Propagation Of High-power Pulses Research Articles

Post-filamentation propagation of high-power laser pulses in air in the regime of narrowly focused light channels

We report the results of experimental and theoretical studies of the post-filamentation stage of nonlinear propagation of high-power pulsed radiation from a Ti : sapphire laser in air. We have for the first time obtained the experimental dependences of the angular divergence of specific spatially localised high-intensity light structures that are observed in the beam after its multiple filamentation (post-filamentation of channels) when varying the initial focusing of laser radiation and its energy. It is found that the angular divergence of the post-filamentation channels decreases with increasing pulse energy and reducing beam numerical aperture. The experimental dependences are qualitatively interpreted based on the diffraction model of the Bessel – Gaussian beam.

Nonlinear optical response of noble gases via the metastable electronic state approach

The goal of this paper is to elucidate the theoretical underpinnings of the metastable electronic state approach (MESA) and demonstrate its utility for the evaluation of the nonlinear optical response of noble-gas atoms with emphasis on the application of the method to the propagation of multicolor optical fields in large-scale, spatially resolved simulations. More specifically, single-active-electron models of various atoms are employed to calculate their nonlinear properties both within the adiabatic approximation, involving a single metastable state and beyond, capturing inertial effects, and wavelength-dependent ionization. Simulations for excitation pulses at different center wavelengths as well as ionization in two-color pulses are presented and compared with numerical solutions of the time-dependent Schr\odinger equation. Illustrative examples of the numerical simulation of high-power pulse propagation incorporating MESA data are also presented and showcase the successful application to optical filamentation in the midinfrared region.

Relativistic critical density increase and relaxation and high-power pulse propagation

High-power laser pulse propagation in an overdense plasma due to the relativistic critical density increase has been investigated in one dimension. In a first step the conditions for the existence of a relativistic critical density are delimited and supported by particle-in-cell simulations. Its accurate determination is made possible by the installation of a new numerical diagnostics. Guided by this we show that the critical density increase strongly depends on both laser polarization and plasma density profile. Further, we find a new relaxation time ranging from several to many laser cycles, which sets a limit for short laser pulse manipulation and tailoring. Paramountly, it is proved that in the power optics domain the pulse propagation velocity is inhibited by the relativistic energy density in the medium and by the efficient reflection, in contrast to the group velocity from standard dispersion optics.

Experiments on the generation of parabolic pulses in fibers with length-varying normal chromatic dispersion

The experimental results for the propagation of high-power pulses in fibers with length-varying chromatic dispersion are presented.

Focusing limits of ultrashort laser pulses: analytical theory

Simple analytic expressions are derived that describe the propagation of a Gaussian high-power laser pulse subject to ionization defocusing in a gas. The analysis is based on the paraxial-ray equation and the Coulomb-barrier model for optical field ionization. Good agreement with recent experimental data is obtained without an adjustable parameter. Experimental observations relevant to high-power pulse propagation follow naturally from the theory.