Abstract

In cases where one of the dynamic variables of single-mode lasers undergoes adiabatic elimination, modulation of pump loss or frequency has been found to be an effective way of enlarging the phase space dimension of these lasers, which in turn lose their stability through a universal route. In CO₂ lasers, in particular, such modulation has been widely used by various researchers, which has led to the observation of a wealth of instability results. When the depth of modulation is very small, the laser intensity describes conventional forced damped oscillatory motion.¹ The impact of modulation on the laser intensity, therefore, shows a resonance at relaxation oscillation frequency of the laser. Indeed the modulation in the neighbor-hood of the relaxation frequency has been used in almost all the works reported to date. Contrary to this, we, however, reported recently that a cw CO₂ laser with predominantely homogeneously broadened transition shows chaotic behavior when the gain is modulated even at a frequency much lower than the relaxation oscillation frequency.² Here we present experimental results showing the existence of resonance at a very low frequency hitherto unknown for CO₂ lasers. This has been confirmed by the measurements made with both gain and frequency modulation.

© 1988 Optical Society of America