X-ray spectra from laser targets in experiments on the SOKOL-P facility

X-ray spectra from targets irradiated by picosecond laser pulses with intensities of 3 × 10¹⁷-10¹⁸ W/cm² have been studied experimentally on the SOKOL-P facility. Both massive metal targets and multilayer targets with a buried emitting layer have been examined. The measurement results are interpreted by using numerical simulations and theoretical analysis. Experimental data on the X-ray continuum in the photon energy range of 0.8–6 keV and the line spectra of hydrogen-and helium-like aluminum ions are found to agree satis-factorily with numerical results.     

Monoenergetic proton beams from mass-limited targets irradiated by ultrashort laser pulses

Results are presented from three-dimensional numerical simulations carried out to study different regimes of proton acceleration from plane targets (such as double- and single-layer foils, homogeneous foils of light and heavy ions, and mass-limited targets) irradiated by laser pulses of moderate intensity. It is shown that, in the interaction of a laser pulse having an energy of about 20 J with mass-limited targets consisting of heavy ions and protons, it is possible to generate a monoenergetic proton beam with an energy of about 150 MeV.     

Investigation of the angular distribution and energy spectrum of fast ions produced during irradiation of targets by short laser pulses in the SOKOL-P facility

Results are presented from experimental investigations of the angular distributions and energy spectra of fast ions produced in deuterium polyethylene targets under irradiation by picosecond laser pulses with intensities of up to 2 × 10¹⁸ W/cm² in the SOKOL-P facility. The parameters of ion fluxes were measured by time-of-flight spectrometers based on semiconductor detectors.     

Experimental and theoretical studies of the physical processes occurring in thin plane targets irradiated by intense X-ray pulses

Results are presented from experimental and theoretical studies of the interaction of intense X-ray pulses with different types of plane targets, including low-density (～10 mg/cm³) ones, in the Angara-5-1 facility. It is found experimentally that a dense low-temperature plasma forms on the target surface before the arrival of the main heating X-ray pulse. It is demonstrated that the contrast of the X-ray pulse can be increased by placing a thin organic film between the target and the discharge gap. The expansion velocity of the plasma created on the target surface irradiated by Z-pinch-produced X rays was found to be (3–4) × 10⁶ cm/s. A comparison between the simulation and experimental results confirms the validity of the physical-mathematical model used.     

Diagnostics of jet structures formed in the plasma corona during the irradiation of porous targets by intense laser pulses

Jet structures formed during laser irradiation of porous targets with an average density of ?? = 1?30 mg/cm³ were studied experimentally by using the diagnostic complex of the Mishen facility. To study complicated plasma structures, the experimental data were processed using specially elaborated mathematical methods. The probability of the emergence of jet plasma structures in plane open-pore triacetate cellulose targets was studied as a function of the parameter ??d, where ?? is the average mass density and d is the target thickness. Analysis of the experimental results and their comparison with the existing data on the jet structures formed during laser irradiation of solid-density targets allowed the authors to reveal the characteristic features and mechanisms of the development of large-scale plasma jets.     

Collisional electron heating by an ultraintense ultrashort laser pulse focused in a gas

Collisional heating of plasma electrons in the field of an ultraintense ultrashort laser pulse is studied. The numerical results obtained by the method of molecular dynamics are compared with the well-known results from kinetic simulations. A model is proposed that provides a good agreement with the results of calculations for both linearly and circularly polarized high-intensity laser pulses.     

High-energy ion generation by short laser pulses

This paper reviews the many recent advances at the Center for Ultrafast Optical Science (CUOS) at the University of Michigan in multi-MeV ion beam generation from the interaction of short laser pulses focused onto thin foil targets at intensities ranging from 10¹⁷ to 10¹⁹ W/cm². Ion beam characteristics were studied by changing the laser intensity, laser wavelength, target material, and by depositing a well-absorbed coating. We manipulated the proton beam divergence using shaped targets and observed nuclear transformation induced by high-energy protons and deuterons. Qualitative theoretical approaches and fully relativistic two-dimensional particle-in-cell simulations modeled energetic ion generation. Comparison with experiments sheds light on ion energy spectra for multi-species plasma, the dependences of ion-energy on preplasma scale length and solid density plasma thickness, and laser-triggered isotope yield. Theoretical predictions are also made with the aim of studying ion generation for high-power lasers with the energies expected in the near future, and for the relativistic intensity table-top laser, a prototype of which is already in operation at CUOS in the limits of several-cycle pulse duration and a single-wavelength spot size.     

In-vivo intratissue ablation by nanojoule near-infrared femtosecond laser pulses

Non-invasive intratissue ablation was performed in the cornea of living rabbits by using 80 MHz near-infrared intense nanojoule femtosecond laser pulses. The intratissue surgical effect was induced by multiphoton absorption at a wavelength of 800 nm and was ascertained by histological examination. Highly precise intratissue ablation was obtained with no detrimental effects to the overlying or underlying layers. Activated keratocytes in the laser-treated corneas were detected with two-photon imaging postoperatively. Intratissue femtosecond laser ablation thus has potential as a effective technique in refractive surgery for the treatment of visual disorders. This work was supported in part by the German Science Foundation.     

