The growth of laser oscillations at high excitation

The buildup of single-mode laser oscillations is investigated for the 0.633-μ transition of a helium-neon laser at levels of relative excitation significantly above threshold (
1.5 \leq n \leq 4
) using a fast intra-cavity chopper. The time response agrees with theory. The evolution of the signal provides information on the saturation mechanism and allows a very simple determination of resonator quality, relative excitation, unsaturated gain, and degree of saturation of a laser. The saturation parameter is found to depend on the discharge current. This is attributed to a variation of the gas density in the capillary discharge tube caused by gas heating, which affects the collision-dominated atomic lifetimes.