Establishment of two-mode lasing in gas lasers

Equations describing changes in the slowly varying amplitudes and phases of the field, taking into account the slow response (inertia) of the active medium, are derived for a two-mode gas laser. It is found that allowance for the inertia does not influence steady-state lasing, but the conditions for the attainment of a steady-state value depend strongly on the degree of inertia of the medium and the intermode interaction. Theoretical and experimental studies were made of the influence of the scanning rate of the resonator modes on the lasing regime. It was found that when the medium had a long response time, the characteristics of the two-mode regime depended strongly on the scanning rate. A comparison was made between the lasing characteristics when single-mode and two-mode regimes were established. Numerical calculations and experimental investigations were made for a CO₂ laser.