Increase in the Yield of X-rays and Terahertz Radiation from a Thin Foil Irradiated by Femtosecond Laser Pulses

It is shown experimentally that the intensities of characteristic X-rays, terahertz radiation, and the second optical harmonic from a copper foil irradiated by sub-relativistic femtosecond laser pulses increase simultaneously with decreasing foil thickness. The efficiency of the generation of X-rays and terahertz radiation, as well as the 3/2 harmonic with a various degree of nonlinearity, depends on the intensity of radiation and the duration of a laser pulse. the behavior of measured signals is determined by the instability of the two-plasmon decay, by hot electrons, and by their circulation in observed processes.