Valentin Besse

Structure, nonlinear properties, and photosensitivity of (GeSe_2)_100-x(Sb_2Se_3)_x glasses

Chalcogenide glasses from (GeSe2)​100-​x(Sb2Se3)​x system were synthesized, with x varying from 5 to 70, in order to evaluate the influence of antimony selenide addn. on nonlinear optical properties and photosensitivity. Nonlinear refractive index and two photon absorption coeffs. were measured both at 1064 nm in picosecond regime using the Z-​scan technique and at 1.55 μm in femtosecond regime using an original method based on direct anal. of beam profile change while propagating in the chalcogenide glasses. The study of their photosensitivity at 1.55 μm revealed highly glass compn. dependent behavior and quasi-​photostable compns. have been identified in femtosecond regime. To better understand these characteristics, the evolution of the glass transition temp., d. and structure with the chem. compn. were detd.

Nonlinear characterization of materials using the D4σ method inside a Z-scan 4f-system

We show that direct measurement of the beam radius in Z-scan experiments using a CCD camera at the output of a 4f-imaging system allows higher sensitivity and better accuracy than Baryscan. One of the advantages is to be insensitive to pointing instability of pulsed lasers because no hard (physical) aperture is employed as in the usual Z-scan. In addition, the numerical calculations involved here and the measurement of the beam radius are simplified since we do not measure the transmittance through an aperture and it is not subject to mathematical artifacts related to a normalization process, especially when the diffracted light intensity is very low.

Building patterns by traveling dipoles and vortices in two-dimensional periodic dissipative media

Abstract We analyze pattern-formation scenarios in the two-dimensional (2D) complex Ginzburg–Landau (CGL) equation with the cubic–quintic (CQ) nonlinearity and a cellular potential. The equation models laser cavities with built-in gratings, which stabilize 2D patterns. The pattern-building process is initiated by kicking a compound mode, in the form of a dipole, quadrupole, or vortex which is composed of four local peaks. The hopping motion of the kicked mode through the cellular structure leads to the generation of various extended patterns pinned by the structure. In the ring-shaped system, the persisting freely moving dipole hits the stationary pattern from the opposite side, giving rise to several dynamical regimes, including periodic elastic collisions, i.e., persistent cycles of elastic collisions between the moving and quiescent dissipative solitons, and transient regimes featuring several collisions which end up by absorption of one soliton by the other. Still another noteworthy result is the transformation of a strongly kicked unstable vortex into a stably moving four-peaked cluster.

Spatially resolved phase objects using Mach–Zehnder interferometry

Phase characterization with a good spatial resolution is crucial for focused beams in nonlinear media. The phase-shifting interferometry technique, using the least-squares error criterion for several interferograms, is implemented using a reflective spatial light modulator (SLM). The method provides a convenient calibration for any phase-shift steps. The reliability of the proposed method is checked by direct comparison with results obtained by the Fourier transform method as well as using a previously characterized circular phase object.

Pattern Formation by Traveling Localized Modes in Two-Dimensional Dissipative Media with Lattice Potentials

We analyze pattern-formation scenarios in the two-dimensional (2D) complex Ginzburg-Landau (GL) equation with the cubic-quintic nonlinearity and a cellular potential. The equation models laser cavities with built-in gratings, which stabilize 2D patterns. The pattern-building process is initiated by kicking a compound mode, in the form of a dipole, quadrupole, or vortex which is composed of four local peaks. The hopping motion of the kicked mode through the cellular structure leads to the generation of various extended patterns pinned by the structure. In the ring-shaped system, the persisting freely moving dipole hits the stationary pattern from the opposite side, giving rise to several dynamical regimes, including periodic elastic collisions, i.e., persistent cycles of elastic collisions between the moving and quiescent dissipative solitons, and transient regimes featuring several collisions which end up by absorption of one soliton by the other. Another noteworthy result is transformation of a strongly kicked unstable vortex into a stably moving four-peaked cluster.

Third- and fifth-order optical nonlinearities characterization using the D4σ-Z-scan method

We solved analytically the equations governing the evolution of the intensity and phase shift inside a nonlinear medium taking into account third- and fifth-order nonlinear susceptibilities. We give explicit expression of the propagation distance and the phase shift versus the output intensity. This solution is inverted numerically by means of Newtons method. The result does not apply to some special cases due to the vanishing of coefficients, then analytical solutions are given, so that all the cases are covered. Combined with D4σ-Z-scan method, the third- and fifth-order nonlinear coefficients are measured at 532 nm and 1064 nm in the picosecond regime.

Why optical nonlinear characterization using imaging technique is a better choice

We show that the direct measurement of the beam radius in Z-scan experiments using a CCD camera at the output of a 4f-imaging system allows a higher sensitivity and a better accuracy than Baryscan. One of the advantages is to be insensitive to pointing instability of the pulsed laser because no hard aperture is employed as in the usual Z-scan. In addition, the numerical calculations involved here and the measurement of the beam radius are simplified since we do not measure the transmittance through an aperture and it is not subject to mathematical artifacts related to a normalization process, especially when the diffracted light is very low.