Introduction

Since the development of the first laser in the infrared portion of the spectrum, scientists have attempted to obtain lasing at ever shorter wavelengths. At thesame time, the development of high-powered visible and near-infrared lasers hasled to the creation of efficient nonlinear multiplication schemes to produce.usefulamounts of UV coherent light from longer-wavelength driving lasers. In the last15 years these ideas have been successfully extended into the vuv, so much sothat there now exist sources of coherent light at virtually any VUV wavelengthdown to nearly 1100 Å. This highlights many of the advances that thisfield has made in the last five years in pushing into the region shorter than 1100 Å.