Interaction Of High-power Laser Radiation Research Articles

Resonance Interaction of High-Power Laser Radiation with Plasma in a Strong Magnetic Field (a Review)

Resonance Interaction of High-Power Laser Radiation with Plasma in a Strong Magnetic Field (a Review)

Using machine-learning methods for analysing the results of numerical simulation of laser-plasma acceleration of electrons

Using machine-learning methods based on self-organising Kohonen maps, the results of numerical simulation of the acceleration of electrons during the interaction of high-power laser radiation with plasma are analysed and classified. The particle-in-cell (PIC) method is used to simulate the interaction in a wide range of parameters (laser intensity and plasma concentration). For each set of parameters, the spectrum of accelerated electrons is found, based on which the charge, average energy, and relative energy spread of accelerated electrons are calculated. Using the obtained values as input parameters of the map, the classification of various acceleration regimes is performed. The developed scheme can be used to identify the optimal acceleration regimes under more realistic conditions, considering a larger number of parameters.

Parametric Interaction of High-Power Laser Radiation with Plasma in a Strong Magnetic Field

The article deals with interaction of an extraordinary laser wave of high amplitude with inhomogeneous plasma in a strong magnetic field in the vicinity of twice the upper-hybrid frequency. The analysis is carried out by means of numerical simulation based on the particle-in-cell (PIC) method. It is demonstrated that in this case, parametric resonance leads to a substantial heating of electrons. The results of analysis of spectra of the longitudinal field suggest that this kind of heating occurs due to nonlinear interaction of the upper-hybrid plasmons driven by the laser wave with electrostatic modes similar to the Bernstein ones in the linear approximation. The dependence of average energy of electrons gained in the course of heating on their initial temperature is investigated.

Formula for the ionisation rate of an atom or ion in a strong electromagnetic field for numerical simulation

A formula is proposed for calculating the rate of field ionisation of an atom or ion, taking into account both tunnel ionisation and barrier suppression ionisation. Compared with the previous formula proposed in 2018, it more accurately describes the transition region between both ionisations and is determined mainly by two parameters: the ionisation potential of an atom or ion and the amplitude of an external electric field. This makes the presented formula suitable for use in numerical packages simulating the interaction of high-power laser radiation with matter by the particle-in-cell (PIC) method.

Calculation of the temperature field of the material in the thermal model of laser ablation

The mechanisms of laser ablation of materials under the interaction of powerful pulsed laser radiation with a material coated with a thin film system were studied. One of the first models of such interaction of high-power laser radiation with matter was the thermal model. A onetemperature thermal model was used when considering the interaction of laser radiation with dielectrics, and a two-temperature model was used when considering the interaction of laser radiation with metals. When studying the processes of laser ablation within the framework of the thermal model, the method of moments with a special selection of the test function was chosen. Computer simulation was conducted to study the dependence of the surface temperature and the characteristic thermal length on the radiant flux. Variants with both constant and variable optophysical characteristics of the phenomenon were considered. Calculations were performed for different time ranges under different initial conditions. The results of the numerical experiment agree well with the data of other authors.

Interaction of high-power laser radiation with low-density polymer aerogels**Presented at the ECLIM 2016 conference (Moscow, 18 – 23 September 2016).

The interaction of high-power subnanosecond laser pulses with low-density targets of cellulose triacetate polymer is considered. An Nd-glass laser setup provides a focal spot intensity of over 1014 W cm−2. An investigation is made of absorption of laser radiation, laser-to-X-ray energy conversion, spectra of ions emitted from the plasma, transmission of laser radiation through the target and plasma, as well as volume heating of the target material. It is experimentally determined that the laser energy conversion efficiency to X-rays with photon energies of a few Kiloelectronvolts decreases with increasing target material density. With the use of targets of density 10 mg cm−3 this efficiency is two times lower in comparison to 2 mg cm−3 density targets. The duration and amplitude of laser pulses transmitted through the target decreases with increasing column target density (the product of target material density and its thickness). The spectra of ions emitted from low-density target plasmas are recorded using ion collectors positioned at different angles relative to the direction of laser beam propagation as well as a high-resolution Thomson mass spectrometer. The ion flux and ion energies are found to increase with increasing target material density. The peak of the ion energy spectrum is shifted towards higher energies with increasing laser radiation intensity.

