The diffraction-ray model of single filamentation of femtosecond laser pulses for estimating characteristics of the multiple filamentation domain in air

The characteristics of the domain of multiple filamentation of femtosecond laser pulses in air were estimated based on the single filamentation model. As the single filamentation model, the diffraction-ray model is considered. It is based on the representation of a laser beam as a set of diffraction-ray tubes nested in each other that do not intersect in space and do not exchange energy with each other. In this situation changes in tubes shape and cross section during propagation demonstrate the effect of physical processes that occur with radiation in the medium. It is shown that the use of this model for interpreting experimental results and predicting effects is effective. In particular, it was demonstrated that the radius of small-scale intensity inhomogeneities in the profile of a centimeter laser beam, forming the domain of multiple filamentation of subterawatt femtosecond laser pulses, is several millimeters. The power in these inhomogeneities varies from several units to several tens of gigawatts. Telescoping the initial laser beam, leading to an increase in its radius, also expands the sizes of the initial small-scale intensity inhomogeneities and reduces the power contained in them. As a result of this, the coordinate of the filamentation beginning shifts along the path from the source of laser pulses. As the peak power in the beam increases, the length of the filaments and their number increase.

Multiple Filamentation Effects on THz Radiation Pattern from Laser Plasma in Air

An experimental study of few filaments interaction impact on the terahertz radiation pattern has demonstrated that interaction of two close propagating beams leads to formation of a superfilament-like structure with on-axis terahertz yield. Mutual delay between two beamlets tilts the output intensity front of THz emission.

The Laser Lightning Rod project

Lightning is highly destructive due to its high power density and unpredictable character. Directing lightning away would allow to protect sensitive sites from its direct and indirect impacts (electromagnetic perturbations). Up to now, lasers have been unable to guide lightning efficiently since they were not offering simultaneously terawatt peak powers and kHz repetition rates. In the framework of the Laser Lightning Rod project, we develop a laser system for lightning control, with J-range pulses of 1 ps duration at 1 kHz. The project aims at investigate its propagation in the multiple filamentation regime and its ability to control high-voltage discharges. In particular, a field campaign at the Säntis mountain will assess the laser ability to trigger upward lightning.