Andrei B. Savel'ev

Few-cycle optical pulse production from collimated femtosecond laser beam filamentation

A scheme for stable shot-to-shot few-cycle pulse production has been realized by launching an initially collimated laser beam into a gas tube. We found that the optimum parameters for the sevenfold compression of 55 fs, 5 mJ, Ti:Sapphire laser pulses are the following: 0.8-0.9 atm argon gas pressure and the registration aperture with a diameter of 300-700 μm. A technique for the efficient extraction of the self-compressed pulse from the desired position along the filament has been provided by moving the registration aperture along the tube. With this technique, pulses as short as 8 fs were detected at a distance of 1 m from the filament starting position, in agreement with numerical simulations performed using a 3D+time axially symmetric code.

Spectral “soliton” transformation and four-wave mixing under femtosecond laser radiation filamentation in molecular gases

Filaments created during propagation of an ultrashort laser pulses in gases and solids combine high non-linearity with huge intensity and long interaction path. Four-wave mixing, coherent Raman scattering, third harmonic production and others non-linear processes were observed [1, 2]. These studies were made with focused laser beams, when interaction length depends on the Rayleigh length. In this paper we report on thorough investigation of new spectral components formation under filamentation of pre-collimated laser beam in molecular gases. These components arose at the red and blue sides of the initial spectrum and were attributed to the generation of vibrational Raman “spectral solitons” and their cascaded four-wave mixing.

On the origin of fast multi-charged ions from femtosecond laser plasma at moderate intensities

Experimental and numerical investigations of femtosecond laser plasma at the cleaned surface of crystalline Si and w targets are carried out. The constructed picture of ionization, acceleration and recombination of ions in plasma well explains main features of atomic, charge and energy spectra of fast and slow ions.