50 Femtosecond Pulse Generation from a Self-Starting c.w. Passively Mode-Locked Cr:LiSrAlF6 Laser

Femtosecond laser physics has been transformed by the advent of the titanium-doped sapphire laser which has been been mode-locked by conventional and novel means [e.g. 1-6], yielding pulses as short as 30 fs [5]. The observation of self-mode-locking [2] has led to the realisation that the nonlinear refractive index of the laser medium can be used to provide both amplitude modulation, through self-focussing or "Kerr Lens Mode-locking" [3], and phase modulation which, together with group velocity dispersion, can lead to further pulse compression. These pulse compression mechanisms are not restricted to Ti:sapphire but will work with any nonlinear medium in the laser cavity [4], We present here the observation of sub-100 fs pulse generation for the first time from a Cr:LiSrAlF6 laser.