antennae, has opened a lively debate as to the role of coherences in natural systems. Traditionally, such coherences are probed by manipulating quantum interference effects with shaped laser pulses. Yet the intrinsic structural inhomogeneity and environmental fluctuations of complex systems at ambient conditions average out most oscillatory spectroscopic features. Only by “single molecule detection” one can hope to catch a glimpse through the disorder. This lecture will present coherent control of single molecules, allowing both observation and manipulation of vibrational wave-packet interference and Rabi-oscillations in individual molecules at ambient conditions. The single-molecule approach ensures that the ultimate degree of coherent control can be realized. We have applied our novel method to single light-harvesting complexes and optical nanoantennas. Recent results on ultrafast quantum coherent energy transfer and femtosecond control of nanoscale hotspots will be presented.

Physics Department Colloquium

Dr Gavin Crooks (Lawrence Berkeley National Laboratory, University of California Berkeley) will be giving this term's Departmental Colloquium today, Wed 19 Oct, on Statistical Thermodynamics and the Breaking of Time Symmetry.

Abstract: The irreversible dissipation of energy is directly related to the breaking of time reversal symmetry. I will discuss some of the implication of these phenomena to microscopic, driven non-equilibrium systems, such as single molecular force-extension experiments, biological molecular motors and artificial photosynthesis.

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.

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.

UCL sp2 Carbon Group

Phil is giving a talk to the UCL sp2 Carbon Group on 'Optical Trapping of Carbon Nanomaterials'

This talk will give a brief overview of our experimants on optical tweezers for trapping and maniplation of carbon nanomaterials, including nanotubes and graphene flakes.  It will start with a description of
the experimental techniques of opical trapping and back focal plane interferometry for paricle tracking, then present results on trapping, tracking and the analysis of Brownian motion of trapped carbon nanotube bundles and graphene flakes, including centre-of-mass and angluar fluctuations and driven rotations, and combined optical tweezers and Raman spectroscopy.


References:
O. M. Maragò, F. Bonaccorso, R. Saija, G. Privitera, P. G. Gucciardi, M. A. Iatì, G. Calogero, P. H. Jones, F. Borghese, P. Denti, V. Nicolosi & A. C. Ferrari. 'Brownian motion of graphene', ACS Nano 4 7515-7523 (2010)

O. M. Maragò, R. Saija, F. Borghese, P. Denti, P. H. Jones, E. Messina, G. Compagnini, V. Amendola, M. Meneghetti, M. A. Iatì, and P. G. Gucciardi.  'Plasmon-enhanced optical trapping of metal nanoparticles: force calculations and light-driven rotations of nanoaggregates', Proc. SPIE Vol. 7762, 77622Z (2010)

O. M. Maragò, P. G. Gucciardi and P. H. Jones.  'Photonic Force Microscopy: from femtonewton force sensing to ultra-sensitive spectroscopy', in Scanning Probe Microscopy in Nanoscience and Nanotechnology 1 (Springer) B. Bushan (Ed.) (2010)

P. H. Jones, F. Palmisano, F. Bonaccorso, P. G. Gucciardi, G. Calogero, A. C. Ferrari & O. M. Maragò.  'Rotation detection in light-driven nanorotors',  ACS Nano 3 3077-3084 (2009)

O. M. Maragò, P. H. Jones and A. C. Ferrari. 'A light touch on nanotubes: femtonewton force sensing and nanometric spatial resolution', SPIE newsroom, doi 10.1117/2.1200901.1475 (2009)

O. M. Maragò, P. H. Jones, F. Bonaccorso, V. Scardaci, P. G. Gucciardi, A. Rozhin, and A. C. Ferrari.  'Femtonewton Force Sensing with Optically Trapped Nanotubes', Nano Letters 8 3211-3216 (2008)

O. M. Maragò, P. G. Gucciardi, F. Bonaccorso, G. Calogero, V. Scardaci, A. Rozhin, A. C. Ferrari, P. H. Jones, R. Saija, F. Borghese, P. Denti & M. A. Iatì.  'Optical trapping of carbon nanotubes’, Physica E 40 2347-2351 (2008)

Optical Techniques in Biological Physics Meeting

The Biological Physics Group of the Department of Physics and Astronomy is hosting a half-day meeting on Thursday 17 February, on the subject of 'Optical Techniques in Biological Physics'.  The meeting brings together researchers from the physical and life sciences with an interest in optical techniques (imaging, spectroscopy, optical traps, etc) for a series of short talks and discussions on opportunities for future interdisciplinary work.  The programme for the day is:

