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We investigated powerful terahertz (THz) radiation from laser-driven gas plasma by theory and particle-in-cell (PIC) simulation. We proposed a model to describe THz radiation emission from a net current in plasma. We found that the well-known two-color scheme can be extended to the second laser at any even harmonic of the main laser. To strengthen the THz radiation, we proposed mid-infrared laser scheme, picosecond laser scheme, and asymmetric laser scheme. Recently, we proposed an approach to generate tunable, circularly-polarized, narrow-band THz radiation.

Hot electron emission is studied using 798 nm, 150 fs, p-polarized laser pulses at 1 × 1016 W cm−2, irradiating on plastic (CH), aluminium (Al), titanium (Ti) and copper (Cu) planar targets. The dependence of hot electron generation on atomic number Z is observed experimentally.

The magnetic field generation through inverse Faraday effect and its effects on the propagation of a circularly polarized light wave are studied in a self-consistent way for relativistic intensities. The following results are presented. (i) The magnetic field is produced by two sources, the circular motion of single electrons which produces plasma magnetization, and the inhomogeneity of both the electron density and light intensity which produces nonzero currents in the azimuthal direction. The magnetic field is calculated for various profiles of electron density and light intensity. (ii) For the case of a plane wave in a homogeneous plasma, the cutoff frequency is calculated as a function of light intensity, which is different from that without consideration of magnetic field generation. An ultra-intense magnetic field as large as hundreds of MG is obtainable in an overdense plasma where the wave can propagate owing to the induced transparency. (iii) The evolution equations for a laser beam of finite width are derived. Due to magnetic field generation, the critical power for self-focusing of the laser beam is reduced by a factor of (1+${\mathrm{\ensuremath{\omega}}}_{\mathit{p}}^{2}$/${\mathrm{\ensuremath{\omega}}}^{2}$${)}^{\mathrm{\ensuremath{-}}1}$; the magnetic field tends to reduce the effect of the electron cavitation resulting from the transverse ponderomotive force. \textcopyright{} 1996 The American Physical Society.

Effect of lower‐hybrid current drive on tearing mode instability is investigated in a drift kinetic formalism. In collisional regime the co‐driven current plays a stabilizing role to tearing mode but a destabilizing role to drift tearing mode. A competitive effect among the gradients of density, temperature and driven current at the rational surface may exist. In semicollisional regime, lower hybrid current drive increases the growth rate of tearing mode and reduces the growth rate of drift tearing mode.

Hard Kα x‐ray source profile and intense Terahertz radiation from femtosecond laser‐plasma interactions are studied. When a preplasma is presented, a weak halo surrounding a bright spot is observed in the x‐ray source. The x‐ray photons in the halo are mainly excited by the fast electrons that flow laterally near the target surface. Intense Terahertz radiation has been observed in the laser specular direction. The pulse energy of the radiation reaches tens of μJ/sr.

Recent experimental and theoretical studies on surface electron emission will be presented. A collimated fast electron beam was observed along the target surface irradiated by intense laser pulses up to 20TW when the laser is incident with large angles such as over 45 degree. Numerical simulations suggest that such an electron beam is formed due to the confinement of the surface quasistatic electric and magnetic fields. Meanwhile, an acceleration process similar to the inverse‐free‐electron‐laser is found to occur and is responsible for the generation of the most energetic electrons. A general formula for electron angular distributions accounting for the quasistatic electric and magnetic fields is given. In certain conditions, quasi‐monoenergetic electron beams are also produced. These results are of interest for potential applications of laser‐produced electron beams and helpful to the undersanding of the cone‐target physics in the fast ignition related experiments.

The emission direction of outward-ejecting fast electrons generated in laser-solid interactions by 30 fs laser pulses is measured for laser intensities varying from the nonrelativistic to the relativistic. For an s-polarized incident laser beam at nonrelativistic intensities, the ejected electrons are close to the polarization direction of the laser beam. With the increase of the laser intensity, the ejected electrons are still mainly within the polarization plane, but turn away from the laser polarization direction towards the opposite direction of the incident laser beam. At relativistic intensities, electrons eject towards the direction of the reflected laser beam. The increasing ponderomotive force acceleration with the laser intensities might be responsible for the observed changes.

