Efficient High Power Stokes and Anti-Stokes Raman Frequency Generation via Polarization Tuning Enhancement

Abstract

A method for producing high-power broad-band coherent light via rotational Raman Stokes and anti-Stokes frequency generation in H2 is presented. A variety of potential applications include atmospheric imaging, ranging, and remote sensing. Another important potential application is producing a high-energy broad-band laser source to reduce plasma instabilities in inertial confinement fusion. The process presented here is divided into three steps. The polarization of the fields is tuned at each stage to control and optimize rotational Raman conversion. The system consists of a focused Stokes seed oscillator, collimated Stokes amplifier and a parametric mixer. A small Stokes seed is generated in a focused oscillator. A circularly polarized pump field is used here to supress parametric four-wave coupling, which insures good spatial beam quality and efficient energy conversion to first Stokes1. The circularly polarized Stokes seed is then combined with an opposite circularly polarized pump field in a collimated Raman amplifier. Again circular polarization suppresses competing parametric conversion to higher order Stokes or anti-Stokes fields. In the third stage a linearly polarized pump is combined with the amplified Stokes field, which is linearly polarized parallel to the pump and has comparable energy, in a collimated parametric mixer. Parallel linear polarization is used to maximize the parametric conversion in this final stage. Since collimated Raman cells are employed in the last two stages, this system in principle is scalable to large laser systems. This is a distinct advantage over conventional focused Raman systems 2,3, which by nature are limited in operation to small energy regimes by gas breakdown.