The response of a CO2 laser with losses modulated at frequency Ω to a loss perturbation of frequency Ω/2 as well as the response at the idler frequency is investigated experimentally and numerically near the onset of a period-doubling bifurcation under conditions in which the relaxation oscillation frequency of the CO2 laser is larger than Ω. Strong amplification of the perturbation signal below the bifurcation point and deamplification above it have been observed. We have found that the laser response depends on the amplitude and phase of the perturbation signal and that the maximum amplification is proportional to a certain power of the perturbation amplitude which, for the parameters used, is -0.6. We show that the idler-to-signal ratio decreases with increasing perturbation amplitude. Reasonable agreement between numerical and experimental results has been obtained. © 1995.