Friday 25 February 2011

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)
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)

Thursday 17 February 2011

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

Wednesday 2 February 2011

Jaesuk Hwang seminar

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

AbstractA 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).