Vyacheslav M. Gordienko

Excitation and decay of low-lying nuclear states in a dense plasma produced by a subpicosecond laser pulse

The excitation of low-lying nuclear levels in a hot, dense plasma, produced by a subpicosecond pulse with intensity exceeding 1016 W/cm2, is investigated theoretically and experimentally. The basic channels of electronic (inelastic scattering and inverse internal electron convergence) and photon (photoexcitation) excitations of such states as well as the influence of the broadening of a nuclear level on the excitation efficiency and the presence of hot electronic component are examined. The experimental data from measurements of the decay kinetics of the low-lying nuclear level 6.238 keV of the stable isotope 181Ta, which were obtained on two experimental laser systems, are presented.

Neutron generation in dense femtosecond laser plasma of a structured solid target

We report neutron production by the 2H(d, n)3He reaction induced upon the illumination of a solid nanostructured target by femtosecond laser pulses of intensity 20 PW/cm2 (1 PW = 1015 W). The target was structured through the preliminary illumination by a laser pulse of the same intensity.

Generation of High-Energy Negative Hydrogen Ions upon the Interaction of Superintense Femtosecond Laser Radiation with a Solid Target

The formation of a high-energy (∼35 keV) beam of negative hydrogen ions was observed in the expanding femtosecond laser plasma produced at the surface of a solid target by radiation with an intensity of up to 2× 1016 W/cm2. The energy spectra of the H+ and H−-ions show a high degree of correlation.

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.

Evolution of a femtosecond laser-induced plasma and energy transfer processes in a SiO2 microvolume detected by the third harmonic generation technique

A nonlinear optical method has been proposed for probing the evolution of a plasma and energy transfer processes in the microvolume of a transparent dielectric using the third-harmonic probe signal. The electron self-trapping time has been estimated as t = 150 ± 80 fs. A decrease in the third-harmonic probe signal has been detected at the picosecond time scale; this decrease can be attributed to a change in the third-order susceptibility χ(3) of a fused silica sample modified by laser radiation.

Overheated plasma at the surface of a target with a periodic structure induced by femtosecond laser radiation

A periodic structure is induced at the surface of a metal target exposed to a series of p-polarized 200-femtosecond laser pulses with intensity close to the melting threshold of the target material. The period of the structure is determined by the interference between the incident pump wave and the surface electromagnetic wave. Exposure of the obtained structure to the same laser pulse, but with an intensity of ∼1016 W/cm2, provides resonant excitation of the surface electromagnetic waves at the plasma-vacuum interface. This leads to an increase in the X-ray output and the temperature of plasma hot electrons.

Excitation of nuclei in a hot, dense plasma: Feasibility of experiments with 201Hg

It is shown that in a plasma produced on the surface of a sample consisting of a natural mixture of mercury isotopes, ∼104−105201Hg nuclei can be excited into the low-lying isomeric level 1/2− (1.561 keV) by an ultrashort laser pulse with energy ≈1 J, duration ≈200 fs, and intensity ≈1016 W/cm2 and the lifetime of the level can be determined. Possible mechanisms leading to the excitation of 201Hg nuclei by photons and electrons in a dense, hot plasma are examined and the cross sections of the processes are estimated. Schemes for detecting the effect are proposed.

Self-compression of terawatt level picosecond 10 μm laser pulses in NaCl

We propose and numerically validate a self-compression regime of powerful 10??m laser radiation (power 500?GW, energy 1.5?J, pulse duration 2.5?ps) in a NaCl crystal, taking into account its nonlinear and dispersive properties. We demonstrate numerically that the proposed scheme?a solid state compressor containing four NaCl plates (total thickness 19?cm) and divided by spatial filters?avoids the small-scale self-focusing process and reduces by an order of magnitude the initial pulse duration, from 2.5?ps up to 250?fs (seven periods of oscillation) and increases output power from 0.5?TW up to 2.2?TW.

Laser control of filament-induced shock wave in water

We discovered that tight focusing of Cr:forsterite femtosecond laser radiation in water provides the unique opportunity of long filament generation. The filament becomes a source of numerous spherical shock waves whose radius tends to saturate with the increase of energy. These overlapping waves create a contrast cylindrical shock wave. The laser-induced shock wave parameters such as shape, amplitude and speed can be effectively controlled by varying energy and focusing geometry of the femtosecond pulse. Aberrations added to the optical scheme lead to multiple dotted plasma sources for shock wave formation, spaced along the optical axis. Increasing the laser energy launches filaments at each dot that enhance the length of the entire filament and as a result, the shock impact on the material.

Ionization-assisted guided-wave pulse compression to extreme peak powers and single-cycle pulse widths in the mid-infrared

Ionization-assisted spectral broadening of high-energy 10.6 μm laser pulses in a gas-filled hollow waveguide is shown to yield single-cycle pulses with multiterawatt peak powers in the mid-IR. While the highest quality of pulse compression is achieved in the regime of weak ionization, careful management of complex ionization-assisted spectral broadening of guided-wave fields is the key to compressing the output of advanced high-power mid-IR laser sources to single-cycle pulse widths.