Abstract

Since supercontinuum generation has been traditionally identified with low-order nonlinear optical processes such as self-focusing, self-phase modulation, and four-wave mixing, the recent observation¹ of continuum generation at 0.6 μm in both inert and molecular gases has come as no small surprise: The third-order nonlinear susceptibility responsible for the leading term in the nonlinear refractive index of isotropic media is as much as 10⁶ times smaller for gases than for liquids or solids, suggesting that gases are unlikely candidates for strong nonresonant nonlinear effects. The practical significance of this discovery is that continuum generation in the UV spectral range now becomes much more feasible. Owing to the strongly increasing likelihood of optical damage in condensed media as the wavelength decreases, the availability of a gaseous medium for the generation of ultrashort continuum pulses in the UV has at least in principle significantly extended the frequency range within which time-resolved absorption spectroscopy can be effectively performed. Broad access to the UV absorption bands of simple gas phase molecules offers many new opportunities to investigate unimolecular photochemical reactions. Indeed, gas phase supercontinuum generation at 308 nm has already been reported² and further applied³ to obtain high quality transient spectra in the near UV.

© 1990 Optical Society of America