Abstract

We have recently observed a sinewave self-pulsing in the beam transmitted by a passive cavity containing 2-level molecules, driven by a continuous wave. In this experiment made at a wavelength λ ≅ 3.5 mm, the intracavity Rabi frequency is comparable to the free spectral range ( 830 kHz ) of the very long cavity used (l =182 m) {1} and much larger than the collisional linewidth (≅ 25 kHz) .The medium is then strongly saturated by the driving field ( saturation parameter > 1000) so that its absorption , heavy in the linear regime (αl > 100), is in fact quite moderate. We claim that the self-pulsing observed in these conditions is the first experimental evidence of the multimode instability, predicted a long time ago by Bonifacio and Lugiato {2} but not yet observed. This instability is the multimode counterpart of the single mode instability, recently observed by Orozco et al {3}.

© 1988 Optical Society of America