Prof. Mikael KALL
from the Department of Physics, Chalmers University of Technology,Göteborg, Sweden:

Optically driven plasmonic nanorotors

Colloidal metal nanoparticles have drawn increasing attention in the field of optical trapping because their unique interactions with electromagnetic radiation, caused by surface plasmon resonance effects, enable a large number of nano-optical applications of high current interest, such as plasmon based biochemical sensing, surface-enhanced Raman spectroscopy and optothermal control at the nanoscale. We found that single-crystal gold nanorods with sidelengths of the order 160 nm could be easily trapped and manipulated by laser tweezers inside thin liquid cells compatible with standard optical microscopy. The nanorods could be rotated extremely, reaching rotation frequencies above 40 kHz (2.5e6 r.p.m.), by applying circularly polarized laser light with power as low as a few mW. To the best of our knowledge, this is the fastest rotation of any kind of object, natural or man-made, in a liquid environment. The driving torque, caused by transfer of photon angular momentum (spin), is dominated by plasmonic resonant scattering rather than absorption, which drastically reduces laser-heating effects.

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Prof. Romain QUIDANT
from ICFO – The Institute of Photonic Sciences, Barcelona, Spain:

Nano-optomechanics with an optically levitated nanoparticle

We present our latest advances in nano-optical trapping and nano-optomechanics. We first introduce the use of an optically levitated nanoparticle in vacuum as a nano-optomechanical system with unprecedented performances. We describe its unique linear and nonlinear mechanical properties including its ultra-high force sensing capability and bi-stable dynamics. Subsequently, we present our efforts in cooling the oscillator motion towards mechanical ground state at room temperature. In particular, we present an experiment that combines active parametric feedback cooling with passive resolved side band cooling. The last part of the talk focuses on trapping nanoscale objects in the optical near field of resonant plasmonic nanostructures. Similar to the optical spring effect in high-finesse optical cavities, we demonstrate a pronounced back action effect that both increases the object confinement and relaxes the requirements on the minimum intra-cavity field intensity.

Contact : genet@unistra.fr