The work presents the results on the influence of the temperature of a turbulent layer on the transverse energy structure of femtosecond (multi-ring and Gaussian) laser beams. Gaussian and multi-ring beam profiles exhibit a monotonous growth in the number of intense light maxima with increasing the strength turbulence of air jet and increasing laser pulse energy. The formed intense light channels (~ 1011 W/cm2) make it possible to excite two-photon fluorescence of dyes with a signal level that makes it possible to take at a distance of 100 m.
We present the results of the turbulent layer influence on the characteristics of the filamentation domain at the path beginning for the beams with a diameter of 2.5 and 5 cm. Addition of turbulence results in the fact that the beginning of the multiple filamentation domain (MFD) to the source coming closer. Decreasing of the distance to the beginning and end of the MFR in the presence of turbulence is inappreciable (<10%). The turbulent layer formed at the beginning of the path leads to a multiple increase in the number of the intense channels (~ 1011-1012 W/cm2) with a length >100 m.
The experimental results of the features of formation and path propagation of high-intensity light channels under conditions of distortions of the initial profile of a high-power femtosecond laser beam are presented. The distortions are introduced by amplitude modulation of the laser beam with the help of the masks. The use of amplitude masks allows generation of a given number of high-intensity light channels and their controllable filamentation mainly at short (tens of meters) distances of radiation propagation in air.
The work presents the results of laboratory experiments on controlling the filamentation domain of a focused femtosecond laser beam with a spatially structured (using a deformable mirror) wavefront. We studied aberration beams consisting of coherent nested annular subapertures obtained with a specific shape of a deformable mirror determined from theoretical estimates. This makes it possible to create inhomogeneities in distribution of the optical field amplitude during propagation of the laser beam, which can subsequently become seeds for the light filaments formation. This regime of high-power radiation filamentation control does not require compensation for distortions in the initial beam profile, but on the contrary, it is based on the controlled introduction of preliminarily calculated wavefront aberrations.
The results of the experiments on the excitation and detection of two-photon fluorescence of the dyes by the intense light channels generated by controlling the wavefront of the femtosecond laser pulses are presented. Emission of the dyes and the detection of the backward signal were carried out according to the lidar scheme at a distance of 100 m from the source.
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