By using three-dimensional particle-in-cell simulations with synchrotron radiation damping incorporated, dynamics of ultra-intense laser driven mass-limited foils is presented. When a circularly polarized laser pulse with a peak intensity of ∼1022 W/cm2 irradiates a mass-limited nanofoil, electrons are pushed forward collectively and a strong charge separation field forms which acts as a “light sail” and accelerates the protons. When the laser wing parts overtake the foil from the foil boundaries, electrons do a betatron-like oscillation around the center proton bunch. Under some conditions, betatron-like resonance takes place, resulting in energetic circulating electrons. Finally, bright femto-second x rays are emitted in a small cone. It is also shown that the radiation damping does not alter the foil dynamics radically at considered laser intensities. The effects of the transverse foil size and laser polarization on x-ray emission and foil dynamics are also discussed.

Magnetic field generation in the plasma wake of a relativisticly intense short pulse is studied, both analytically and by PIC-code simulation. We show that the magnetic field scales like (mωpc/e)dIL/dr⊥ in this case, different from (mωpc/e)dIL2/dr⊥ for the low intensity case. The magnetic field profiles are calculated both for β=1 and β

Kinetic beta-induced Alfven eigenmodes (KBAEs) driven by energetic ions are numerically investigated using revised AWECS code. The thermal ion density and temperature gradients are taken into account. It is found that the growth rate of the KBAEs increases with the thermal ion pressure gradient, and the contributions from the density gradient and temperature gradient of the thermal ions to the enhancement of the instability are comparable. The damping effect of thermal ion dynamics on the modes is also observed.

We studied the transport of an intense electron beam produced by high intensity laser pulses through metals and insulators. Targets were irradiated at two different intensities, 1017 W/cm2 and 1019 W/cm2, at the laser facility Xtreme Light XL-III in Beijing, a Ti:Sa laser source emitting 40 fs pulses at 800 nm. The main diagnostic was Cu - K α fluorescence imaging. Images of K α spots have been collected for those two laser intensities, for different target thickness, and for different materials. Experimental results are analyzed taking into account both collisional and collective effects as well as refluxing at the edge of the target. The target temperature is evaluated to be Tc ∼ 6 eV for intensity I 1017 W/cm2 (for all the tested materials: plastic, aluminium, and copper), and Tc ∼ 60 eV in aluminium and 120 eV in titanium for intensity I 1019 W/cm2. © 2013 American Institute of Physics.

A particle-in-cell simulation is used to investigate the ion acceleration in the interaction of an intense laser pulse with laser-induced plasma Bragg grating (PBG). For moderate laser intensities, ions are accelerated inside the PBG due to the existence of local sheath fields. For more intense laser pulse, a low frequency electromagnetic field is trapped inside the PBG, forming solitons. The soliton breaking leads to the generation of fast ions and provides a novel mechanism for laser driven ion acceleration.

Collisionless electrostatic shock (CES) waves induced by laser-plasma interactions are studied via a series of 1D and 2D particle-in-cell (PIC) simulations. Different target thicknesses, plasma densities and laser intensities have been used to investigate the shock characteristics, since all of them have significant effects on the absorption of the incident laser pulse and the electron temperature. An analytical model has been presented according to momentum conservation and considering the electrons' circulation. Thinner target, lower plasma density and higher laser intensity help to obtain higher energy ions on condition that the CES is formed.

A scheme for focusing relativistic electron beams has been proposed by use of a solid cone based upon two dimensional particle-in-cell simulations. We compare the transport of hot electrons, produced during the interaction of ultra-intense laser pulse with the targets, through the cone shape target and a flat target. It is found that relativistic electrons can be confined and focused effectively in the cone target case, where both the electron density and temperature have been increased more significantly than the flat target case.

We investigated numerically the formation and propagation of the electrostatic shocks in overdense plasmas irradiated by intense ultrashort laser pulses. The dependence of the initial shock speeds on the parameters of the plasma and the laser is explained by invoking the modified momentum conservation model. The acceleration of ions by the shocks is also discussed.

The interaction of a pump laser pulse with a counterpropagating additional laser pulse and resulting electron injection into the wakefield of the pump pulse in rarefied plasmas is analyzed. The impact of laser parameters on the injected electron number is discussed. When the injection pulse is moderately intense, the injected electron number increases with the injection pulse duration until it reaches some critical value beyond which the injected electron number is saturated. The critical pulse duration is estimated analytically and confirmed by particle-in-cell simulations. When the injection pulse intensity is decreased, the pump pulse intensity should be increased for the injection to occur. In this case, the injection pulse can only slightly affect the wakefield of the pump pulse. The injected electron number can increase with growing injection pulse duration continuously up to some limit that the wakefield can support.