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This paper presents an investigation of terahertz (THz) wave generation by optical rectification of a Gaussian laser pulse propagating in plasma having periodic density perturbation in the presence of an externally applied static magnetic field in the axial direction. The nonuniform intensity of laser pulse leads to the generation of quasi-static ponderomotive force. The electrons acquire nonlinear oscillatory velocity under the influence of the force. This velocity, on coupling with the density perturbation, induces a nonlinear current density in the radial direction. This nonlinear current density drives a wave, the frequency of which depends on the pulse duration of the laser. The frequency falls in the THz range if the pulse duration of the laser is chosen thoughtfully. For the resonant excitation of the radiation, phase matching is required, which is provided by the periodic density perturbation. Axially applied external magnetic field can be utilized as a controlling parameter to enhance the nonlinear coupling and the yield of the generated wave. The effect of the axial magnetic field on the generated THz intensity is investigated. Variations in THz radiation intensity as functions of the density ripple amplitude and background plasma density have also been studied. [ABSTRACT FROM AUTHOR]

Terahertz (THz) generation by an intense femtosecond Gaussian laser pulse (Gaussian in space and time) in rippled density plasma has been investigated in the relativistic regime. A component of ponderomotive force is exerted on electrons due to the variation in intensity in the direction transverse to the laser propagation that results in a transient current driving a radiation. If the pulsewidth of the laser is suitably chosen, the frequency of this generated radiation falls in the THz region. The necessary condition for phase matching is provided by the density ripple. The effects of transient focusing of the laser pulse on the generated THz amplitude have also been studied. Numerical simulations show a significant increase in the THz field strength with occurrences of relativistic ponderomotive self-focusing. [ABSTRACT FROM PUBLISHER]