Thermal pump saturation in CW optically pumped far infrared lasers

Abstract

Vibrational-translationally relaxing far infrared (FIR) laser gases are heated by relaxation from the first vibrational state containing the lasing levels to the ground state. This reduces the molecule density, thus leading to a lower effective pump absorption compared with a cold gas. This phenomenon is investigated theoretically by solving the appropriate heat diffusion equation, considering both the traditional circular symmetric waveguide structure and the sandwich (or parallel slab) structure. The most important results are discussed and compared with previously reported experiments. A method is given for an estimation of the effective pump absorption and the excess temperature.