An optical-field-induced plasma amplifier for short-pulse vacuum UV radiation

Abstract

Practical short-wavelength lasers in the vacuum-UV (VUV) spectral region are in high demand in fields such as photolithography and photochemical science because of their fine spatial resolution and ease in triggering reactions. In addition, because VUV emissions do not exist in the atmosphere, they may lead to interesting new phenomena.1, 2 However, few laser media can access this spectral region. Indeed, gas lasers still dominate, especially in the deep VUV (<160nm), where they produce emissions directly. Solid-state laser media, on the other hand, must employ nonlinear wavelength conversion, with a concomitant lowering of efficiency and output. Development of gaseous lasers is further encouraged by the transparent optics at wavelengths down to 105nm. However, the availability of such lasers is limited by our lack of knowledge about their operation. Among existing gaseous lasers, discharge-pumped argon fluoride (ArF) (193nm) and fluorine (F2) (157nm) enjoy the most widespread use. We have been investigating efficient emission sources using rare-gas excimer molecules, such as Ar2* at 126nm and Kr2* (krypton) at 147nm. These deep-VUV lasers are assumed to have unique characteristics in terms of laser-material interactions. The emission wavelength is so short that the penetration depth into materials is also short, usually in the nanometer range. For most materials, the VUV emission energy should thus be absorbed in a very shallow nanorange-thin layer. We have realized nanorange surface alteration of transparent materials such as silicon dioxide (SiO2) using Ar2* excimer lamp emission at 126nm.1 High-quality silicon nitride thin films were produced by irradiating Ar2* excimer emission in silane and ammonia.2 Figure 1. Laser intensity dependence of the harmonic (integer frequency multiple) intensity (I) and ion signal. Xe: Xenon.