Excess noise in intracavity laser frequency modulation

The response to perturbations and to stochastic noise of a laser below thre shold subjected to an intracavity periodic frequency modulation is theoreti cally studied. It is shown that, when the modulation frequency is close to the cavity axial mode separation but yet detuned from exact resonance, the laser exhibits a strongly enhanced sensitivity to external noise, which inc ludes large transient energy amplification of perturbations in the determin istic case and enhancement of field fluctuations in presence of a continuou s stochastic noise. This large excess noise is due to the nonorthogonality of Floquet laser modes which makes it possible continuous energy transfer f rom the forcing noise to transient growing perturbations.