ИСТИНА

Laser pulse propagating in an underdense plasma produces a wakefield which can be used for acceleration of trapped electrons. Also, during the wakefield formation, strong nonlinear currents are generated in plasma. Emission of intense electromagnetic radiation by these nonlinear currents is studied by 2D particle-in- cell simulation. It is shown that, depending on parameters of the laser pulse and plasma, waves of different frequencies can be generated and they propagate with different angles with respect to the laser axis. In simulations, relatively long pulses (containing many periods) of radiation with single, double and triple plasma frequency were observed so the terahertz and infrared bands can be covered by this source. The influence of a plasma density modulation on the process of emission of plasma frequency harmonics is also investigated. In this case, the amplitude of the generated radiation can be considerably increased. Characteristics of radiation generated during laser wakefield propagation in plasma such as polarization, frequency, amplitude, etc. are studied and spectral densities for different harmonics of the plasma frequency are found. It is shown that the amplitude of the radiation can be about 20 GV/m and efficiency of generation can achieve a percent. Also, an analytical model is considered for generation of terahertz or infrared radiation produced with a wakefield formed by a high-intensity laser pulse in a gas medium.