Abstract

Stimulated Raman shifting in gases is widely used for generation of coherent radiation at new frequencies. The method is of great importance in the UV range where the frequency doubling, tripling or mixing in the nonlinear crystals fails because of the absorption and because the complexity and low efficiency of the heat pipes with metal vapours is prohibitive. Many authors have reported efficient Raman conversion of nanosecond pulses from excimer lasers [1] as well as of picosecond pulses at various wavelengths [2]. However, the long relaxation time in the gaseous Raman medium (several tens to hundreds picoseconds) has been always considered as an obstacle for efficient conversion of femtosecond light pulses, due to the highly transient nature of the stimulated Raman process [3]. The appearance of other competitive nonlinear processes such as self-phase modulation, multi-photon absorption and ionization which may gain over the stimulated Raman scattering has also been thought as a limitation of the method.

© 1992 The Author(s)