ИСТИНА

We present comprehensive experimental and theoretical study of energy deposition in filaments created by regularized multi filamentation of loosely focused femtosecond laser beam containing ~20 critical powers. Filament structure regularization was achieved by applying amplitude or phase masks onto the beam. Different types of phase masks were studied forming high order Hermitte -Gauss beams, as well as other type of diffractive optical elements. Acoustic, spectroscopic and band imaging techniques were employed. We showed that the energy density inside a filament can be easily estimated using acoustic detection. Even in the case of single filament formation from a bundle of converging filaments this technique distinguishes between normal filament and superfilament having much higher energy density in the plasma channel with non-linear scaling on the number of initial filaments. We traced superfilament dynamics along the beam path and estimated superfilament length. Additionally, spectroscopic studies were fulfilled to access superfilament nonlinearity. The experimental data was supported by extensive numerical modeling within 3D+ time axially symmetric simulations with consideration of the fast oscillating carrier wave.