Nicolò Accanto | Searcharxiv

arXiv2013

Second harmonic nano-particles for femtosecond coherent control on the nanoscale

We provide a complete toolkit for coherent control experiments on the nano-scale. By exploiting the second harmonic emission from single (150 nm) nonlinear nano-particles, we show that ultrafast femtosecond laser pulses can be compressed and controlled in time with unprecedented spatial accuracy. The method is tested on various nano-particles of different sizes, shapes and materials, both dielectric BaTiO3, Fe(IO3)3) and metallic (Au) thus demonstrating its robustness and versatility.

physics.optics↗

arXiv2011

Spin--flip Limited Exciton Dephasing in CdSe/ZnS Colloidal Quantum Dots

The dephasing time of the lowest bright exciton in CdSe/ZnS wurtzite quantum dots is measured from 5 K to 170 K and compared with density dynamics within the exciton fine structure using a sensitive three-beam four-wave-mixing technique unaffected by spectral diffusion. Pure dephasing via acoustic phonons dominates the initial dynamics, followed by an exponential zero-phonon line dephasing of 109 ps at 5 K, much faster than the ~10 ns exciton radiative lifetime. The zero-phonon line dephasing is explained by phonon-assisted spin-flip from the lowest bright state to dark exciton states. This is confirmed by the temperature dependence of the exciton lifetime and by direct measurements of the bright-dark exciton relaxation. Our results give an unambiguous evidence of the physical origin of the exciton dephasing in these nanocrystals.

cond-mat.mes-hall↗