Hysteresis in highly overdriven additive pulse modelocked laser systems

Additive pulse modelocking (APM) is a popular technique for passive modelocking of solid state and fiber lasers. Recently, a number of systems have been demonstrated in which the nonlinearity in the auxiliary cavity (AC) is much higher than that assumed in conventional APM theory. Effects such as period doubling, multiple π nonlinear phase shift in the AC, etc., have been observed. In this paper we describe experiments performed on an APM NaCl:OH^- color center laser and an extension of an APM theory that sheds some light on these highly nonlinear systems. In particular, we show a novel hysteresis in this laser and explain the underlying physics