Time-dependent oscillations in a cw chemical laser unstable resonator

Measurements of the frequency and amplitude of time-dependent oscillations occurring in a CW laser employing a confocal unstable resonator are reported. The time-dependent oscillations have a period of about 40 nsec and increse in amplitude as the fraction of the resonator filled by the saturated gain of the oscillating line decreases. The period of the oscillation is independent of flow rates, and the amplitude of the oscillation depends only on the fraction of the resonator filled by the oscillating line, in agreement with the MNORO3UR computer model. As predicted by the MNORO3UR calculations, the oscillation on the lines whose saturated gain does not fill the unstable resonator do not occur for Fresnel numbers less than a demarcation value which lies between 1.5 and 3.0.