Output Power Optimization and Gain and Saturation Irradiance Measurements on a RF-Pumped HCN Waveguide Laser

A 1-m-long RF-pumped HCN waveguide laser is described. Output power optimizations were performed with mixtures of methane, nitrogen, and helium in the ratios 1:2:0, 1:1:0, 2:1:0, and 8:3:36. The variation of output power as a function of gas pressure, flow rate, waveguide wall temperature, and RF driving power was studied. A maximum output power of approximately 50 mW was obtained from the 337-mum line in the EH(11) cavity mode with the 1:1:0 mixture. Gain and saturation irradiance measurements were also performed on the same laser with an adjustable Michelson output coupler. The output power was measured as a function of the adjustment of the coupler, and a least-squares fit of a suitable laser model to the measured data was employed to furnish values for the small signal gain and saturation irradiance of the gain medium. Gain and saturation irradiance values were measured in this way for the above gas mixtures as a function of gas pressure, flow rate, and wall temperature, and the results were used to calculate the corresponding output powers. Reasonable agreement was found between these calculated powers and experimentally measured output powers. A quadratic variation of saturation irradiance with pressure is predicted by a simple theory and is also observed in the measured data.