Experimental setup for studying processes initiated by the interaction of high-power laser radiation and matter

An experimental setup developed in cooperation between the Institute for Energy Problems of Chemical Physics and the Joint Institute for High Temperatures for studying processes that occur during laser sublimation and for modeling thermophysical and chemical processes in situ at high temperatures in large-scale facilities is described.

A radio-frequency impedance spectroscope for studying interaction of high-power laser radiation with crystals

A radio-frequency impedance spectroscope for studying the interaction of high-power laser radiation with nonlinear optical crystals has been developed. It has been revealed that the shape of the piezoelectric resonance line of a crystal heated with laser radiation is identical under both uniform heating in the absence of laser radiation and nonuniform heating resulting from the action of laser radiation. This allows introduction of the notion of the equivalent crystal temperature characterizing the nonuniform temperature distribution in a crystal exposed to laser radiation.

Effect of the spectral distribution of a chirped pulse on the interaction of the high-power laser radiation with matter

The interaction of high-power picosecond laser radiation with solid targets is experimentally studied for the first time at various spectral distributions of a chirped laser pulse. The interaction of the high-power laser radiation with the target is studied at four regimes of the experimental setup: (i) at a relatively high contrast (103) in the picosecond (Δt ∼ 25 ps) range, (ii) at a relatively low contrast (3 × 101) in the picosecond (Δt ∼ 25 ps) range, (iii) with spectral distortions of the chirped pulse, and (iv) with a strongly modulated spectrum of the chirped pulse. The results obtained reveal a strong dependence of the atomic and nuclear processes in the laser picosecond plasma on the spectral distribution of the chirped laser pulse. The prospects for the application of the spectral interferometry of chirped pulses for the online control of the parameters of the high-power laser radiation are demonstrated.

Ion Acceleration in a Dipole Vortex in a Laser Plasma Corona

Particle-in-cell simulations show that the inhomogeneity scale of the plasma produced in the interaction of high-power laser radiation with gas targets is of fundamental importance for ion acceleration. In a plasma slab with sharp boundaries, the quasistatic magnetic field and the associated electron vortex structure produced by fast electron beams both expand along the slab boundary in a direction perpendicular to the plasma density gradient, forming an extended region with a quasistatic electric field, in which the ions are accelerated. In a plasma with a smooth density distribution, the dipole magnetic field can propagate toward the lower plasma density in the propagation direction of the laser pulse. In this case, the electron density in an electric current filament at the axis of the magnetic dipole decreases to values at which the charge quasineutrality condition fails to hold. In electric fields generated by this process, the ions are accelerated to energies substantially higher than those characteristic of plasma configurations with sharp boundaries.

Feasibility of using laser ion accelerators in proton therapy

The feasibility of using laser plasma as a source of high-energy ions for the purposes of proton therapy is discussed. The proposal is based on the efficient ion acceleration observed in recent laboratory and numerical experiments on the interaction of high-power laser radiation with gaseous and solid targets. The specific dependence of proton energy losses in biological tissues (the Bragg peak) promotes the solution of one of the main problems of radiation therapy, namely, the irradiation of a malignant tumor with a sufficiently strong and homogeneous dose, ensuring that the irradiation of the surrounding healthy tissues and organs is minimal. In the scheme proposed, a beam of fast ions accelerated by a laser pulse can be integrated in the installations intended for proton therapy.

Resonant fluorescence spectra of a multilevel system in intense radiation and external magnetic fields

Theory and methods of computer simulations permit investigation of the interaction of high-power laser radiation, up to GW/cm2, with atoms having both small and large fine-structure intervals compared with interactions with a laser field and an external magnetic field. The modifications of the energies and population of atomic levels due to such interactions lead to nonlinear effects. Besides modifications in the Raman effect and new effects of rotation of the plane of polarization and circular dichroism that were investigated earlier, there are such nonlinear effects as the modification of the number, positions, intensities, and polarizations of the lines in the resonant fluorescence spectrum. Numerical experiments permit investigation of the characteristics of resonant fluorescence and comparison with known experimental results.PACS Nos.: 32.50, 78.20.L, 42.65, 42.50.H

Estimates of electron-positron pair production in the interaction of high-power laser radiation with high-Z targets

Electron-positron pairs' generation occuring in the interaction of $10^{18}$-$10^{20}$~W/cm$^2$ laser radiation with high-Z targets are examined. Computational results are presented for the pair production and the positron yield from the target with allowance for the contribution of pair production processes due to electrons and bremsstrahlung photons. Monte-Carlo simulations using the PRIZMA code confirm the estimates obtained. The possible positron yield from high-Z targets irradiated by picosecond lasers of power $10^2$-$10^3$~TW is estimated to be $10^9$-$10^{11}$.

