A. M. Kabanov

Kerr-driven nonlinear refractive index of air at 800 and 400 nm measured through femtosecond laser pulse filamentation

The filamentation dynamics of 15 GW femtosecond laser pulses at 800 and 400 nm wavelengths upon their tight focusing in air is studied experimentally. The spatial position and extent of plasma channel formed within the filamentation zone as a function of laser pulse power are investigated. The processing of the experimental data according to the Marburger formula by J. H. Marburger [Prog. Quantum. Electron. 4, 35 (1975)] and the dispersion relations for air cubic nonlinearity has allowed to estimate the effective value of the Kerr-driven air refractive index on 400 nm as 5.36 × 10−19 cm2/W with a 5% error.

Self-action of tightly focused femtosecond laser radiation in air in a filamentation regime: Laboratory and numerical experiments

The influence of self-focusing of strong femtosecond laser radiation on the spatial energy distribution of a laser beam was studied. Experimental data are provided on the transverse energy density distribution of the tightly focused radiation of the Ti-sapphire laser following its filamentation in air. The results are interpreted within the framework of the nonlinear Schrödinger equation model. The best agreement between the theory and the experiment is found in the model that takes into account the change of character of the nonlinear response of the medium induced by high-intensity radiation in the nonlinear focus, which includes the change of the ionization mechanism of molecules from multiphoton ionization to tunnel ionization, the completely instantaneous Kerr nonlinearity, and saturation of the latter due to higher-order nonlinearity. The mechanism of the ionization of molecules can change from purely multiphoton ionization to tunnel ionization.

Broadband emission spectrum dynamics of large water droplets exposed to intense ultrashort laser radiation

We report on experiments on the interaction of a gigawatt femtosecond laser pulse train with hanging isolated millimeter-sized water droplets. A transparent droplet experienced explosive boiling-up and emitted light in the visible spectrum as a result of laser-induced plasma formed inside the droplet volume. The droplet emission spectra showed remarkable broadening, depending on the laser power. The role of pulse self-phase modulation in measured spectral broadening when the pulse propagates through the droplet is discussed.

Filament formation beyond linear focus during femtosecond laser pulse propagation in air

The threshold relation between the strength of laser beam focusing and its peak power is determined for post-focal filamentation on the basis of the experimental data and numerical simulations. The dynamics of the post-focal filamentation can vary (propagating or reconstruction type) depending on the strength of linear beam focusing.

Filamentation of a sharply focused ultrashort laser pulse at wavelengths of 800 and 400 nm: Measurements of the nonlinear index of air refraction

We present the results of experimental investigations of the filamentation dynamics of high-power ultrashort Ti:Sapphire-laser pulses with wavelengths of 800 and 400 nm with their sharp focusing in air. The dependences of position and dimensions of a plasma channel generated in the nonlinear beam focus zone on the laser pulse power are obtained. The effective value of the nonlinear index of air refraction related to the optical Kerr effect is determined for two laser wavelengths from processing of the dependences when using laser radiation self-focusing theory.

Filamentation of the focused Ti: Sapphire laser pulse in air at two harmonics

The results of experiments on the filamentation dynamics of high-power ultrashort Ti: sapphire laser pulses with wavelengths of 800 and 400 nm upon their sharp focusing in air are presented. The dependences of the position and dimensions of the plasma channel that forms in the region of the nonlinear beam focus on the laser pulse power are obtained. The spectra of the laser pulse during its filamentation are measured.

Angular diagram of broadband emission of millimeter-sized water droplets exposed to gigawatt femtosecond laser pulses

We report on the experiments on the interaction of gigawatt femtosecond laser pulses with suspended millimeter-sized water droplets. The transparent droplets experienced laser-induced breakdown and explosive boiling up and emitted a broadband radiation. This radiation covers the spectral range from 450 to 1100 nm and consists of the spectrum of laser pulse scattered and transformed by the droplet due to self-phase modulation and plasma emission produced in water during photoionization. The droplet emission spectrum showed remarkable broadening at all viewing angles and is maximal in the direction of the laser exit from the droplet. The enlargement of the droplet results in additional spectral spreading of the emitted radiation. The depth and amount of laser pulse spectral self-transformations upon propagation through the water droplet are simulated by means of numerical calculations.

Interaction between gigawatt laser pulses and liquid media: Part 1. Explosive boiling of large individual water droplets

The results of experiments on femtosecond GW laser pulse interaction with isolated millimeter-size water droplets are presented. The temporal and spatial dynamics of optical breakdown in a liquid particle is investigated. The mechanical fragmentation of the droplet as a result of the evaporation and explosion of superheated areas is also discussed. The spectral characteristics of water particle glow during its explosive boiling are investigated.

Propagation of a high-power ultrashort laser pulse along a horizontal atmospheric path

Experimental results of the study of the evolution of the spatial profile and frequency spectrum of terawatt ultrashort Ti: Sa laser pulses propagating along atmospheric paths in the self-focusing mode are presented. The dependence of the laser radiation energy characteristics at the receiving plane on its initial peak power is determined. The tendency of an increase of the laser beam’s angular size and spectral width when increasing its output power is stated. The obtained regularities have been interpreted qualitatively and quantitatively based on the numerical calculations performed in the framework of the model of the nonstationary self-action of an ultrashort light pulse in air. The ob tained results are compared to the results of the authors’ earlier laboratory experiments on the filamentation of focused laser femtosecond radiation.

Multiple filamentation of collimated laser radiation in water and glass

Results of an experimental study of spatial parameters of the region of multiple filamentation of gigaand terawatt pulses of a Ti:Sapphire laser in glass and water are described. The pulse-power dependencies of the coordinates of the filamentation region, the number of filaments, their distribution along the laser beam axis, and the mean length of the filaments are presented. It is shown that the spatial parameters of the filamentation region are qualitatively similar in water and glass. It is found that the number of filaments along the region of multiple filamentation is a unimodal distribution. When increasing the radiation power, the length of individual filaments in the region of multiple filamentation is reduced, and their diameters are quasi-constant at all power values implemented in the experiment. When attaining a certain power of laser pulses with a Gaussian energy-density distribution, the filamentation region takes the shape of a hollow cone with the apex directed to the radiation source.