Abstract

High-order optical harmonics generation (HHG) has recently attracted much attention as a possible source of short-wavelength coherent radiation [1]; harmonics of the order up to the 135th and wavelengths as short as 7.6 nm have been observed [2,3]. Conversion efficiency of HHG, however, remains too low for applications, largely due to poor phase matching. Phase­matching optimization could substantially increase the output. The actual experimental conditions, however, are, most likely, very far from optimal. Indeed, reported HHG experiments are conducted in almost dispersionless (gases) or positively dispersive (plasma) media, whereas phase-matching optimization of HHG, at least according to perturbation theory, requires strong negative dispersion, if beam are focused. To avoid this obstacle, another multiphoton process, high-order difference frequency mixing (HDM)

© 1994 Optical Society of America