Generation of high-order spatially coherent harmonics from solid targets by femtosecond laser pulses

Abstract

This paper discusses the generation of high-order optical harmonics from solid targets using laser pulses of 35 and 120 femtoseconds. Harmonics up to the 35th order were observed. High conversion efficiency has been achieved, e.g., ${10}^{\ensuremath{-}6}$ to the $10\mathrm{th}$ harmonic. It is demonstrated that the harmonic emission is highly directional and that the harmonic efficiency decreases rapidly with increasing plasma scale length.