Influence of an external pressure and of the type of gas on the mechanism and rate of breakdown of metals by Nd:YAG laser pulses

A study was made of the interaction of high-power laser radiation with metal (W, Fe, Tl, stainless steel) surfaces at high external pressures of inert (Ar) and active (O2) gases. A study was made of the rate of breakdown of stainless steel samples when the power density of the laser pulses was 0.5–10 MW cm-2 and the external pressures ranged from 0.1 Torr to 15 bar. Considerable differences were observed between the rates of breakdown in gases of different nature. A study was made of the dynamics of changes in the profiles of high-power laser pulses reflected from the surfaces of W, Fe, and Ti.

X-ray image-converter streak diagnostics of laser plasmas

A review is given of the developments in dynamic tests on x-ray streak (image-converter) cameras designed for diagnostics of soft x-ray radiation emitted by laser plasmas. A description is given of the procedures used in the application of these cameras in experimental studies of the interaction of high-power laser radiation with matter. Methods for recording x-ray radiation from laser plasmas using plastic scintillators are presented. Special attention is given to the characteristics of x-ray photocathodes such as the energy distribution of photoelectrons, and the thickness and spectral dependences of the quantum efficiency. An account is given of diagnostic experiments on plasmas formed by subpicosecond laser pulses.

Absorption and scattering of laser radiation of different wavelengths by plasma

A numerical investigation was made of the interaction of high-power laser radiation with a plasma, taking into account classical, resonant, and anomalous absorption mechanisms, as well as stimulated Brillouin scattering and specular reflection. The proposed model ensures a qualitative and quantitative agreement of the reflection coefficients, the radiation scattering spectra, and the plasma temperature with the results of experiments performed using an apparatus with an Nd3+ laser operating at the wavelengths 1.06, 0.53, and 0.35 μ in a wide range of power densities from 1013 to 3×1015 W/cm2 .

Optical recording of data on paper using CO2and YAG:Nd3+lasers

The results are given of investigations of direct laser printing methods. These are based on the effects of the interaction of high-power laser radiation with thin films of printing ink, deposited on paper and on other media. The characteristics of the printing processes were determined experimentally and their resolving power and printing rate were estimated. It was found that it should be possible to use CO2 and YAG:Nd3+ lasers for printing out data from a computer.

Conference on Laser Fusion, Leipzig, December 11–14, 1979

A brief review is given of the papers presented at the Thirteenth European Conference on Laser-Matter Interaction and Laser Fusion, held in Leipzig in 1979. An analysis is made of papers reporting research on high-power laser facilities, theoretical, numerical, and experimental investigations of laser compression and thermonuclear combustion of targets, problems relating to the physics of interaction of high-power laser radiation with high-temperature plasma, as well as the technology of laser fusion targets.

Thermal interaction of high-power laser radiation with gases

The paper is concerned with the study of thermal interaction of radiation with a quiescent medium and with a medium in co- and counter-current flow over the path being traversed by radiation. Operation of a gas lens focusing high-power lasing in the case when radiation-induced heat generation contributes additionally to temperature nonuniformity is considered. The conditions required for self-focusing of stationary Gaussian and circular beams the intensity of which decreases towards the beam center are studied. Dynamics of thermal and optical processes in the case of “banana” self-focusing is considered.

Suppression of thermal crisis in resonant interaction of high-power laser radiation with a gas stream

An analysis is made of the phenomenon of thermal crisis in a supersonic stream of a chemically reacting gas mixture. Conditions are found under which the crisis situation cannot appear. It is shown that laser radiation can be used to control gasdynamic processes in such streams and, under certain conditions, to suppress a thermal crisis.