Nuffield Bursary Award

Ewa Karczewska has been awarded a Nuffield Foundation Undergraduate Research Bursary to work in the UCL Optical Tweezers Group this summer. This scheme allows UK undergraduates to gain research experience by providing funding for up to eight weeks to complete a research project during the summer vacation. We have hosted three previous Nuffield Foundation Bursary students: Muddassar Rashid (2008) who worked on synthesis and properties of polarisation vortex beams, Alex Dunning (2009) who performed calculations on the properties of optical nanofibres and is now studying for a PhD at Southampton University, and Radhika Patel (2010) who worked on photonic force microscopy experiments and is taking her final exams this year.

Optical Trapping Applications

Next week Phil, Susan and Marios will all be attending the OSA Optical Trapping Applications conference in Monterey, CA.  Phil will be giving a talk about our work on trapping with novel beams, and Susan and Marios will be presenting posters on their research projects.

Visit by Onofrio Marago

Onofrio Marago (NanoSoft Lab, IPCF-CNR, Messina) is visiting the group this week, 7-11 March 2011.

Onofrio has a long-running collaboration with the UCL Optical Tweezers Group and exchange visits between UCL and NanoSoft Lab are presently funded by our Royal Society International Joint Project.

Left: Onofrio adjusting the evanescent-wave optical binding experiment.

NPL Annual Review

The NPL-UCL Microbubble Project is featured in the latest NPL Annual Review, 110 Years of Impact.

Measuring with microbubbles

NPL is working with University College London on a fascinating project which investigates the dynamics of microbubbles, to see if they can be used as highly sensitive sensors in medical an industrial applications.

Microbubbles are specially-coated bubbles which are designed primarily to enhance ultrasound pulse-echo imagaing.  Their use significantly enhances sound echoes, thereby improving detection accuracy, and therefore diagnosis of 'difficult' cancers (e.g. liver, prostate).

Microbubbles (and specially designed ultrasonic fields) are being studied worldwide as possible vehicles for drug and gene delivery.  They promise to play a crucial role in fighting Alzheimer's disease, or cancers in which the use of chemotherapy is deemed too risky to the patient, and thus a targeted therapy is more effective.

NPL's work in this area is developing the measurement building blocks, to exploit the sensitivity of microbubbles to local changes in their environment, so extending their effectiveness in medical applications and beyond.

For more information about this project contact Phil Jones at UCL, or Gianluca Memoli at NPL.

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).