Erez Raicher

Analytical Solutions of the Dirac and the Klein-Gordon Equations in Plasma Induced by High Intensity Laser

In this paper we obtain analytical solutions of the Dirac and the Klein-Gordon equations coupled to a strong electromagnetic wave in the presence of plasma environment. These are a generalization of the familiar Volkov solutions. The contribution of the non-zero photon effective mass to the scalar and fermion wavefunctions, conserved quantities and effective mass is demonstrated for the first time. The new wavefunctions exhibit differences from Volkov solutions for nowadays available laser intensity.

Relativistic shock waves induced by ultra-high laser pressure

This paper analyzes the one dimensional shock wave created in a planar target by the ponderomotive force induced by very high laser irradiance. The laser-induced relativistic shock wave parameters, such as compression, pressure, shock wave and particle flow velocities, sound velocity and temperature are calculated here for the first time in the context of relativistic hydrodynamics. For solid targets and laser irradiance of about 2× 10 24 W/cm 2 , the shock wave velocity is larger than 50% of the speed of light, the shock wave compression is larger than 4 (usually of the order of 10) and the targets have a pressure of the order of 10 15 atmospheres. The estimated temperature can be larger than 1 MeV in energy units and therefore very excited physics (like electron positron formation) is expected in the shocked area. Although the next generation of lasers might allow obtaining relativistic shock waves in the laboratory this possibility is suggested in this paper for the first time.

Equation of state for aluminum containing helium bubbles

A theoretical model for equation of state (EOS) of aluminum with helium bubbles is presented. Based on this EOS, the influence of helium bubbles on shock loading is examined. The Hugoniot curve (temperature versus pressure as well as shock velocity versus particle velocity) for aluminum containing bubbles is calculated for various bubbles mass, bubbles percentage, and helium EOS models. The bubble mass and concentration seem to affect the measurably Hugoniot curve. The EOS model, implied for the helium in the bubbles, has minor significance, which means our model is not sensitive to the details of the helium EOS. Our findings are consistent with experiments available in the literature.

The Lagrangian formulation of strong-field quantum electrodynamics in a plasma

The Lagrangian formulation of the scalar and spinor quantum electrodynamics in the presence of strong laser fields in a plasma medium is considered. We include the plasma influence in the free Lagrangian analogously to the “Furry picture” and obtain coupled equations of motion for the plasma particles and for the laser propagation. We demonstrate that the strong-field wave (i.e., the laser) satisfies a massive dispersion relation and obtain self-consistently the effective mass of the laser photons. The Lagrangian formulation derived in this paper is the basis for the cross sections calculation of quantum processes taking place in the presence of a plasma.

Mitigation of hot electrons from laser-plasma instabilities in high-Z, highly ionized plasmas

Hard x-ray measurements are used to infer production of hot electrons in laser-irradiated planar foils of materials ranging from low- to high-Z. The fraction of laser energy converted to hot electrons, fhot, was reduced by a factor of 103 going from low-Z CH to high-Z Au, and hot electron temperatures were reduced from 40 to ∼20 keV. The reduction in fhot correlates with steepening electron density gradient length-scales inferred from plasma refraction measurements. Radiation hydrodynamic simulations predicted electron density profiles in reasonable agreement with those from measurements. Both multi-beam two-plasmon decay (TPD) and multi-beam stimulated Raman scattering (SRS) were predicted to be above threshold with linear threshold parameters that decreased with increasing Z due to steepening length-scales, as well as enhanced laser absorption and increased electron plasma wave collisional and Landau damping. The results add to the evidence that SRS may play a comparable or a greater role relative to TP...

Nonlinear Compton scattering in a strong rotating electric field

The non-linear Compton scattering rate in a rotating electric field is explicitly calculated for the first time. For this purpose, a novel solution to the Klein-Gordon equation in the presence of a rotating electric field is applied. An analytical expression for the emission rate is obtained, as well as a simplified approximation adequate for emplementation in kinetic codes. The spectrum is numerically calculated for nowadays optical and X-ray laser parameters. The results are compared to the standard Volkov-Ritus rate for a particle in a plane wave, which is commonly assumed to be valid for a rotating electric field under certain conditions. Subsequent deviations between the two models, both in the radiated power and the spectral shape, are demonstrated. First, the typical number of photons participating in the scattering process is much smaller compared to the Volkov-Ritus rate, resulting in up to an order of magnitude lower emitted power. Furthermore, our model predicts a discrete harmonics spectrum for electrons with low asymptotic momentum compared to the field amplitude. This discrete structure is a clear imprint of the electric field frequency, as opposed to the Volkov-Ritus rate which reduces to the constant crossed field rate for the physical conditions under consideration. Our model predictions can be tested with present-days laser facilities.

A novel solution to the Klein–Gordon equation in the presence of a strong rotating electric field

Abstract The Klein–Gordon equation in the presence of a strong electric field, taking the form of the Mathieu equation, is studied. A novel analytical solution is derived for particles whose asymptotic energy is much lower or much higher than the electromagnetic field amplitude. The condition for which the new solution recovers the familiar Volkov wavefunction naturally follows. When not satisfied, significant deviation from the Volkov wavefunction is demonstrated. The new condition is shown to differ by orders of magnitudes from the commonly used one. As this equation describes (neglecting spin effects) the emission processes and the particle motion in Quantum Electrodynamics (QED) cascades, our results suggest that the standard theoretical approach towards this phenomenon should be revised.

Soft X-ray emission from laser-irradiated gold foils

This paper reports measurements of soft-x-ray emission from gold foils irradiated by 6 ns laser pulses, and analysis and simulations of the observations. These foils can be used as x-ray sources to drive a wide range of experiments. A multichannel, photodiode array measured the time-resolved, soft-x-ray emission. A soft-x-ray framing camera imaged the emission in selected energy bands. Foil thicknesses were from 0.5 to 1.5 μm. The imaging data show that the region emitting soft x-rays grows throughout the laser drive, on both the front and rear surfaces. Analysis of the emitted radiation flux from the rear surface, taking the time-dependent spot size into account, showed that the peak effective temperature of 0.5-μm-thick foils is near 88 eV, while that of 0.75-μm-thick foils is near 78 eV. A Monte Carlo method was used to evaluate the component of the uncertainty in the effective temperature introduced by variations in signal voltages and by uncertainty in the size of the emitting spot. This was found to...

The non-linear Compton scattering in plasma obtained using a novel analytical solution of the strong-field Klein-Gordon

The matrix element of the Compton scattering in the presence of strong electromagnetic field in plasma is considered. The calculation is performed employing two novel wavefunctions, numerical and analytical, describing the dynamics of the particle in the electromagnetic field. The impact of the analytical approximation on the matrix element of the scattering process is investigated.

Influence of atomic modeling on integrated simulations of laser-produced Au plasmas.

Time-integrated x-ray emission spectra of laser-irradiated Au disks were recorded using transmission grating spectrometry, at laser intensities of 10(13) to 10(14) W/cm(2). Radiation-hydrodynamics and atomic physics calculations were used to simulate the emitted spectra. Three major plasma regions can be recognized: the heat wave, the corona, and an intermediate region connecting them. An analysis of the spectral contribution of these three plasma regions to the integrated recorded spectrum is presented. The importance of accurate atomic modeling of the intermediate plasma region, between the corona and the heat wave, is highlighted. The influence of several aspects of the atomic modeling is demonstrated, in particular multiply-excited atomic configurations and departure from local thermal equilibrium.