Post-filamentation Channels Research Articles

Energy, spectral, and angular properties of post-filamentation channels during propagation in air and condensed media

High-power femtosecond laser pulses undergo large-scale transformations during filamentation in a nonlinear medium. Spatial transformations result in the formation of the post-filamentation channels—intense spatially localized light structures observed in the laser beam at the plasma-free stage of pulse propagation. We present the experimental results on the main characteristics of post-filamentation channels formed by the filamentation of Ti:sapphire laser pulses (744 nm, 90 fs) in air. Angular divergence, spectral composition, power, and temporal parameters of post-filamentation channels at different initial pulse energy are investigated. We study a specific cascade pulse filamentation regime when the post-filamentation channel is initially formed in air and then experiences recurrent filamentation in a condensed medium (fused silica).

Global Self-Focusing and Features of Multiple Filamentation of Radiation of a Subterawatt Ti:Sapphire Laser with a Centimeter Output Aperture Along a 150-m Path

The formation and propagation of postfilamentation channels along a controllable path 150 m long are studied experimentally for collimated beams of different diameters. During multiple filamentation, a laser beam is compressed into a global focus, after passing which its angular divergence is much greater than the divergence of postfilamentation channels generated during the filamentation. It is shown that the intensity of the postfilamentation channels is sufficient for starting multiple filamentation in optical elements at distances much longer than the filamentation region length.

Post-filamentation light channels in air

The results are presented of the experimental study of spatial characteristics of postfilamentation light channels in air formed by femtosecond pulses of a Ti:Sapphire laser with different energy for focused and collimated beams. It is found that the angular divergence of channels is dozens of times lower than the angular divergence of a beam as a whole for focused beams in the far zone from the filamentation region. The angular divergence of the channels first significantly decreases with an increase in the pulse energy and then saturates. For collimated beams, at a fixed distance from the source, an increase in the pulse energy also leads to stabilization of the channel cross section.

Parameters of intense light channels during the postfilamentation stage of ultrashort laser radiation evolution

Results of laboratory and numerical experiments on the multiple filamentation of high-power pulse Ti:Sapphire laser radiation (740 nm) in air are presented. The postfilamentation stage of pulse propagation in the form of intensive spatially localized light structures is investigated. The angular divergence of postfilamentation channels is studied under variation in the initial laser beam focusing. The threshold distance for the refilamentation of postfilamentation channels in a glass plate is measured.

Post-filamentation light channels in air

Post-filamentation light channels in air

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.