Accueil > Équipes scientifiques > Dynamiques et Interactions : Rayonnement, Atomes, Molécules (DIRAM) > Offres de stage, thèses, post-docs > Photo-induced dynamics in nanoparticles
L3/M1 Internship (Physics)
Photo-induced dynamics in nanoparticles
L3/M1 Internship (Physics)
par - 6 septembre 2023
The photochemistry of nanoparticles (NP) has major implications for biology, nanotechnologies and energy conversion. Indeed, new photophysical processes which are not observed in isolated systems or in the condensed phase appear at the nanoscale, such as the formation of confined excitonic states [1] or non-linear effects related to the local amplification of the electromagnetic field.
We are interested in all the processes involved in the interaction between light and NPs [2] : from the strong non-linear effects that are observed at high laser intensities to the collective excitation that is first triggered to the following electronic relaxation that leads to the localized exciton formation and possible new reactivity. The laser-nanoparticle interaction can be finely controlled through spatial shaping of the laser beam and size-selection of particular nanoparticles (SiO2, NaCl, organic tryptophan NPs…). In a first step, we will characterize the laser-nanoparticle interaction by using a hypergaussian or exotic laser spatial profile, interacting with size-selected nanoparticles. When the optimal laser conditions are identified, we will investigate the relaxation dynamics of the particles, after a soft excitation of its excitonic states.
The experiments will be performed on the new femtosecond laser at ISMO providing 800 nm, 30 fs, 4.5 mJ pulses at 3 kHz repetition rate. A supersonic jet of NP interacts with the laser inside a Velocity Map Imaging Spectrometer (VMIS). The energy and angular distribution of the emitted photoelectrons and photo-ions carries the informations about the light-matter interaction at the femtosecond and nanometer scales. Experimental data will be analyzed with python scripts and artificial intelligence.
Contact : Lionel Poisson
[1] A. Lietard, et al., Self-trapping relaxation decay investigated by time-resolved photoelectron spectroscopyPhys. Chem. Chem. Phys. 20, 11206-11214 (2018).
[2] G. Gallician, "Effets d’anisotropie dans la photo-ionisation induite par laser ultracourt de molécules et de nanomatériaux isolés en phase gazeuse", Thèse de l’Université Paris-Saclay (2020).