Interaction Of Ultraintense Laser Pulse Research Articles

Fast electron transport in ultraintense laser pulse interaction with solid targets by rear-side self-radiation diagnostics.

We report on rear-side optical self-emission results from ultraintense laser pulse interactions with solid targets. A prompt emission associated with a narrow electron jet has been observed up to aluminum target thicknesses of 400 microm with a typical spreading half-angle of 17 degrees. The quantitative results on the emitted energy are consistent with models where the optical emission is due to transition radiation of electrons reaching the back surface of the target or due to a synchrotron-type radiation of electrons pulled back to the target. These models associated with transport simulation results give an indication of a temperature of a few hundred keV for the fast-electron population.

Effect of plasma inhomogeneity on ion acceleration when an ultra-intense laser pulse interacts with a foil target

Fast electrons generated via the interaction of ultra-intense laser pulses with a solid target can produce multi-MeV ions from laser-induced plasmas. These fast ions can be used for various applications ranging from the ion implantation to the stimulation of nuclear reactions. The most important point here is the efficiency of production of such fast ions. We analyse in detail, with the help of an analytical model and particle-in-cell simulations, the most efficient acceleration mechanisms including the ponderomotive force driving and acceleration by the shock wave, and compare the electrostatic ion acceleration at the front side and at the rear side of a foil target. We also determine the optimal plasma density distribution shaped by the laser pre-pulse.

Radiation damping effects on the interaction of ultraintense laser pulses with an overdense plasma.

A strong effect of radiation damping on the interaction of an ultraintense laser pulse with an overdense plasma slab is found and studied via a relativistic particle-in-cell simulation including ionization. Hot electrons generated by the irradiation of a laser pulse with a radiance of I lambda(2)>10(22) W microm(2)/cm(2) and duration of 20 fs can convert more than 35% of the laser energy to radiation. This incoherent x-ray emission lasts for only the pulse duration and can be intense. The radiation efficiency is shown to increase nonlinearly with laser intensity. Similar to cyclotron radiation, the radiation damping may restrain the maximal energy of relativistic electrons in ultraintense-laser-produced plasmas.

Interaction of ultraintense laser pulses with an underdense, preformed plasma channel

We report on experimental results regarding the propagation of ultraintense laser pulses in a preformed plasma channel. In this experiment, the long (4-mm) fully ionized plasma channel created by the amplified spontaneous emission (ASE) was measured by interferometry before and after the propagation of the short laser pulse. Forward spectra show a cascade of Raman satellites, which merge with one another when the laser power was increased up to critical power for relativistic self-focusing P/sub c/. The number of filaments measured by interferometry increases when the laser power increases. High conversion efficiency (/spl ap/10%) of second harmonic generation was observed in the interaction.

Weibel instability by ultraintense laser pulses

Particle-in-cell (PIC) simulations show that an anisotropic electron velocity distribution is demonstrated by ultraintense laser pulses in underdense plasmas. Recently, it is reported that the anisotropy has been experimentally demonstrated in laser-produced plasmas. It is also pointed out that gigagauss magnetic fields are generated by ultraintense laser pulses. We have already published that the Weibel-type electromagnetic instabilities can be theoretically excited by electrons in a velocity distribution with anisotropic temperature. If these electromagnetic waves are excited, the target may have a possibility not only to give rise to a new type of energy loss mechanism but also to influence the implosion characteristics. In this work, we present PIC simulation of the interaction of ultraintense laser pulses with plasmas. Intense self-generated magnetic fields is produced by the mechanism of Weibel instability in underdense plasmas.

Observation of a highly directional γ-ray beam from ultrashort, ultraintense laser pulse interactions with solids

Novel measurements of electromagnetic radiation above 10 MeV are presented for ultra intense laser pulse interactions with solids. A bright, highly directional source of γ rays was observed directly behind the target. The γ rays were produced by bremsstrahlung radiation from energetic electrons generated during the interaction. They were measured using the photoneutron reaction [63Cu(γ,n)62Cu] in copper. The resulting activity was measured by coincidence counting the positron annihilation γ rays which were produced from the decay of Cu62. New measurements of the bremsstrahlung radiation at 1019 W cm−2 are also presented.

Theory and simulation of the interaction of ultraintense laser pulses with electrons in vacuum

In order to investigate ponderomotive force in the relativistic regime, the interaction of ultraintense laser pulses with free electrons in vacuum is studied both theoretically and numerically. Various expressions for the electromagnetic field of the laser in the case of a Gaussian transverse profile are given, which take into account corrections to the monochromatic paraxial approximation, and the effects of finite pulse duration. A detailed demonstration of relativistic ponderomotive force (RPF) is established which makes apparent the domain of validity of this concept. Computer simulations are carried out using a three-dimensional test-particle code. They show the importance of the correct description of the fields, and confirm the domain of validity of the RPF which is $1\ensuremath{-}{v}_{z}/c\ensuremath{\gg}{1/kw}_{0}$, where ${v}_{z}$ is the component of the electron velocity parallel to the laser propagation direction, $c$ is the velocity of light, $k$ is the laser wave vector, and ${w}_{0}$ the beam waist at focus. Outside of this domain, the electron motion is more complicated, with a high sensitivity on the initial distance from the laser propagation axis and a relatively low energy gain.

