Stabilizing or destabilizing lasers by continuous delayed feedback

The equations for a class B laser with loss modulation and delayed feedback have been analysed. By using asymptotic methods, an amplitude equation is determined which describes the first period doubling bifurcation. From this equation, it is shown that the feedback may stabilize an initially unstable periodic solution by shifting the period doubling bifurcation point. However, we also show that the feedback may destabilize an initially stable periodic solution for different values of the parameters. Our results are substantiated by a numerical study of the laser equations and by new experiments on a CO 2 laser.