Generation of terahertz radiation from a low-density plasma slab irradiated by a laser pulse

The generation of terahertz electromagnetic radiation when a laser pulse propagates through a low-density plasma slab is considered. It is shown that terahertz waves are excited because of the growth of a weakly damped, antisymmetric leaking mode of the plasma slab. The spectral, angular, and energy parameters of the terahertz radiation are investigated, as well as the spatiotemporal structure of the emitted waves. It is demonstrated that terahertz electromagnetic wave fields are generated most efficiently when the pulse length is comparable to the slab thickness.     

Interaction of plasma clouds produced from two laser targets

Results are presented from studies of the interaction of two plasma clouds produced from two different-type laser targets in an ambient gas in the MKV-4 stand of the Iskra-5 facility. The experimental data are compared with the results of numerical simulations.     

Electron acceleration by Langmuir waves excited by a laser pulse in a semi-infinite plasma

Results are presented from a theoretical investigation of the acceleration of test electrons by a Langmuir wave excited by a short laser pulse at half the electron plasma frequency. Such a pulse penetrates into the plasma over a distance equal to the skin depth and efficiently excites Langmuir waves in the resonant interaction at the second harmonic of the laser frequency. It is shown that the beam of electrons accelerated by these waves is modulated into a train of electron bunches, but because of the initial thermal spread of the accelerated electrons, the bunches widen and begin to overlap, with the result that, at large distances, the electron beam becomes unmodulated.     

Measurements of plasma temperature in indirect drive targets from the shock wave velocity in aluminum in the Iskra-5 facility

Results are presented from the development of a method for measuring plasma temperature in indirect (X-ray) drive targets by recording the shock wave velocity in the Iskra-5 facility. The samples under investigation were irradiated by X-rays in a converter box, and the shock wave velocity was determined from the time at which the wave reached the back surface of the sample and the surface began to emit visible radiation. This emission, in turn, was detected by a streak camera. The results of experiments on the interaction of X radiation with a hot dense plasma, as well as the accompanying gas-dynamic processes in aluminum samples, are analyzed both theoretically and numerically. In experiments with Al and Pb samples, the shock wave velocity was measured to vary in the range U = 8–35 km/s, and the range of variation of the temperature of the box walls was measured to be T _e = 140–170 eV.     

Stochastic electron acceleration in plasma waves driven by a high-power subpicosecond laser pulse

The mechanism of stochastic electron acceleration and heating by a picosecond laser pulse in underdense plasma is studied using particle-in-cell simulations and theoretical models. The formation of wide electron energy spectra in the simultaneously acting laser and plasma fields is analyzed. It is shown that electron scattering by turbulent plasma fluctuations excited through stimulated forward Raman scattering plays a governing role in the formation of high-energy tails in the electron distribution function.     

Possibility of deexcitation of isomeric nuclei in plasmas produced by subpicosecond laser pulses

Possible schemes of X-ray-activated deexcitation of isomers of rhodium, silver, tellurium, and bismuth are considered. It is shown that conditions necessary for deexcitation of rhodium isomer can, in principle, be achieved in a high-temperature solid-body-density plasma produced by an ultrashort laser pulse.     

Efficiency of ion acceleration by a relativistically strong laser pulse in an underdense plasma

A particle-in-cell simulation is used to investigate ion acceleration by a femtosecond laser pulse propagating in an underdense plasma slab. In plasma slabs with different thicknesses, the ions are found to be accelerated by different mechanisms. It is shown that, for laser pulse intensities in the range (5–10)×10¹⁹ W/cm², the ions are accelerated near the plasma-vacuum interface. __________ Translated from Fizika Plazmy, Vol. 27, No. 3, 2001, pp. 225–234. Original Russian Text Copyright ￠ 2001 by Kuznetsov, Esirkepov, Kamenets, Bulanov.     

Generation of strong magnetic fields by counterpropagating moderate-intensity laser pulses in a low-density plasma

A study is made of the generation of strong quasistatic magnetic fields by counterpropagating moderate-intensity laser pulses of different frequencies in a low-density plasma. Strong magnetic fields are generated by small-scale large-amplitude plasma waves excited at different frequencies by ponderomotive forces in the interaction region of laser pulses. It is shown that magnetic fields are generated most efficiently under resonance conditions such that the frequency difference between laser pulses coincides with the plasma frequency. The spatial distribution of quasistatic magnetic fields is investigated, and the pattern of the contour lines of the electric current is calculated.     

Studies of the optical properties of laser plasmas produced by irradiating spherical targets

Results are presented from studies of the spectral characteristics of a glowing plasma object that forms behind a shock wave propagating in a background gas at a pressure of 1 Torr after laser irradiation of a spherical organic target in the MKV-4 device (a component of the Iskra-5 facility). The experimental data are compared to the results of calculations.