Amplification of near-resonant signals via stochastic resonance in a chaotic CO2 laser

We show experimentally and numerically that a chaotic CO2 laser with modulated losses operating in the region of an intermittency resulting from the band-merging crisis can serve as an amplifier of near-resonant signals, i.e., signals with a frequency close to the first subharmonic frequency, via deterministic stochastic resonance. The mechanism underlying stochastic resonance in this case is a synchronization of the random switching events between two chaotic repellers after the band-merging crisis with near-resonant signals at the detuning frequency. We demonstrate experimentally that the gain factor in chaos is larger than near the first period-doubling bifurcation by a factor of 2. Numerical results obtained in a two-level rate-equation model are in good agreement with the experimental ones.