Self-compression of optical laser pulses by filamentation

International audienceDuring the propagation of intense femtosecond laser pulses in a transparent medium, pulse shortening can occur without external guiding. Experimental evidence for this effect and a description of its physical origin are presented. Nearly single cycle pulses at 800 nm with an energy of 0.120 mJ can be obtained with excellent beam quality. Carrier envelope offset phase (CEP) stability is conserved or even improved after the nonlinear propagation stage. Prospects for further improvement are discussed

Ab initio calculations of the linear and nonlinear susceptibilities of N2, O2, and air in midinfrared laser pulses

We present first-principles calculations of the linear and nonlinear susceptibilities of N2, O2, and air in the midinfrared (MIR) wavelength regime from 1-4μm. We extract the frequency-dependent susceptibilities from the full time-dependent dipole moment that is calculated using time-dependent density functional theory. We find good agreement with curves derived from experimental results for the linear susceptibility and with measurements for the nonlinear susceptibility up to 2.4μm. We also find that the susceptibilities are insensitive to the laser intensity even in the strong field regime up to 5×1013W/cm2. Our results will allow accurate calculations of the long-distance propagation of intense midinfrared laser pulses in air

Time-resolved refractive index and absorption mapping of light-plasma filaments in water

By means of a quantitative shadowgraphic method, we performed a space-time characterization of the refractive index variation and transient absorption induced by a light-plasma filament generated by a 100 fs laser pulse in water. The formation and evolution of the plasma channel in the proximity of the nonlinear focus were observed with a 23 fs time resolution.Comment: 3 pages, 3 picture

Steep nonlinear global modes in spatially developing media

International audienceA new frequency selection criterion valid in the fully nonlinear regime is presented for extended oscillating states in spatially developing media. The spatial structure and frequency of these modes are dominated by the existence of a sharp front connecting linear to nonlinear regions. A new type of fully nonlinear time harmonic solutions called steep global modes is identified in the context of the supercritical complex Ginzburg-Landau equation with slowly varying coefficients. A similar formulation is likely to be applicable to fully nonlinear synchronized global oscillations in spatially developing free shear flows

Energy deposition dynamics of femtosecond pulses in water

We exploit inverse Raman scattering and solvated electron absorption to perform a quantitative characterization of the energy loss and ionization dynamics in water with tightly focused near-infrared femtosecond pulses. A comparison between experimental data and numerical simulations suggests that the ionization energy of water is 8 eV, rather than the commonly used value of 6.5 eV. We also introduce an equation for the Raman gain valid for ultra-short pulses that validates our experimental procedure.Comment: 4 pages, 5 figures, submitted to Applied Physics Letter

Laser beam self-symmetrization in air in the multifilamentation regime

We show experimental and numerical evidence of spontaneous self-symmetrization of focused laser beams experiencing multi-filamentation in air. The symmetrization effect is observed as the multiple filaments generated prior to focus approach the focal volume. This phenomenon is attributed to the nonlinear interactions amongst the different parts of the beam mediated by the optical Kerr effect, which leads to a symmetric redistribution of the wave vectors even when the beam consists of a bundle of many filaments.Comment: 9 pages, 7 figure

Superfilamentation in air

The interaction between a large number of laser filaments brought together using weak external focusing leads to the emergence of few filamentary structures reminiscent of standard filaments, but carrying a higher intensity. The resulting plasma is measured to be one order of magnitude denser than for short-scale filaments. This new propagation regime is dubbed superfilamentation. Numerical simulations of a nonlinear envelope equation provide good agreement with experiments.Comment: 5 pages, 4 figure