A bidirectionally emitting ring laser ${(}^{15}$${\mathrm{NH}}_3$ at 376-μm wavelength) exhibits self-pulsing and chaos. The routes to chaos are found to be either a one-frequency–period-doubling route to chaos, or a one-frequency–two-frequencies–phase-locking– period-doubling route to chaos: windows within the chaotic range, the same as reported for a two-roll Bénard convection cell experiment. In single-mode operation an instability is observed under conditions compatible with the Lorenz model.

• Received 11 March 1985

DOI:https://doi.org/10.1103/PhysRevA.31.4049