High harmonic generation in a laser plasma

The results of investigation of high harmonics of radiation of a Ti:sapphire laser propagating through a laser plasma generated on the surface of different targets are presented. For most of the targets, the intensity distribution of the high harmonics generated is found to form a plateaulike pattern similar to that observed in the case of gas jets. The generation of high harmonics (up to the 65th harmonic, λ = 12.24 nm) is caused by the interaction of femtosecond laser radiation with ions. The conversion efficiency in the plateau region varies from 10−7 to 8 × 10−5 depending on the target. The main restriction on the conversion efficiency and the peak intensity of the harmonics generated is caused by the self-defocusing of the femtosecond radiation due to free charge carriers formed as a result of tunnel ionization.