P. Masselin

Enhancement of second-harmonic generation with femtosecond laser pulses near the photonic band edge for different polarizations of incident light

We present experimental evidence of enhancement of second-harmonic generation as a result of an increase of the fundamental-field energy density within a multilayer structure near the photonic band edge.

Direct laser writing of buried waveguide in As2S3 glass using a helical sample translation

We report the fabrication and the characterization of buried waveguide in As(2)S(3) glass. It is well known that the interaction of femtosecond pulses with this material at high laser repetition rates results in a mainly negative refractive index variation, due to heat accumulation effect. However, we show here that a helical translation of the sample parallel to the laser beam, allows the inscription of a core of positive refractive variation, with full control over its magnitude and diameter. An example demonstrating the high symmetry of the guided mode is given.

Four-wave mixing in one-dimensional photonic crystals: inhomogeneous-wave excitation

We present what is to our knowledge the first study of nonlinear four-wave mixing in one-dimensional photonic crystals. The possibility of inhomogeneous-wave excitation at the four-wave mixing frequency ω3=2ω1-ω2 for two noncollinear beams of femtosecond laser pulses is demonstrated. As a result of this effect the wave at the frequency of four-wave mixing may be guided along the surface of the photonic crystal. Experiments of this type open the possibility of development of a new tool based on photonic crystal devices for coherent Raman spectroscopy of surfaces and of nanometer and submicrometer scale layers.

Spatially resolved Raman analysis of laser induced refractive index variation in chalcogenide glass

We report a detailed 2D μ-Raman analysis of the refractive index modification (Δn) induced by femtosecond laser filament in the bulk of Ge-Ga-S ternary chalcogenide glass. The invariant illumination and detection geometry during the 2D scanning, allows both qualitative and quantitative determination of the proportion of different structural units to be carried out. The results indicate that during the light-matter interaction, S3Ga-GaS3 ethane like groups are transformed into triclusters of Ga/S. The decreased population of edge- and corner-sharing GeS4/2 tetrahedra implies the formation of mixed triclusters : T/S where T = Ga and/or Ge. Finally, correlations between photostructural changes and Δn are presented.

Experimental observation of the interference of three- and five-wave mixing processes into the signal of second harmonic generation in bacteriorhodopsin solution

Abstract The second harmonic (SH) generation with a Ti:sapphire femtosecond laser system in a randomly oriented suspension of finely fragmented purple membranes of Halobacterium halobium has been studied experimentally. The existence of two interfering contributions to the SH signal due to second- and fourth-order nonlinear processes has been established. The phase and the value of the fourth-order electronic susceptibility (hyperpolarizability) relative to the second-order ones have been determined. The analysis of the experimental data shows the existence of a coherent contribution into the SH signal.

Free carrier accumulation during direct laser writing in chalcogenide glass by light filamentation

We present direct laser writing of channels in chalcogenide glass under light filamentation conditions. Because of the intrinsic properties of the filament, the positive refractive index profile of the channels exhibits a cylindrical symmetry of high quality. The role of the repetition rate is also investigated. It is shown that if the time separation between pulses is shorter than the lifetime of the plasma, the free carriers accumulate and induce a larger variation of the refractive index.

Nonlinear process in photonic crystals under the noncollinear interaction

We analyzed theoretically and studied experimentally the sum-frequency generation and four-wave-mixing processes under the noncollinear geometry of interaction in finite-length periodic photonic crystals. The efficiency of the surface and the bulk mechanisms of sum-frequency generation are compared. It is shown that surface and bulk mechanisms cannot be separated on the polarization of the sum-frequency signal only but that the angular dependencies of the sum-frequency signal intensity enable us to separate them. The excitation of inhomogeneous waves at the four-wave-mixing frequency of ω3=2ω1-ω2 is discussed and demonstrated.

Laser filamentation in chalcogenide glass

We report laser filamentation in the bulk of chalcogenide glass with femtosecond laser pulses of energy on the nanojoule level. Spatially resolved measurements of the resulting refractive index modification are presented. The study of the pulse energy and focusing condition dependencies show that channels of positive refractive index variation of several millimeter length can easily be obtained.

Direct laser writing of a low-loss waveguide with independent control over the transverse dimension and the refractive index contrast between the core and the cladding

In this Letter, we present the realization of a low-loss waveguide in a chalcogenide glass by direct laser writing technique in a particular configuration that allows the independent control over the diameter of the core and the magnitude of the refractive index contrast with the cladding. The waveguide is of multicore type and composed of 19 channels arranged on a hexagonal lattice. Each channel is obtained by stacking voxels of refractive index variation obtained by static exposure to femtosecond laser pulse burst. The distance between the channels can be used to vary the diameter of the waveguide, while the duration of laser burst controls the magnitude of the effective index and the propagation loss. We demonstrate that it can be reduced down to 0.11 dB/cm.

Experimental observation of the interference of three-and five-wave mixing processes in optical second harmonic generation in a solution of bacteriorhodopsin

The generation of a femptosecond second harmonic in a bacterior-hodopsin solution is investigated. It is shown that the behavior of the harmonic can be explained by the coherent interference of several contributions from three-and five-wave mixing processes (χ(2) and χ(4)). The magnitude and phase of the fourth-order electronic susceptibility χ(4) of the medium with respect to χ(2) are determined.