Longitudinal mode selection by injection in a high pressure CO(2) laser

Single longitudinal mode (SLM) selection in a 10-atm CO(2) laser is reported. Experiments have been performed with cw injection of 1 mW/cm(2) or pulsed injection of 1 mJ/cm(2) (in 50 ns) around CO(2) line centers. A simple analytical formula of the minimum intensity required for injection of a frequency nu has been obtained. It gives the dependence vs the two most important parameters: (1) the detuning nu-nu to the center nu of the net gain curve, (2) the detuning deltanu(Kappa) to the nearest longitudinal mode of the cavity. The comparison with experimental results published on TEA lasers is very successful. The application of the formula shows the possibility of SLM selection continuously tunable in a high pressure CO(2) laser with <1 mW/cm(2) if a grating is incorporated in the cavity, and with a pulsed source of 1 kW/cm(2) without any selective element. The actual sources suitable for this purpose are reviewed.