Frequency mixing of high intensity laser light with stimulated Raman backscattered radiation in underdense plasmas

Sidescattered radiation from the interaction of an ultraintense laser pulse (P{gt}2thinspTW) with underdense helium plasmas (n{sub e}{approx}10{sup 19}thinspcm{sup {minus}3}) is measured and emission at 90{degree} from the axis of laser propagation is observed to be broadened significantly near the second harmonic ({Delta}{lambda}=30{endash}40thinspnm). This result is consistent with sum frequency mixing of forward propagating laser light and the broadened backscattered stimulated Raman scattered radiation that occurs within transient filamentary structures produced by the ponderomotive force of the focused laser pulse. {copyright} {ital 1998} {ital The American Physical Society}

Nonlinear electrodynamics of the interaction of ultra-intense laser pulses with a thin foil

An analytical description of the interaction of laser light with a foil, described as a thin slab of overdense plasma, is presented together with the results of multidimensional particle in cell simulations. The matching conditions at the foil result in nonlinear boundary conditions for the wave equation. The conditions for relativistic transparency are given. The interaction with the foil leads to shaping of the laser pulse. In the case of oblique incidence of a relativistically intense pulse, nonlinear coupling modifies the pulse polarization and causes emission of high harmonics and generation of an electric current. Strong focalization of the reflected pulse, in particular in three-dimensional simulations, is observed for normal and oblique incidence due to the induced distortion of the foil surface.

Nonlinear interaction of ultra-intense laser pulses with a thin foil

The nonlinear interaction of an ultraintense laser pulse with a thin foil modifies the shape, the frequency content and the polarization of the pulse. An analytical description of this interaction is presented, together with the results of 1D3V and 2D3V particle in cell simulations. The conditions for the relativistic transparency of a thin foil are given and are shown to lead to the sharpening of the laser pulse. Such a pulse shape is advantageous for Laser Plasma Wakefield Acceleration of charged particles. In addition it is shown that a thin foil makes it possible to extract the accelerated particles nonadiabatically in the case of laser particle acceleration in vacuum.

Kinetic processes in the overdense plasma under the action of ultra-intense laser pulses

The results of numerical and analytical investigation of the ultra-intense laser pulse's interaction with overdense plasma are presented. The mechanisms of the wave field energy transformation into the overdense plasma energy are discussed. The effects of radiation propagation deep into plasma as well as long-living vortex formation, plasma boundary instability, and the surface structures formation are obtained. The basic mechanisms for the absorption of incident radiation and the role played by polarization of the radiation are studied. Nonlinear theory of plasma surface instability in the field of the strong electromagnetic wave is developed.

Peculiarities of the overdense plasma dynamics under the action of ultra-intense laser pulses

Results of numerical and analytical investigations of ultra-intense laser pulse interaction with an overdense plasma are presented. The mechanisms of the wave field energy transformation into the overdense plasma energy are discussed. The effects of radiation propagation deep into the plasma as well as long living vortex formation, plasma boundary instability, are obtained. A nonlinear theory of plasma surface instability in the field of a strong electromagnetic wave is constructed.

Mechanism for the generation of 10(9) G magnetic fields in the interaction of ultraintense short laser pulse with an overdense plasma target.

The physical mechanism for the generation of very high ``dc'' magnetic fields in the interaction of ultraintense short laser pulse with an overdense plasma target originates in the spatial gradients and nonstationary character of the ponderomotive force. A set of model equations to determine the evolution of the ``dc'' fields is derived and it is shown that the ``dc'' magnetic field is of the same order of magnitude as the high frequency laser magnetic field.

Odd harmonic generation of ultra-intense laser pulses reflected from an overdense plasma

A method of generating odd harmonics from an intense laser incident upon a sharp vacuum-overdense plasma interface is presented. One- and two-dimensional simulations are used to investigate the interaction of ultra-intense laser pulses with a sharp vacuum-plasma interface. With an intensity greater than 10/sup 18/ W/cm/sup 2/, these pulses have a pressure greater than 10/sup 3/ Mbar creating large density oscillations and relativistic electron velocities at the surface. This results in efficient odd harmonic generation. The author present is a physical model for this harmonic generation mechanism, along with some scaling of the power in the third harmonic. This is compared with relativistic particle-in-cell simulations that include mobile and immobile ions, as well as a variety of upper shelf densities. A discussion on how ion profile modifications influence the harmonics is also presented. >

Absorption of ultra-intense laser pulses

We use simulations to investigate the interaction of ultra-intense laser pulses with a plasma. With an intensity greater than ${10}^{18}$ W/${\mathrm{cm}}^{2}$, these pulses have a pressure greater than ${10}^{3}$ M bar and drive the plasma relativistically. Hole boring by the light beam is a key feature of the interaction. We find substantial absorption into heated electrons with a characteristic temperature of order the pondermotive potential. Other effects include a dependence on the polarization of the incident light, strong magnetic field generation, and a period of intense instability generation in the underdense plasma.

Interaction of ultrahigh laser fields with beams and plasmas

The nonlinear interaction of ultraintense laser pulses with electron beams and plasmas is rich in a wide variety of new phenomena. Advances in laser science have made possible compact terawatt lasers capable of generating subpicosecond pulses at ultrahigh powers (≥1 TW) and intensities (≥1018 W/cm2). These ultrahigh intensities result in highly relativistic nonlinear electron dynamics. This paper briefly addresses a number of phenomena including (i) laser excitation of large-amplitude plasma waves (wake fields), (ii) relativistic optical guiding of laser pulses in plasmas, (iii) optical guiding by preformed plasma channels, (iv) laser frequency amplification by ionization fronts and plasma waves, (v) relativistic harmonic generation, (vi) stimulated backscattering from plasmas and electron beams, (vii) nonlinear Thomson scattering from plasmas and electron beams, and (viii) cooling of electron beams by intense lasers. Potential applications of these effects are also discussed.