Mode study, beam characteristics of a 100 mW cw 337 μm HCN waveguide laser

The first continuous sub-millimeter waveguide laser operating on the 337 micron HCN line is described. Results of the first comprehensive experimental study of its low-loss modes are presented. The laser cavity is a 5 cm dia, 2.4 m long pyrex tube with plane reflectors (one of them is a metal mesh) against its ends. Eight modes were identified. Intensity distributions in the beam cross section and mode polarization were studied. The results agree with theoretical predictions for dielectric waveguide modes. The propagation of the EH sub 11 mode in free space was also studied. The beam propagates as a Gaussian beam at moderate, and large distances from the mesh coupler. The maximum output power of the laser is of the order of 100 mW representing the highest output power unit volume so far reported for a continuous HCN laser.