A. Le Calvez

Experimental study of the origin of the second-order nonlinearities induced in thermally poled fused silica

Second-harmonic generation (SHG) experiments at the surfaces and in the volumes of thermally poled commercial fused-silica samples have been performed. The experimental results show, for the first time to our knowledge and in agreement with our model, that second-order nonlinearity is induced on both cathodic and anodic interfaces. No contribution from the bulk of the sample could be detected. Moreover, our data also reveal that reorientable moieties are at the origin of the induced nonlinearity. The second-order susceptibility, evaluated by a surface SHG experiment, is chi((2))(333)~1 pm/V . The estimated susceptibility associated with the dc Kerr effect is negligible.

Ultrashort orientational dynamics of liquid crystals in the smectic-A phase

Abstract A femtosecond time-resolved optical Kerr effect experiment was carried out to study the reorientational motion of a series of cyanobiphenyl molecules around their long axis in the smectic-A phase. The Kerr effect was found to mainly result from the reorientation of the cyanobiphenyl core of the liquid crystal molecule. Three relaxation times were observed in the subpicosecond and picosecond range. They appear to be associated with libration and diffusive reorientations of chromorphores of individual and paired molecules. The analysis on several temporal scales reveals the existence of strong molecular interactions within the smectic-A layers.

Light-controlled erasure of induced χ(2) in thermally poled glasses

We demonstrate that the induced second order nonlinearity χ(2) generated in thermal poled doped borosilicate glasses can be erased by a prolonged exposure to near IR laser radiation. The evolution of the second harmonic signal with respect to laser time exposure, intensity and wavelength is reported. The IR laser radiation induced relaxation of the χ(2) is mainly related to two-photon absorption of the glass. The nonexponential time dependence of the second harmonic signal agrees with a simple model involving diffusion of photoexcited carriers. The reversible erasure process is also observed when the sample is exposed to near ultraviolet laser radiation.

Time-domain separation of nuclear and electronic contributions to the third-order nonlinearity in glasses

The electronic and nuclear contributions to the third-order nonlinearity of glasses are separated by use of 100-fs pulses in a time-resolved heterodyne optical Kerr effect technique. A direct estimate of the relative strengths of electronic and nuclear contributions was made by the comparison between the nuclear contribution deduced from the Raman spectra with the Kerr signal. The ratio between the electronic and nuclear response functions was ∼5/1 in a tellurium oxide glass sample. The time evolution of the nuclear contribution is in good agreement with results deduced from the Raman spectra.

Second harmonic field generated in reflection by an inhomogeneous nonlinear polarization

Abstract The second harmonic field reflected at an interface by a spatially inhomogeneous nonlinear polarization is calculated. We show that, through the spatial derivative of the nonlinear polarization, this spatial profile adds a new term to the reflected field calculated by Bloembergen and Pershan for a homogeneous nonlinear medium. The amplitude and phase of the additional term strongly alter both the amplitude and phase of the reflected field. The importance of this effect is illustrated in some meaningful physical cases.

Contrôle spatial de la non linéarité d'ordre deux induite par "poling" thermique dans les verres par effacement optique

We demonstrate that either one or two-photon absorption allow to tailor the spatial profile of second order susceptibility induced in a thermally poled borophosphate glasses. A law describing the phenomena is proposed.

Laser controlled erasure of the /spl chi//sup (2)/ induced in thermally poled glasses

Summary form only given. The occurrence of an induced /spl chi//sub ind//sup (2)/ /spl sim/1 pm/V has attracted lot of interest because it offers the prospect of monolithically integrated nonlinear optical systems. However, for frequency converters, one has to create a quasi-phase matching (QPM) condition. Recent experiments suggested this could be performed using collimated light beams. Hereafter, we report on the study of the erasure of the induced /spl chi//sub ind//sup (2)/ with respect to time exposure, laser intensity and wavelength in Nb/sub 2/O/sub 5/-borophosphate doped glasses.

Time domain separation of nuclear and electronic contributions to the third-order nonlinearity in glasses

We report the observation of a nuclear nonresonant vibrational contribution in glasses with 100-fs pulses. In the glasses studied, the nuclear contribution to the third-order nonlinearity varies from 15 to 20%. The over-dampened nuclear time responses are in very good agreement with Raman spectra. These results were achieved by means of heterodyne time-resolved optical Kerr measurements using 100-fs cw mode-locked Ti:sapphire pulses.

Femtosecond Analysis of the Spinning Motion of Liquid Crystal Molecules in Smectic A Phases

Analysis of the spinning motion of liquid crystal molecules is reported for the first time. A femtosecond pump probe Kerr effect experiment allowed us to evidence both individual and collective contributions to this motion.