Nonlinear Propagation and Filamentation on 100 Meter Air Path of Femtosecond Beam Partitioned by Wire Mesh

Abstract

High-intensity (∼1 TW/cm2 and higher) region formed in the propagation of ∼60 GW, 90 fs Ti:Sapphire laser pulse on a ∼100 m path in air spans for several tens of meters and includes a plasma filament and a postfilament light channel. The intensity in this extended region is high enough to generate an infrared supercontinuum wing and to initiate laser-induced discharge in the gap between the electrodes. In the experiment and simulations, we delay the high-intensity region along the propagation direction by inserting metal-wire meshes with square cells at the laser system output. We identify the presence of a high-intensity region from the clean-spatial-mode distributions, appearance of the infrared supercontinuum wing, and occurrence of the laser-induced discharge. In the case of free propagation (without any meshes), the onset of the high-intensity zone is at 40–52 m from the laser system output with ∼30 m extension. Insertion of the mesh with 3 mm cells delays the beginning of the high-intensity region to 49–68 m with the same ∼30 m extension. A decrease in the cell size to 1 mm leads to both delay and shrinking of the high-intensity zone to 71–73 m and 6 m, respectively. Three-dimensional simulations in space confirm the mesh-induced delay of the high-intensity zone as the cell size decreases.

Filamentation of high-power femtosecond laser pulses with full and partial amplitude modulation by a mesh mask

“…An increase in the coordinate of the filamentation beginning and a decrease in its length (Fig. 2) are consistent with the results of numerical and experimental studies obtained in [11].…”

“…Formalism of its solving is presented in detail in [12]. The adequacy of the description of the nonlinear propagation of high-power femtosecond laser radiation in the regime of laser plasma generation and filamentation using the reduced 3D NLSE was discussed earlier, for example [11,12]. In the same place, a comparison was made of the simulation results obtained on the basis of solving the full (3D + 1) and reduced 3D NLSE models, which showed their good agreement.…”

“…In this regard, the most reliable and simplest method in terms of technical implementation is using of structured laser radiation, spatially modulated by amplitude masks. In this case, various apertures (round, rectangular) [7,8] or mesh masks [9][10][11] can act as modulating elements. Thus, in [11], when varying the mesh mask cell sizes, it was shown that the coordinate of the beginning of filamentation shifts (by about 25%) from the radiation source while maintaining its length (compared to the case when the mesh was not used) and also that the origin coordinate can increase by a factor of 2 with a decrease in the filamentation length.…”

“…In this case, various apertures (round, rectangular) [7,8] or mesh masks [9][10][11] can act as modulating elements. Thus, in [11], when varying the mesh mask cell sizes, it was shown that the coordinate of the beginning of filamentation shifts (by about 25%) from the radiation source while maintaining its length (compared to the case when the mesh was not used) and also that the origin coordinate can increase by a factor of 2 with a decrease in the filamentation length. This case is most interesting for problems of atmospheric optics, when radiation propagates along extended paths, and the shift of the filamentation start coordinate from the radiation source is more significant, rather than its length.…”