Onset of subcritical bifurcation in a CO2 laser with feedback

We report evidence of a subcritical pitchfork bifurcation in the operation of a CO2 laser with feedback for increasing feedback strength. The feedback consists in controlling the cavity losses with a signal proportional to the laser output intensity. The experimental results can be explained by means of a linear stability analysis in the framework of a two level model for the laser. A numerical simulation is also presented