2.00 Introduction (Phil Jones)
2.10 Clare Elwell (Medical Physics & Bioengineering) The use of near infra-red spectroscopy to measure tissue oxygenation, haemodynamics and metabolism
2.40 Angus Bain (Physics) Time-resolved fluorescence studes of biomolecular structure, interactions & dynamics
3.10 Angus Silver (NPP) The acousto-optics lens two-photon microscope and its application to neuroscience
3.40 Tea break
4.00 Chris Thrasivoulou (Cell & Developmental Biology) title tbc
4.30 Guillaume Charras (LCN) Imaging challenges in molecular cell biology
5.00 Open discussions

Jaesuk Hwang seminar

Jaesuk Hwang (Imperial College) is visiting and giving today's AMOPP seminar on 'Quantum nanophotonics with single molecules'.

Abstract:  A new type of atom-photon interface is proposed that can be used as a resource for processing quantum information. Individual organic dye molecules will be deposited close to optical waveguides on a photonic chip.

At cryogenic temperature, the molecules act as simple two-level atoms with a strong electric dipole transition.  They can be individually addressed and they remain trapped indefinitely in the solidified solvent. We demonstrated that a single molecule can obscure a substantial part of the light in a beam whose cross section is comparable to the scattering cross section of the molecule [i].  In such a beam, we showed that the molecule behaves as a two-level quantum emitter whose nonlinear response is appreciable even at very low light intensity.  This was seen through the appearance of Mollow sidebands in the fluorescence spectrum of the molecule.  The relative merits of absorption and fluorescence as a method of detecting single molecules were discussed in ref [ii]. In another proof of the large dipolar coupling we were able to observe Rabi flopping of the two-level molecule in weak light pulses, where only a few hundred photons were enough to generate a p-pulse [iii]. Most recently, we showed that the single molecule can act as an absorber whose absorption coefficient can be manipulated by a control laser and can also be turned into gain when the population of the molecule is inverted [iv].  All-optical nonlinear operation at the single emitter level has been deemed exceptionally challenging and only been considered in high-finesse microcavities. Here, we demonstrate that such operation is possible with single molecules with a propagating laser beams and discuss the possibility of building a quantum network on an optical waveguide chip.

 At cryogenic temperature, the molecules act as simple two-level atoms with a strong electric dipole transition.  They can be individually addressed and they remain trapped indefinitely in the solidified solvent. We demonstrated that a single molecule can obscure a substantial part of the light in a beam whose cross section is comparable to the scattering cross section of the molecule [i].  In such a beam, we showed that the molecule behaves as a two-level quantum emitter whose nonlinear response is appreciable even at very low light intensity.  This was seen through the appearance of Mollow sidebands in the fluorescence spectrum of the molecule.  The relative merits of absorption and fluorescence as a method of detecting single molecules were discussed in ref [ii]. In another proof of the large dipolar coupling we were able to observe Rabi flopping of the two-level molecule in weak light pulses, where only a few hundred photons were enough to generate a p-pulse [iii]. Most recently, we showed that the single molecule can act as an absorber whose absorption coefficient can be manipulated by a control laser and can also be turned into gain when the population of the molecule is inverted [iv].  All-optical nonlinear operation at the single emitter level has been deemed exceptionally challenging and only been considered in high-finesse microcavities. Here, we demonstrate that such operation is possible with single molecules with a propagating laser beams and discuss the possibility of building a quantum network on an optical waveguide chip.

[i] G. Wrigge, I. Gerhardt, J. Hwang, G. Zumofen, V. Sandoghdar, Nature Physics 4, 60 (2008).

[ii] G. Wrigge, J. Hwang, I. Gerhardt, G. Zumofen, V. Sandoghdar, Opt. Express 16, 17358 (2008).

[iii] I. Gerhardt, G. Wrigge, G. Zumofen, J. Hwang, A. Renn, V. Sandoghdar, Phys. Rev. A. 79 011402(R) (2009).

[iv] J. Hwang, M. Pototschnig, R. Lettow, G. Zumofen, A. Renn, S. Goetzinger, V. Sandoghdar, Nature 76 460 (2009).

Gerard Milburn Seminar

Prof Gerard Milburn (University of Queensland) is giving an AMOPP seminar on Quantum measurement and control of optomechanical systems.

