A high energy electron density modulator from a high-intensity laser standing wave field is studied herein by investigating the ultrafast motion of electrons in the field. Electrons converge at the electric field antinodes, and the discrete electron density peaks modulated by the field located at the corresponding laser phases of kx = nπ, (n = 0, 1, 2, …), that is, the modulation period is 1/2 the wavelength of the individual laser. We also discussed the influence of the laser parameters such as laser intensity and waist size on the beam modulator. It is shown that a long interaction length (waist) or sufficiently high field intensity is essential for relativistic electron density modulation.

Laser beat wave heating of magnetized plasma via electron cyclotron damping is proposed and analyzed. A plasma density ripple is presumed to exist across the magnetic field. Two collinear lasers propagating along the magnetic field exert a beat frequency ponderomotive force on electrons, driving a large amplitude Bernstein quasi-mode which suffers cyclotron damping on electrons. Finite Larmor radius effects play an important role in the heating. Electron temperature initially rises linearly with time. As the temperature rises cyclotron damping becomes stronger and temperature rises rapidly. The process, however, requires ripple wavelength shorter than the wavelength of the beat wave.

The possibilities of electron acceleration by ponderomotive force of a circularly polarized laser pulse in magnetized quantum plasma have been explored. The basic mechanism involves acceleration of electron by the axial gradient in the ponderomotive potential of the laser. The quantum effects have been taken into account for a high-density plasma. The ponderomotive force of the laser is resonantly enhanced when Doppler up-shifted laser frequency equals the cyclotron frequency.

Ponderomotive non-linearities arising by propagation of a linearly polarized laser beam through high-density quantum plasma are studied. The intense laser beam sets the plasma electrons in quiver motion and consequently ponderomotive non-linearity sets in leading to electron density perturbation inside the plasma. The interaction formalism has been built using the quantum hydrodynamic model. Laser beam traversing through high-density quantum plasma acquires an additional focusing tendency due to the perturbation induced by ponderomotive force in the plasma density. The ponderomotive force causes the beam to focus and the quantum effects contribute in focusing. The transverse magnetization of quantum plasma enhances the self-focusing and increase in magnetic field limits the spot size.

In the interaction of ultra-short and ultra-intense high contrast laser pulse with a dense foil, accelerating electron sheath is formed. The dynamic of this sheath is obtained according to the ponderomotive force of the laser pulse and restoring electrostatic force of the stationary heavy ions. In the transient dynamics, maximum electron sheath displacement is obtained for different interaction parameters. This maximum displacement has an important effect in the explanation of the electron blow out condition. It is shown numerically that the electron sheath maximum displacement increases with increasing laser pulse amplitude or decreasing its rise time, or by decreasing plasma electron density. Recently, backward MeV acceleration of electrons in the interaction of intense laser pulse with solid targets was observed. The ponderomotive force of the compressed reflected laser pulse includes in our formalism and is used for explanation of the electron's backward acceleration. The threshold values of the interaction parameters for the occurrence of this phenomenon are considered. The electron blow out condition and backward acceleration are accompanied with numerical modeling and 1D3V, particle-in-cell simulation code.

Stimulated Raman backward scattering of an X-mode laser beam propagating in a homogenous plasma is studied in the presence of a transverse magnetic field. As the laser propagates in its X-mode in plasma, it decays into an upper hybrid wave and a down-shifted sideband wave. Beating the incident laser with the sideband exerts a nonlinear ponderomotive force acting on plasma electrons driving the excited upper hybrid wave. The incident wave then parametrically couples with the upper hybrid wave to drive the sideband. Using the fluid model and nonlinear current density, the nonlinear ponderomotive force is obtained to find the dispersion relation of the scattered sideband wave and the growth rate of the instability in the weakly relativistic regime. It is shown that the growth rate decreases and the cut-off points in the normalized wave number of the upper-hybrid wave become smaller by increasing the static magnetic field.

The nonlinear propagation of high power microwave beam in unmagnetized collisional plasma is studied taking into account the ponderomotive force, space charge and Ohmic heating effects. It is shown that the amplitude of electron temperature distribution is enhanced by increasing the microwave energy flux, and decreases when the microwave frequency increases. It is also demonstrated that the steepening of the electron density distribution increases when the amplitude of electron temperature profiles reduces and vice versa. Furthermore, by increasing the initial electron density, the amplitude and number of peaks are decreased, but the electron density distribution, the space charge field and the dielectric permittivity profiles are increased.

Brillouin backward scattering is investigated in the interaction of linearly polarized short laser pulse with a homogenous underdense transversely magnetized plasma by taking into account the relativistic and nonlinearity effects up to third order. The plasma is embedded in a uniform magnetic field perpendicular to both of propagation direction and electric vector of the radiation field. Temporal growth rate of instability is calculated by using of the nonlinear wave equation. Results are significantly different in comparison with lower order computations. The growth rate of Brillouin backward instability shows a decrease due to the presence of external magnetic field, while relativistic and higher order nonlinearities due to the external magnetic field, give rise the Brillouin backward scattering instability.

Hemispherical electron plasma waves generated from ultraintense laser interacting with a solid target having a subcritical preplasma is studied using particle-in-cell simulation. As the laser pulse propagates inside the preplasma, it becomes self-focused due to the response of the plasma electrons to the ponderomotive force. The electrons are mainly heated via betatron resonance absorption and their thermal energy can become higher than the ponderomotive energy. The hot electrons easily penetrate through the thin solid target and appear behind it as periodic hemispherical shell-like layers separated by the laser wavelength.

