On absorption of the laser radiation in a plasma with subcritical density

Absorption, reflection and scattering of laser radiation have been studied in experiments with oblique incidence of Nd glass laser beams on plane massive targets of polyethylene, aluminium and copper. Time behaviour of 2ω and 3/2ω harmonic intensities and their angular distributions were measured along with plasma X-ray spectra in the flux density range 1013 to 3 x 1014 W/cm2 for 3.5 nsec laser pulses. Comparison of the experimental data with the results of the theoretical analysis and numerical calculations is presented. The hard X-ray component in the X-ray spectrum disappears at large angles of incidence, hence the supra-thermal electron generation and two-plasmon instability are proven to be coupled phenomena. (author)