Frequency stability of RF-excited CO2 waveguide lasers in gain-switched and Q- switched regimes

In this paper we analyze the behavior of RF-excited waveguide laser both in a gain-switched and a Q-switched regime measuring the frequency sweep during the optical pulse. This enables us to directly distinguish laser induced medium perturbations (LIMP) from the effects of the discharge power loading. Our experimental observations confirm that the main perturbation in the laser output frequency is to be attributed to thermal energy variations. This gives the result of a Q-switch chirp more than one order of magnitude smaller than in the pulsed current mode, suggesting the use of Q-switching waveguide lasers in applications such as long range or doppler laser radar systems. The chirp behavior in the pulsed current mode can show overshot relaxation corresponding to the propagation of density waves in the guide.