I. G. Koprinkov

Self-compression of high-intensity femtosecond optical pulses and spatiotemporal soliton generation

Self-compression of high-intensity femtosecond pulses has been observed in a number of atomic and molecular gases and solid bulk material. The evolution of the femtosecond pulse parameters during the self-compression has been studied under a variety of experimental conditions. Generation of spatiotemporal solitons has been achieved by the combined action of self-compression and self-focusing.

High-energy conversion efficiency of transient stimulated Raman scattering in methane pumped by the fundamental of a femtosecond Ti:sapphire laser

We studied stimulated Raman scattering in pressurized methane in the highly transient regime pumped by 140-fs 0.7-mJ pulses from a Ti:sapphire (Ti:S) laser tuned at 750 nm. Energy-conversion efficiency of the first Stokes of more than 15% was achieved, with no strong sign of saturation with as much as 40 atm (1atm=760Torr) of Raman gas pressure. To our knowledge, this is the highest conversion efficiency of transient stimulated Raman scattering generated directly from the fundamental of a Ti:S laser.

Self-Shortening of Femtosecond Laser Pulses Propagating in Rare Gas Medium

Self-shortening of high-intensity femtosecond pulses in rare gases Ar and Kr has been found at normal dispersion conditions. The self-shortening results in soliton formation due to the medium nonlinearity higher than the third-order, which is the first experimental observation of such type of soliton. A new compression technique, scalable for high-energy femtosecond pulses, has been achieved based on this phenomenon.

Self-compression of high-intensity femtosecond laser pulses in a low-dispersion regime

Self-compression of high-intensity femtosecond laser pulses and more than an order of magnitude increase of the peak intensity are found in a medium of positive group velocity dispersion based on the lowest order optical processes in the (3+1)-dimensional nonlinear Schrodinger equation. A physical mechanism of the pulse compression and intensity gain in a low-dispersion regime is proposed for the first time. A method of high-intensity femtosecond pulse formation can be developed on this basis.

Interference between stimulated Raman scattering and self-phase modulation in pressurized methane in highly transient femtosecond pump regime

The mutual interference between the transient stimulated Raman scattering and the self-phase modulation was considered a long time ago [Phys. Rev. A 2 (1970) 60]. In this work we have studied experimentally, for the first time to our knowledge, the influence of the transient stimulated Raman scattering on the self-phase modulation, considering single-shot Raman spectra. The stimulated Raman scattering was excited in methane by 140 fs pulses of the fundamental wave of a Ti:sapphire laser. Narrowing of the Stokes spectrum and suppression of the self-phase modulation structure were observed with increasing Raman gain, in agreement with the theoretical predictions. The effect has been observed up to 40 atm of methane pressure.

Generation of Light Bullets

We report for the first experimental generation of complete (3+1) dimensional spatio-temporal soliton, or “light bullet”. This is achieved by propagation of high- intensity femtosecond laser pulses in atomic and molecular gases.

Non-adiabatic semiclassical dressed states

We introduce non-adiabatic semiclassical dressed states for a quantum system interacting with an electromagnetic field of variable amplitude and phase, in the presence of dumping. We also introduce a generalized adiabatic condition that allows one to find a closed-form solution for the dressed states. The influence of non-adiabatic factors on the dressed states due to the amplitude and phase field variations and dumping has been found.

Spatiotemporal Dynamics of High-Intensity Ultrashort Laser Pulses in Strongly Nonlinear Regime

The spatiotemporal dynamics of high-intensity femtosecond laser pulses is studied in strongly nonlinear regime. The physical model is capable to describe ultrashort pulse propagation down to single-cycle regime at presence of ionization of the medium. The ionization contribution to the group velocity dispersion is introduced in the model. The pulse propagation is described by the nonlinear envelope equation. The propagation and material equations are solved self-consistently at realistic physical conditions. We have shown that, at typical laboratory scale distances, the linear processes, more particularly – the dispersion, play a secondary role, while the pulse propagation dynamics is ruled mainly by competitive nonlinear processes in neutrals and plasma.

Generation of Stable (3+1)-dimensional High-intensity Ultrashort Light Pulses

The spatiotemporal dynamics of high‐intensity femtosecond laser pulses is studied within a rigorous physical model. The pulse propagation is described by the nonlinear envelope equation. The propagation and the material equations are solved self‐consistently at realistic physical conditions. Self‐compression of the pulse around single‐cycle regime and dramatic increase of the pulse intensity is found. At certain conditions, the peak intensity, transversal width, time duration, and the spatiotemporal pulse shape remain stable with the propagation of the pulse, resembling a soliton formation process. This, to our knowledge, is the first simulation of high‐intensity ultrashort soliton formation dynamics in the (3+1)‐dimensional case.

Generation of a completely dense femtosecond optical supercontinuum

A completely dense femtosecond optical supercontinuum is observed for the first time. It does not exhibit the oscillation-like frequency structure of the well-known optical supercontinuum generated by self-phase modulation. The newly observed optical supercontinuum is attributed to bremsstrahlung radiation from electrons that tunnel the bound potential under a strong optical field. The basic properties of the dense optical supercontinuum are studied.