Control of the Refractive Index in Photopolymerizable Materials for (2+1)D Solitary Wave Guide Formation

We report an experimental and theoretical study on the optimization of (2+1)D self-written waveguide formation inside a photopolymerizable material. The accurate control of the refractive index value inside the bulk of the material during the polymerization process gives us the opportunity to define a virtual core and a virtual cladding for the system. The V value which characterizes the guidance properties of a fiber can be applied to this propagation. The control of the V value allows us to propagate single mode or multimode waveguides on a few centimeters. Numerical simulations of these waveguides based on a paraxial model including both photopolymerization and Kerr effect give very good agreement with our experimental results

Sum-frequency generation in sol-gel material doped with binaphthol

A sum-frequency imaging system is used to investigate optical activity in a sol-gel material doped with the chiral molecule binaphthol. We show that this material can be optically structured to embed information that can be retrieved by sum-frequency

Versatile dual stage tunable NOPA with pulse duration down to 17 fs and energy up to 3 µJ at 500 kHz repetition rate

We report on a new ultrashort NOPA tunable between 500 and 1000 nm. It delivers pulse energies up to 3,1 microJand pulse duration down to 17 fs at 500 kHz

Excitonic spin relaxation in GaN

By performing non-degenerate pump-probe experiments, we study the relaxation dynamics of spin-polarized A and B excitons in wurtzite epitaxial GaN. We show that the spin relaxation of the exciton as a whole is negligible with regard to the spin relaxation of the individual carriers. We determined $T_{e} = 15$ ps for the electron in the conduction band, $T_{hh} = 5$ ps, and $T_{lh} = 1.5$ ps for the heavy hole (HH) and for the light hole (LH), respectively. The quite long HH relaxation time can be related to the band structure in which the degeneracy between different spin-valence bands is lifted

Caractérisation temporelle et spectrale de la photoluminescence de boîtes quantiques de CdZnTe

Nous étudions la relaxation des paires électron-trou dans des échantillons de boîtes quantiques auto-assemblées de CdZnTe riches en cadmium incluses dans un puits quantique riche en zinc. Dans ce type de système, le couplage électron-phonon LO est le principal mécanisme responsable de la relaxation d'énergie des porteurs. Nous mesurons cette relaxation par photoluminescence résolue en temps, en fonction de l'intensité et de l'énergie de photon de l'excitation

Coherent control and quantum kinetics of LO-phonon emission in CdZnTe quantum wells

We study the quantum kinetics of LO-phonon cascade emission in quantum wells by electron-hole pairs, whose relaxation ends with a trapping in quantum dots. Modulations with a period given by the LO-phonon frequency appear progressively in the time resolved differential transmission spectrum, indicating the transition from the quantum kinetic to the classical regime

Broadband ultrafast spectroscopy using a photonic crystal fiber: application to the photophysics of malachite green

International audienceFemtosecond single-pulsed supercontinua (SC) are produced in a short sub-cm piece of photonic crystal fiber. The SC span from 450 nm to more than 1.1 μm with 1-nJ energy injection. UV light down to 340 nm is observed with increased injection power. Using such a single-pulsed SC we implemented a compact transient absorption spectrometer with broadband detection and 150-fs FWHM time resolution to monitor the ultrafast dynamics of the electronic states of malachite green in ethanol excited to the S2 state. The full spectral evolution is observed from 450 nm to 1050 nm, with high sensitivity and a signal-to-noise ratio as high as 1000