Generation of terahertz radiation in the interaction of a femtosecond pulse with a metal film

The action of an s-polarised femtosecond laser pulse is found to result in nonlinear currents in a metal film, which arise due to the nonuniform heating of the conduction electrons and under the influence of the drag force. The Fourier transforms of a low-frequency magnetic field generated by nonlinear currents are calculated. It is shown that when the film thickness is less than the scale of the low-frequency field nonuniformity, the amplitude of the terahertz signal increases in inverse proportion to the film thickness. If the thickness of the film is less than the depth of the skin layer at the laser frequency, the low-frequency signal is amplified inversely proportional to the square of the film thickness.