Search results for " ultrafast"

Photocycle of Excitons in Nitrogen-Rich Carbon Nanodots: Implications for Photocatalysis and Photovoltaics

2020

Nitrogen-rich carbon nanodots have emerged as promising nanomaterials for a wide range of applications where a highly emissive and photoactive material with low toxicity and cost-effectiveness is required. One of their hallmarks is indeed a bright, tunable fluorescence of excitonic nature. Disentangling the origin of their optical absorption and fluorescence properties and uncovering relaxation channels and interactions with solvents are some of the most debated issues in the field. Uncovering these aspects is essential for targeted applications, especially in the fields of photocatalysis but also photovoltaics and optoelectronics. Here, we present dedicated transient absorption measurement…

Ultrafast broadband fluorescnce up-conversion of N-acetyl-L-tryptophanamide (NATA)

2011

Wideband THz time domain spectroscopy set-up based on ultrafast pulsed laser: model and experiments

2014

We present an analytical model describing the full electromagnetic propagation in a THz Time Domain Spectroscopy (THz-TDS) laser based system. We pay particular attention to the modelling of the time-frequency behavior of all the stages, which compose our experimental set-up. In particular, our model takes into account the following features: pump beam focusing into the generation crystal; phase-matching between pump and THz pulses inside both the generation and detection crystals; chromatic dispersion and absorption inside the materials; Fabry-Perot effect in both the crystals; diffraction along the propagation, focalization and overlapping between THz and probe beams; Electro-Optic Sampli…

High-order Kerr nonlinearity of air calibrated with transient molecular alignment

2009

Talk given by O. Faucher; International audience; Nonlinear electronic Kerr index of the major air constituents has been measured up to high order terms using transient molecular alignment as a reference. Sign reversal associated to negative nonlinearity is observed above a pulse intensity of 26 TW/cm^2.

Femtosecond Raman time-resolved molecular spectroscopy

2004

International audience; The applicability of several femtosecond time resolved non-linear coherent techniques such as Raman induced polarization spectroscopy (RIPS), degenerate four-wave mixing (DFWM) and coherent anti-Stokes Raman spectroscopy (CARS) for molecular spectroscopy is presented. All methods rely on the initial coherent excitation of molecular states producing wavepackets, whose time evolution is then measured. In the case of RIPS and DFWM only pure rotational transitions are involved, whereas in CARS vibrational states can be excited. First the methodology of concentration and temperature measurements using RIPS in gas mixtures involving N2, CO2, O2, and N2O is shown. In additi…

Emergent ultrafast phenomena in correlated oxides and heterostructures

2017

The possibility of investigating the dynamics of solids on timescales faster than the thermalization of the internal degrees of freedom has disclosed novel non-equilibrium phenomena that have no counterpart at equilibrium. Transition metal oxides (TMOs) provide an interesting playground in which the correlations among the charges in the metal $d$-orbitals give rise to a wealth of intriguing electronic and thermodynamic properties involving the spin, charge, lattice and orbital orders. Furthermore, the physical properties of TMOs can be engineered at the atomic level, thus providing the platform to investigate the transport phenomena on timescales of the order of the intrinsic decoherence ti…

Real-time observation of the charge transfer to solvent dynamics

2013

Intermolecular electron-transfer reactions have a crucial role in biology, solution chemistry and electrochemistry. The first step of such reactions is the expulsion of the electron to the solvent, whose mechanism is determined by the structure and dynamical response of the latter. Here we visualize the electron transfer to water using ultrafast fluorescence spectroscopy with polychromatic detection from the ultraviolet to the visible region, upon photo-excitation of the so-called charge transfer to solvent states of aqueous iodide. The initial emission is short lived (similar to 60 fs) and it relaxes to a broad distribution of lower-energy charge transfer to solvent states upon rearrangeme…

Negative and positive Kerr nonlinearity of air calibrated with transient molecular alignment

2009

Talk given by O. Faucher; International audience; Nonlinear electronic Kerr index of the major air constituents has been measured up to high order terms using transient molecular alignment as a reference. Sign reversal associated to negative nonlinearity is observed above a pulse intensity of 26 TW/cm^.2