Generation of high-order harmonics of high-power lasers in plasmas produced under irradiation of solid target surfaces by a prepulse

Research on high-order harmonic generation in laser-produced plasmas is reviewed. We analyze the conditions for the generation of harmonics (up to the 101st order, λ = 7.9 nm) in the propagation of laser radiation through a weakly ionized plasma prepared by irradiating the surfaces of different targets with a laser prepulse. We discuss the findings of investigations into the resonance intensity enhancement of individual harmonics in a number of plasma formations, which have demonstrated a substantial increase in the conversion efficiency in the plateau region of the harmonic-order distribution (in particular, of the 13th harmonic in indium plasmas with the efficiency 10−4). We review the results of investigations of harmonic generation in nanoparticle-containing plasmas. Different techniques for increasing the intensity and order of the generated harmonics are discussed.