Abstract

We describe experimental observations of high-order harmonic generation in rare gases. The incident radiation field is a 1064-nm 30-ps Nd:YAG laser. A gas jet provides a 1-mm wide nonlinear medium at 15-Torr pressure. The highest harmonics detected in Xe, Kr, and Ar are, respectively, the twenty-first, twenty-ninth, and thirty-third at approximately the same laser intensity of ~3 × 10¹³ W · cm⁻². The harmonics distribution decreases steeply from the third to fifth harmonic, then presents a nearly flat plateau with, however, some anomalies in Ar and Kr in the vicinity of discrete excited states. We examine the phase matching conditions for generation of the different harmonics: our aim is to disentangle what is due to the macroscopic properties of the medium, i.e., pressure, geometry, influencing the phase matching, and, therefore, the conversion efficiency to what is characteristic of the individual atom in an intense field, i.e., nonlinear atomic susceptibilities and polarizabilities.

© 1988 Optical Society of America