Phase-sensitive signal amplification and squeezing near period-doubling bifurcation in a CO₂ laser

The effect of the phase of a perturbation signal at frequency f 2 on the laser response has been investigated in a CO₂ laser with losses modulated at frequency f near a period-doubling bifurcation. Phase-sensitive signal amplification and classical squeezing have been detected and studied both theoretically and experimentally. We have found that phase-sensitive squeezing exists only below the bifurcation point. The squeezing width decreases linearly with increasing bifurcation parameter and the squeezing depth increases with bifucation parameter being 30% at the bifurcation point for the parameters used. We interpret the observed experimental results for zero phase on the basis of the existence of multistability of periodic solutions with the same frequency f 2 as the perturbation signal.