ANOMALOUS RESPONSE OF A SINGLE-MODE FREQUENCY-MODULATED LASER AT THE LINE CENTER

We show numerically that a single mode laser that is frequency modulat ed for resonance at the line centre exhibits extremely weak small sign al response compared to off-resonance cases where modulation frequenci es are integer fractions of the line centre relaxation oscillation fre quency. In fact in some cases the response rises by as much as two ord ers of magnitude. Thus an instability is indicated here for the first time with realistic values of the modulation index.