Abstract

Dual-wavelength pumped Raman-resonant four-wave mixing, proposed recently by us,¹ can be expected to be a very efficient method for anti-Stokes conversion of vacuum-ultraviolet (VUV) lasers or other low-power lasers. It is essentially an enhancement of Raman polarization by applying both an intense secondary pump and its Stokes fields either simultaneously with or slightly preceding the main pump pulse. A nearly 60% first-anti-Stokes conversion efficiency relative to the main pump power is theoretically predicted in the transient regime when a proper phase-matching condition (shown in the top part of Fig. 1) is satisfied. A remarkable feature of this method is that the optimum conversion efficiency is independent of the initial main pump intensity as long as a strong enough secondary pump is applied. For example, we can choose a commercial highpower laser, such as a KrF excimer laser or a Nd:YAG laser as a secondary pump source for converting a relatively weak coherent source in the VUV region, such as a F₂ laser. Moreover, with this method the interaction length required for the optimum conversion can be made much shorter than that required in an ordinary single-pump Raman conversion method. This is a significant advantage in avoiding the effects of beam walk-offs and finite coherent lengths in practical experiments.

© 1993 Optical Society of America