ANISOTROPIC UNIDIRECTIONAL OPERATION OF AN OPTICALLY-PUMPED CH3OH RING LASER

We report directional anisotropy of the outputs of an optically pumped far-infrared ring laser, which operates on the 119 mu m line of CH3OH , with special emphasis on the effect of the Raman-type two-photon pro cess on the unidirectional operation. By use of a Doppler broadened th ree-level system which allows the coexistence of two counterpropagatin g far infrared (fir) fields as well as a pump field in the cavity, an expression for the fir intensity determining equations is derived, A n umerical calculation has been carried out to map the threshold contour s on the parameter plane spanned by the cavity and pump detuning frequ encies. The output directionality is shown to be a direct consequence of the gain anisotropy due to the two-photon process. Furthermore, it is also noted how the dynamic Stark effect modifies the threshold cont ours of the forward output.