Self-starting femtosecond mode-locked Nd:glass laser that uses intracavity saturable absorbers

We produced transform-limited pulses as short as 130 fs with 160-mW average output power from a passively mode-locked Nd:glass laser. This is to our knowledge the first demonstration of an intracavity semiconductor antiresonant Fabry–Perot saturable absorber continuously starting a Kerr-induced passively mode-locked laser. The antiresonant Fabry–Perot saturable absorber, even with dispersion compensation, produced only picosecond pulses, and femtosecond performance was observed only with the addition of an intracavity long-pass wavelength filter. We propose a new mode-locking mechanism, which we refer to as Kerr-shift mode locking, in which the wavelength-dependent intracavity aperture and self-phase modulation in Nd:glass combine to produce a self-wavelength shift that reduces intracavity losses for femtosecond pulses.