Power broadening and the basic limitations of CW optically pumped far-infrared laser performance

Power broadening is shown to be important for the line profile of the pump absorption coefficient of optically pumped far-infrared laser gases. Calculations of the pump absorption have to account for power broadening in order to correctly represent the flow of energy during the laser cycle. An analytic expression is derived for the power broadened absorption in the case of resonantly pumping the center of the absorption line. The basic limitations of far-infrared laser performance are the maximum pump power per volume that a molecular gas can absorb as well as the maximum far-infrared power per volume that the gas is able to produce. Closed expressions evolving from the power broadening considerations are given for both quantities. It turns out that both are basically determined by only two physical properties of the laser gas, namely the energy of the lower pump level and the rotational relaxation rate