Pseudo mode-locking

During the last decade, self mode-locking and resulting comb formation have emerged from a controversially discussed anomaly to a hot topic in semiconductor laser physics. Initial experimental reports claimed mode-locking in a cavity lacking the stabilizing action of a saturable absorber [1] . These reports were heavily disputed as coherent artifacts [2] , [3] , i.e., an erroneous interpretation of autocorrelation measurements of a multimode continuous wave laser. While this incorrect interpretation may explain some peculiar reports, there are numerous indications that there really is a mode-locking effect in some other cases. In particular, some experimental reports indicated a threshold-like collapse of the intermode beat linewidth [4] , similar to what is seen in traditional laser mode-locking. Despite numerous attempts to tackle the underlying physical mechanism, it is still not understood how mode-locking can be stabilized without a saturable absorber, defying generally accepted conclusions from the Haus Master Equation [5] . In order to analyze self mode-locking, we rewrote the Master Equation formalism in the frequency domain [6] , converting a partial differential equation into a coupled system of ordinary differential equations.