Observation of instabilities and chaos in a homogeneously broadened single mode and multimode midinfrared Raman laser

Observation of instabilities leading to chaos are reported in the emission from a single mode homogeneously broadened laser. For this system, a short laser cavity containing NH
3
near-resonantly pumped by pulsed CO
2
laser radiation and operating at 12 μm, we find that these effects are obtained at a considerably reduced threshold to that predicted for two-level systems and are maintained under steady-state conditions corresponding to long pulse excitation [pulse duration ∼1300 times the cavity roundtrip time (t
R
)]. Observation of such effects over a wide range of conditions for the two emissions studied here suggests that this behavior is general for this class of lasers. Dependent on operating conditions, routes to chaos are characterized by period doubling for the single mode system and intermittency, together with evidence of a Ruelle-Takens mechanism for the multimode systems.