Viktor T. Platonenko

Single attosecond soft-x-ray pulse generated with a limited laser beam

The problem of obtaining a single attosecond pulse with high-order harmonics generation is considered. A method for producing an exciting light pulse with a time-dependent degree of ellipticity from a one-frequency linearly polarized laser pulse by means of linear optics is suggested. The whole of the field generated with a limited beam of this light in a gas target is calculated in the far zone. For this calculation we use an original method based on the time approach of a theory of high-order harmonic generation. Contrasted and intense (focused) single attosecond soft-x-ray pulses are calculated by suppression of the low-frequency part of the field to as many as 11 harmonics of exciting frequency. The possibility of suppressing the low-frequency part of the field with pinholes is shown.

Generation of an attosecond X-ray pulse in a thin film irradiated by an ultrashort ultrarelativistic laser pulse

The possibility of generating an attosecond x-ray pulse in a thin solid-density plasma layer irradiated by a femtosecond laser pulse of ultrarelativistic intensity has been demonstrated in numerical simulation. Changes in the plasma layer parameters during the light pulse result in the generation of a wide, partly continuous radiation spectrum in the layer. The separation of limited parts in the reflected or transmitted light spectrum makes it possible to obtain isolated short electromagnetic pulses with an intensity reaching 1% of the exciting light intensity.

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.

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.

Toward sub-terrawatt mid-IR (4-5 micrometer) femtosecond hybrid laser system based on parametric seed pulse generation and amplification in Fe2+: ZnSe

For the first time, an experimentally measured seed pulse gain of about 2 cm−1 allows possibilities in the scaling power of such a femtosecond laser system in terawatts. The concept of a subterawatt power level hybrid femtosecond mid-IR (4–5 μm) laser system, based on a weak pulse from an optical parametric mid-IR seeder that is amplified in chalcogenide monocrystalline Fe2+:ZnSe, to gain medium has been proposed and designed. The method and approach for optimizing the choice of nonlinear medium, its length, and the required light intensity for the efficient non-linear self-compression of an ultrashort pulse has also been proposed and considered.

Effective generation of characteristic K-rays from large laser-excited SF6 clusters in the presence of an Ar carrier gas

The parameters of characteristic sulfur Kα-rays generated from SF6 clusters that are surrounded by argon atoms and are irradiated by intense laser radiation have been analyzed. It has been found that the formation of large SF6 clusters under the optimum experimental parameters is accompanied by the high-efficiency generation of the characteristic X rays, and the flux density of the characteristic X-ray photons is 100 photons/(mrad2 pulse) at a laser-pulse energy of 5 mJ. It has been shown that the third-harmonic generation process can be used to characterize the spatial sizes of the gas-cluster jet and the region of the cluster plasma.

Overcritical plasma ignition and diagnostics from oncoming interaction of two color low energy tightly focused femtosecond laser pulses inside fused silica

We report overcritical (3.3 × 1021 cm−3) microplasma produced by low energy colliding IR (infrared) (1.24 μm) and visible (0.62 μm) femtosecond pulses tightly focused (NA = 0.5) into the bulk of fused silica with on-line monitoring based on third harmonic generated by the IR beam. It was established that the absorbed energy density is the key parameter that determines the micromodification formation threshold and in our experimental conditions it is close to 4.5 kJ cm−3. Non-monotonic behavior of the third harmonic signal as a function of time delay between visible (0.62 μm) and IR (1.24 μm) femtosecond pulses demonstrates the qualitative differences about the two phenomena: one is the seed electrons generation by the visible pulse via multiphoton ionization and second is the avalanche ionization by the IR pulse. We predict that the tandem two-color excitation of wide-bandgap dielectric in comparison with single-color pulse interaction regime allows providing a much higher absorbed energy density and overcritical plasma.

Off-axially phase-matched high-order harmonic generation in an extended medium

We investigate theoretically high-order harmonic generation in gases and show that, if the target thickness is high, off-axial phase matching is of importance. Results of a numerical study of harmonic generation that takes into account the self-action of the laser pulse are presented. We show that self-guiding of the laser pulse in a noble gas makes possible off-axially phase-matched high harmonic generation if some easily ionizable gas is added to the main generating gas. In calculations for such mixtures we obtained conversion efficiencies as great as approximately 10-3–10-2 for the 33rd harmonic of a Ti:sapphire laser and approximately 10-4 for the 121st harmonic.

Sub - Picosecond Petawatt Class N2O Laser System: mid-IR Non-linear Optics and New Possibilities for High Energy Physics

Progress on developing a petawatt laser source in 10&mgr;m region is described. Analysis of optical pumping N2O containing active media by pulsed multifrequency HF laser has been performed. It is shown that amplification of ultrashort pulses should be carried out in the gain band centered at 930cm-1. Amplification of seed ultrashort (~1ps) pulses in atmospheric and high pressure N2O (up to 5atm) amplifiers pumped by powerful pulsed HF chemical lasers is theoretically studied. It is shown that N2O atmospheric pressure amplifiers can be effectively used for production output energy of 1kJ. We discuss a simple add for subpicosecond N2O- laser system to generate joule-level 200 fs pulses with high temporal quality and an overall conversion efficiency of 80%. Petawatt class N2O laser could be prospective for strong-field physics applications and production of high energy proton beams upon irradiating gas jets.

Generation of two attosecond pulses with tunable delay using orthogonally-polarized chirped laser pulses

We investigate theoretically the high-order harmonic generation (HHG) by two orthogonally-polarized linearly chirped laser pulses. We show that such generating field has a specific temporal variation of the ellipticity which provides generation of two XUV attosecond pulses with tunable delay between them. This delay is controlled by the delay between the two generating pulses. Perspectives of application of this technique for the attosecond pump - attosecond probe experiments are discussed.