Study of laser induced plasma grating dynamics in gases

Abstract

International audienceThe relaxation of a plasma grating resulting from the interference of two crossing laser filaments in molecular and atomic gases is studied experimentally. Dissipation of the grating fringes is dominated by ambipolar diffusion in atomic gases and by a combination of ambipolar diffusion and collision-assisted free electron recombination in molecular gases. A theoretical model of the grating evolution is developed and compared to experimental results. Good agreement with simulations allows extracting plasma properties such as electron density, diffusion and recombination coefficients in Ne, Ar, Kr, Xe, N_2 , O_2 , CO_2 and air at atmospheric pressure

Long-Lived Refractive-Index Changes Induced by Femtosecond Ionization in Gas-Filled Single-Ring Photonic-Crystal Fibers

“…The plateau in probe phase at t  45 ns can be attributed to the interplay of two effects. Firstly, electron recombination within ~1030 ns [10][11][12], resulting in a gradual increase in refractive index (ionized argon has the longest recombination time of all the noble gases). And secondly, heating due to recombination, which induces a local overpressure proportional to N e [13].…”

Spatio-temporal measurement of ionization-induced modal index changes in gas-filled PCF by prism-assisted side-coupling

“…After the gas has been ionized, gradual free electron recombination (in argon this typically takes several ns [19]) releases energy, which is mostly converted into kinetic energy. This results in local changes in gas density that evolve in time and space until the gas eventually thermalizes over tens of microseconds [3,4,6].…”

Handling beam propagation in air for nearly 10-fs laser damage experiments

“…For that calculation, we consider that the spectral shift (Δλ ¼ λ peak -λ 0 ) is completed with a constant rate of variation (not depending on the instantaneous intensity) and a length of the ionized plasma equal to the confocal parameter (2 z R , where z R ∼190 mm is the Rayleigh length which was measured in this experiment). We also do not consider electron recombination because it occurs on a much longer time than the pulse duration [41] and we assume that the initial value of the index of refraction of air is equal to unity. We finally obtain: n n e c z c R 0 ≈ τ λ λ Δ .…”