Nonlinear reflection of high intensity picosecond laser pulse from overdense plasma

The interaction of 1.5 ps FWHM laser pulses with solid targets at intensity 1015–1017 W/cm2 and contrast ratio 106 is studied. Red shift of a “mirror” reflected fundamental wave and its second harmonic depending on the incident laser pulse energy and angle of incidence are observed. They are associated with Doppler shift corresponding to inward movement of the critical density surface from laser pondermotive pressure. Back scattered light has nonlinear dependence from laser intensity connected with SBS and changing of plasma surface.