A. A. Shashkov

Excitation of tantalum-181 nuclei in a high-temperature femtosecond laser plasma

The excitation of nuclei in a laser plasma is observed. Gamma rays from the radiative decay of the isomeric level 9/2− (6.238 keV) 181Ta in a high-temperature femtosecond Ta laser plasma are detected.

Self-channeling of femtosecond laser radiation in transparent two-component condensed medium

We have observed self-guiding of a single femtosecond visible laser pulse in the bulk of transparent nonlinear media (SiO2, KDP) and in the water. The dependence of filament length on laser pulse energy was measured. Continuous open-ended channels and frozen modifications of the matter were observed in transparent two-component condensed medium (thin glass plate placed in water).

Plasma channel formation and micromodification of KDP crystal by tightly focused Cr:forsterite femtosecond laser radiation

Experiments on single pulse plasma channel formation in non-linear KDP crystal by tightly focused (NA = 0.47) fundamental and doubled Cr:forsterite laser radiation with energy of 0.1 ÷ 10 μJ and 100 fs pulse duration were carried out. We propose the simple model of non-linear absorption of femtosecond laser radiation in plasma channel. This model allows estimate laser intensity in the channel and plasma parameters.

Plasma channels characteristics dependence on tightly focused femtosecond laser radiation parameters

Tight focusing of femtosecond laser radiation with microjoule pulse energy in non-linear crystal volume (intensity of the order of 10 W/cm2) causes self-focusing, multiphoton ionization of the matter, plasma channel formation, electrons heating, and subsequent micromodification of the structure. The processes threshold, behavior and efficiency strongly depend on such laser pulse parameters as pulse duration, energy and radiation wavelength

Photorefraction in a KDP crystal induced by femtosecond laser radiation

Femtosecond laser radiation self-channeling and second harmonic generation under plasma formation conditions were investigated. Laser pulses with sub- and microjoule energy were tightly focused into the volume of a KDP crystal, Estimated laser pulse intensity was of the order 1013 W/cm2 in the focal spot exceeding damage and plasma ignition thresholds in the crystal. Threshold of plasma channel formation measured in the experiment corresponds to critical power of self-focusing 1.5f0.1 MW for KDP crystal. Plasma channels with length up to 150 μm were observed in the volume of the KDP crystal. We developed an algorithm allowing estimating electron density and temperature in the plasma channel using experimental dependence of laser energy transmittance through the crystal on incident laser energy. For laser pulse energy 1 μJ estimated electronic density in the plasma channel is of the order of l020 cm-3 (that is about one tenth of the critical plasma density value) and mean electronic temperature is about 3 eV. Free plasma electrons leaded to refraction index increasing by 5 %, extinction coefficient was -25 cm-1. The maximum measured efficiency of second harmonic generation was 1.2 %.

Control of femtosecond laser plasma parameters by surface contaminants cleaning with preceding pulse laser

Making use of time-of-flight and mass-spectroscopic methods we investigated influence of the film on the target surface at vacuum of 10-5 Torr onto ions emission from plasma created by femtosecond laser pulse with itensity of 2 • 1016 W/cm2. It was shown that the highest energy per charge (8.5 keV) acquire protons, while basic target ions (Si, Ti) gain less energy. Heating by laser nanosecond pulse advancing femtosecond pulse by 0.1 - 100 ms with energy density up to 20 J/cm2 allows for effective surface cleaning due to removal of molecules containing hydrogen, carbon and oxygen. By the contrast to the instantaneous resistive heating the pulsed laser cleaning provides for higher heating temperatures and can be used for any solid targets in the regimes of thermal and plasma cleaning.

Self-channeling of femtosecond visible laser pulse with microjoule energy and micromodification in transparent target

We have observed self-guiding of a single femtosecond visible laser pulse in the bulk of fused silica. The filament length and diameter versus pulse energy have been measured. Velocity of ions flying out from the plasma channel was determined with the use of time-of-flight measurements. The laser-induced micromodification in the bulk of the fused silica has discrete structure and is close to the filament form.

Overheated femtosecond plasma in highly porous silicon

We present results on plasma formation in porous silicon (cluster like solid with mean cluster size of 3 nm, mean density 0.1 - 0.2 of crystalline silicon) by femtosecond laser pulses at intensity above 10 TW/cm2. We deduced hot electron temperature as high as 8 keV and fast ions of at least 2 MeV energy.

Interaction of Superintense Femtosecond Laser Pulses with Cluster-like Solids

We present results on plasma formation in porous silicon (cluster size 3–5 nm, mean density 0.1–0.5 of crystalline silicon) by femtosecond laser pulses at intensity above 10 TW/cm2