Three-mode stimulated emission from a gas laser

An experimental investigation was made of the stimulated emission of three longitudinal λ=0.6328 μ modes from an He–Ne laser. The ranges of stability of the various three-mode-locked regimes were determined as a function of the gas pressure and pumping rate. Wen the detuning of the emission frequencies relative to the center of the gain profile was varied, narrow regions of unlocking of the mode beats were observed within the locking ranges with the φ = π phase. The minimum width of such regions was less than 6 MHz. Nonlinear self-modulation with a frequency of secondary mode beats in the range 2–10 kHz was observed in these unlocking regions. The experimental results and the theory were compared by a numerical calculation of the ranges of existence and stability of symmetric and asymmetric three-mode emission.