Abstract: The emerging field of quantum optomechanics combines quantum optics and new fabrication techniques to control the quantum state of macroscopic mechanical resonators. This now provides a new approach for controlling the mutual interaction between light and mesoscopic structures, which is one of the eminent goals in quantum information science and of importance for fundamental experiments at the quantum-classical boundary. I will give an overview of this new field and discuss some specific models. These include a scheme to conditionally prepare a macroscopic mechanical resonator in an energy eigenstate by measurement, single photon optomechanics, and quantum entanglement in optomechanical networks

David McGloin Visit and Seminar

David McGloin (Dundee University) is visiting and giving the AMOPP/BioP seminar on Optical manipulation of droplets: aerosols and hydrosomes.

Abstract: In this talk I will discuss work in which my group has developed techniques to optical manipulate liquid droplets in both the air (aerosols) and in another liquid phase (hydrosomes). I will look at hope the optical manipulation of airborne droplets is subtly different from the trapping of particles in liquids in that one can access underdamped particle dynamics in contrast to the conventional heavily overdamped optical tweezers. I will touch on different technqiues for sizing such particles and how droplet composition can be determined using enhanced spectroscopic methods. In addition I will also touch on how optical fields can also be used to manipulate lqiuid droplets in an oil phase, both through direct optical forces and through thermal manipulation, and how this could lead to interesting ways to develop new forms of biological well plates.

Paola Borri Visit and Seminar

Paola Borri (Cardiff University) is visiting today and giving the AMOPP/BioP seminar on Novel Multiphoton Microscopy Techniques for Cell Imaging:  CARS Microscopy and Resonant Four-Wave Mixing.

Abstract:  Optical microscopy is an indispensable tool that is driving progress in cell biology, and is still the only practical means of obtaining spatial and temporal resolution within living cells and tissues. Much effort is being devoted recently to achieve intrinsic three-dimensional (3D) spatial resolution by exploiting optical nonlinear effects which can only take place in the small focal volume where high photon densities are reached. One of the most utilised multiphoton (ie nonlinear) microscopy techniques is two-photon fluorescence where the biomolecules of interest are labelled with fluorophores, which are optically excited via simultaneous absorption of two photons. However, these modified biomolecules raise questions if their behaviour is real or artefactual. Furthermore, all organic fluorophores are prone to photo-bleaching which severely limits time-course observations and is accompanied by toxicity effects and consequent cell damage.
Coherent Antistokes Raman Scattering (CARS) microscopy has recently emerged as a new multiphoton microscopy technique which overcomes the need of fluorescent labelling and yet retains biomolecular specificity and intrinsic 3D resolution. We have developed in our laboratory a fully home-built CARS microscope featuring innovative CARS excitation/detection schemes. In particular, we have demonstrated differential-CARS (D-CARS) and single-laser CARS utilising femtosecond laser pulses linearly chirped by glass dispersion. Furthermore we have invented and demonstrated a novel imaging modality, based on the resonant Four-Wave Mixing (FWM) of colloidal nanoparticles. Results on this work showed that nanoparticles, both semiconductor and metallic, can be used as alternative labels beyond fluorescence by exploiting their resonant FWM, to achieve a novel coherent multiphoton microscopy modality free from background and with a spatial resolution significantly surpassing the one-photon diffraction limit. I will present our latest progress with both techniques and their applications to cell imaging.

Nuffield Bursary Update (3)

Throughout the course of her Nuffield Foundation project this summer Radhika Patel will be making updates of her progress on our blog.  Her third instalment is below. 

Radhika writes: We wanted to improve the optical tweezers setup I have been working on so this week we partly dismantled the microscope was in order to get a better look at what was inside. Having made some adjustments, Susan and I have returned to aligning the beams, trapping particles and calibrating the trap again. In addition to this, we have started the process of integrating some optical fibres into the setup. Part of the last week was spent learning how to cut and prepare the fibres for use in the setup and actually connectorising some of the fibres.

Phil, Marios and I attended Richard Berry's lecture on Single-molecule observations of turnover, co-operativity and mechanochemistry in a macromolecular complex. As this was the first talk I had attended related to optical tweezing, it was interesting to hear about some of its applications.

Richard Berry Seminar

Richard Berry (Oxford) will be giving the CoMPLEX seminar on Tuesday 27 July on Single-molecule observations of turnover, co-operativity and mechanochemistry in a macromolecular complex.

Abstract: The bacterial flagellar motor has long been a canonical macromolecular complex because of the relative ease with which its output, rotation of the extracellular flagellar filament, can be observed.  In vivo imaging of GFP-labelled components of the motor has revealed that the motor is not a static structure, but that individual proteins are constantly replaced at rates on the order of 1/minute.  Localization at nanometre precision of labels attached to the motor, at frame rates of several to many kilohertz, has also allowed observations of the mechanism of co-operative directional switching in the motor and of its mechanochemical cycle.