Attosecond x-ray pulse generation by linear Thomson scattering of intense laser beam with relativistic electron

Linear Thomson scattering of a short pulse laser by relativistic electron lids been investigated using computer simulations. It is shown that scattering of an intense laser pulse of similar to 33 fs full width at half maximum, with an electron of gamma(o) = 10 initial energy, generates an ultrashort, pulsed radiation of 76 attoseconds, with a photon wavelength of 2.5 nm in the backward direction. The scattered radiation generated by a highly relativistic electron has superior quality in terms of its pulse width and angular distribution in comparison to the one generated by lower relativistic energy electron.

Short-pulse laser absorption in very steep plasma density gradients

An analytical fluid model for resonance absorption during the oblique incidence by femtosecond laser pulses on a small-scale-length density plasma [k(0)L is an element of(0.1,10)] is proposed. The physics of resonance absorption is analyzed more clearly as we separate the electric field into an electromagnetic part and an electrostatic part. It is found that the characteristics of the physical quantities (fractional absorption, optimum angle, etc.) in a small-scale-length plasma are quite different from the predictions of classical theory. Absorption processes are generally dependent on the density scale length. For shorter scale length or higher laser intensity, vacuum heating tends to be dominant. It is shown that the electrons being pulled out and then returned to the plasma at the interface layer by the wave field can lead to a phenomenon like wave breaking. This can lead to heating of the plasma at the expanse of the wave energy. It is found that the optimum angle is independent of the laser intensity while the absorption rate increases with the laser intensity, and the absorption rate can reach as high as 25%. (c) 2006 American Institute of Physics.

Study on the interaction of intense femtosecond laser pulses with nanometre-sized hydrogen clusters

The interaction of intense femtosecond laser pulses with hydrogen clusters has been experimentally studied. The hydrogen clusters were produced from expansion of high-pressure hydrogen gas (backed up to 8x10(6)Pa) into vacuum through a conical nozzle cryogenically cooled by liquid nitrogen. The average size of hydrogen clusters was estimated by Rayleigh scattering measurement and the maximum proton energy of up to 4.2keV has been obtained from the Coulomb explosion of hydrogen clusters under 2 x 10(16)W/cm(2) laser irradiation. Dependence of the maximum proton energy on cluster size and laser intensity was investigated, indicating the correlation between the laser intensity and the cluster size. The maximum proton energy is found to be directly proportional to the laser intensity, which is consistent with the theoretical prediction.

Transverse evolution of a plasma channel in air induced by a femtosecond laser

We investigate the evolution of filamentation in air by using a longitudinal diffraction method and a plasma fluorescence imaging technique. The diameter of a single filament in which the intensity is clamped increases as the energy of the pump light pulse increases, until multiple filaments appear. (c) 2006 Optical Society of America.

Intense laser beam guiding in self-induced electron cavitation channel in underdense plasmas

In underdense plasmas, the transverse ponderomotive force of an intense laser beam with Gaussian transverse profile expels electrons radially, and it can lead to an electron cavitation. An improved cavitation model with charge conservation constraint is applied to the determination of the width of the electron cavity. The envelope equation for laser spot size derived by using source-dependent expansion method is extended to including the electron cavity. The condition for self-guiding is given and illuminated by an effective potential for the laser spot size. The effects of the laser power, plasma density and energy dissipation on the self-guiding condition are discussed.

Standing electron plasma wave mechanism of void array formation inside glass by femtosecond laser irradiation

We investigate the mechanism of formation of periodic void arrays inside fused silica and BK7 glass irradiated by a tightly focused femtosecond (fs) laser beam. Our results show that the period of each void array is not uniform along the laser propagation direction, and the average period of the void array decreases with increasing pulse number and pulse energy. We propose a mechanism in which a standing electron plasma wave created by the interference of a fs-laser-driven electron wave and its reflected wave is responsible for the formation of the periodic void arrays.

Electron acceleration by a propagating laser pulse in vacuum

Electrons accelerated by a propagating laser pulse of linear or circular polarization in vacuum have been investigated by one-dimensional particle-in-cell simulations and analytical modeling. A stopping target is used to stop the laser pulse and extract the energetic electrons from the laser field. The effect of the reflected light is taken into account. The maximum electron energy depends on the laser intensity and initial electron energy. There is an optimal acceleration length for electrons to gain maximum energy where electrons meet the peak of the laser pulse. The optimal acceleration length depends strongly on the laser pulse duration and amplitude. (C) 2007 American Institute of Physics.

Generation of strong quasistatic magnetic fields in interactions of ultraintense and short laser pulses with overdense plasma targets

An analytical fluid model is proposed for the generation of strong quasistatic magnetic fields during normal incidence of a short ultraintense Gaussian laser pulse with a finite spot size on an overdense plasma. The steepening of the electron density profile in the originally homogeneous overdense plasma and the formation of electron cavitation as the electrons are pushed inward by the laser are included self-consistently. It is shown that the appearance of the cavitation plays an important role in the generation of quasistatic magnetic fields: the strong plasma inhomogeneities caused by the formation of the electron cavitation lead to the generation of a strong axial quasistatic magnetic field B-z. In the overdense regime, the generated quasistatic magnetic field increases with increasing laser intensity, while it decreases with increasing plasma density. It is also found that, in a moderately overdense plasma, highly intense laser pulses can generate magnetic fields similar to 100 MG and greater due to the transverse linear mode conversion process.

Electronic and kinetic processes in the Cu/CuCl double pulse laser

Kinetic and electronic processes in a Cu/CuCl double pulsed laser were investigated by measuring discharge and laser pulse characteristics, and by computer modeling. There are two time scales inherent to the operation of the Cu/CuCl laser. The first is during the interpulse afterglow (tens to hundreds of microseconds). The second is during the pumping pulse (tens of nanoseconds). It was found that the character of the pumping pulse is largely determined by the initial conditions provided by the interpulse afterglow. By tailoring the dissociation pulse to be long and low energy, and by conditioning the afterglow, one may select the desired initial conditions and thereby significantly improve laser performance. With a low energy dissociation pulse, the fraction of metastable copper obtained from a CuCl dissociation is low. By maintaining the afterglow, contributions to the metastable state from ion recombinations are prevented, and the plasma impedance remains low thereby increasing the rate of current rise during the pumping pulse. Computer models for the dissociation pulse, afterglow, pumping pulse and laser pulse reproduced experimentally observed behavior of laser pulse energy and power as a function of time delay, pumping pulse characteristics, and buffer gas pressure. The sensitivity of laser pulse properties on collisional processes (e.g., CuCl reassociation rates) was investigated.