Abstract

Bidirectional ring lasers when detuned can exhibit spontaneous intensity pulsations ranging in form from alternating square waves to periodic and chaotic waveforms. Numerical studies of a model with adiabiatic elimination of the polarization show that the optical frequencies of the two modes are not constant but change during the pulsations. Square wave pulsations cause dramatic frequency shifts as the signal changes from growing to nearly constant (at the steady state value) to decaying. More irregular intensity pulsations are accompanied by more complex pulsations in the optical phase. Intensity measurements of far-IR bidirectional ring lasers using the 81- and 153-μm lines in NH₃ find many similar pulsation patterns. Heterodyne measurements of the field amplitude of the FIR laser permit reconstruction of the optical phase in real time and reveal that similar optical frequency shifts occur. More complex and smoothly varying frequency changes accompany the more complex pulsation patterns. The remarkable similarity between the far-infrared laser behavior and the results of the model for lasers with adiabatic elimination of the polarization dynamics suggests that the fundamental dynamic behavior of the bidirectional ring laser may be captured by a reduced set of dynamic equations even when an adiabatic elimination cannot be directly justified from first principles.

© 1988 Optical Society of America