The third harmonic generation of a self organized nonlinear laser Eigen mode of a two-dimensional plasma channel with complete electron evacuation from the inner region is investigated. The nonlinearities arise through the ponderomotive force and relativistic mass variations, while the ions are taken to be immobile. The second harmonic ponderomotive force produces electron density oscillations that beat with the oscillatory velocity due to the laser Eigen mode to create a nonlinear current, driving the third harmonic. As a0 increases up to the threshold value amin, at which complete electron evacuation begins in the inner region, the third harmonic amplitude rises rapidly. Above the threshold, as a0 increases, the width of the inner region where there is no third harmonic current, increases and third harmonic amplitude rises less rapidly. The conversion efficiency is found to be in reasonable agreement with the experimental results.

In this work, it is suggested that the ponderomotive force, induced by a multi-petawatt laser on the interface of a vacuum with solid target, can accelerate a micro-foil to relativistic velocities. The extremely high velocities of the micro-foil can be achieved due to the very short time duration (about a picosecond) of the laser pulse. This accelerated micro-foil is used to ignite a pre-compressed cylindrical shell containing the deuterium tritium fuel. The fast ignition is induced by a heat wave produced during the collision of the accelerated foil with the pre-compressed target. This approach has the advantage of separating geometrically the nanoseconds lasers that compress the target with the picosecond laser that accelerates the foil.

Raman backward scattering is investigated in the interaction of linearly polarized ultra short laser pulse with a homogenous cold underdense magnetized plasma by taking into account the relativistic effect and the effect of nonlinearity up to third order. The plasma is embedded in a uniform magnetic field perpendicular to both of propagation direction and electric vector of the radiation field. Nonlinear wave equation is set up and differential equations, which model the instability, are derived. Using of the Fourier transformation, analytical solutions are obtained for a set of physically relevant initial conditions and the temporal growth rate of instability is calculated. Results are significantly different in comparison with lower order computations. The growth rate of backward Raman scattering shows an increase due to the presence of external magnetic field as well as nonlinear effects.

The results of numerical and experimental studies of high-intensity proton beam generation using a 2ω or 1ω Nd:glass laser beam irradiating a thin hydrogen-rich target are reported. The effect of the laser wavelength (λ), intensity (IL) and pulse duration as well as the target thickness, and the preplasma density gradient scale length on proton beam parameters, and the laser-protons energy conversion efficiency were examined by particle-in-cell simulations. Both the simulations and measurements, performed on the LULI 100 TW laser facility at IL up to 2 × 1019W/cm2, prove that at the ILλ2 product fixed, the 2ω laser driver can produce proton beams of intensity, current density and energy fluence significantly higher than the ones which could be achieved using the 1ω driver. In particular, at ILλ2~(0.5–1) × 1020 Wcm−2 µm2 the 2ω picosecond driver makes it possible to generate multi-MeV proton beams of intensity and current density in excess of 1021W/cm2 and 1014A/cm2, respectively, with the conversion efficiency above 10%.

The presence of an axial magnetic field in a laser beat wave accelerator enhances the oscillatory velocity of electrons due to cyclotron resonance effect leading to higher amplitude of the ponderomotive force driven plasma wave, and higher energy of accelerating electrons. The axial magnetic field inhibits the transverse escape of electrons and thus causes a growth of the interaction length. The surfatron acceleration of electrons also shows a similar enhancement. A surfatron transverse magnetic field deflects the electrons parallel to the phase fronts of the accelerating wave keeping them in phase with it. However, the electron continues to move away radially.

The interaction of electromagnetic radiation with plasmas is studied in relativistic four-vector formalism. A gauge and Lorentz invariant ponderomotive four-force is derived from the time dependent nonlinear three-force of Hora (1985). This four-force, due to its Lorentz invariance, contains new magnetic field terms. A new gauge and Lorentz invariant model of the response of plasma to electromagnetic radiation is then devised. An expression for the dispersion relation is obtained from this model. It is then proved that the magnetic permeability of plasma is unity for a general reference frame. This is an important result since it has been previously assumed in many plasma models.

A new kind of high power tunable microwave radiation source is studied theoretically and experimentally. Following the previous works presented by Dorranian et al. (2003, 2004) in this paper more details about the radiation is presented. The theory of the radiation is developed to calculate the radiation spatial distribution, and more discussion on radiation behavior and characteristics is done. In this radiation scheme, a part of large amplitude electrostatic plasma wake, generated by an intense laser pulse or a relativistic electron bunch, are converted to electromagnetic oscillations by applying a modest dc magnetic field perpendicular to the wake propagation direction. A direct one-dimensional (1D) analytic procedure for calculating the magnetized plasma wake equations is developed and the properties of the radiation are investigated theoretically. The effects of the ramp plasma-vacuum boundary in coupling the radiation from plasma to vacuum is noticed and solved by employing a gas jet flow to generate a sharp boundary. Wakefield is excited by TW-100 fs Ti:sapphire laser beam operating at 800 nm wavelength. The neutral density of gas jet flow is measured with a Mach-Zehnder interferometer. The frequency of the emitted radiation with the pulse width of 200 ps (detection limitation) is in the millimeter wave range. Radiation is polarized perpendicularly to the dc magnetic field lines and propagates in the forward direction and normal direction with respect to the laser pulse propagation direction, both perpendiculars to the direction of the applied magnetic field. Intensity of the radiation in different plasma densities and different magnetic field strengths has been observed.