Bulk semiconductor saturable absorber for a NaCl color center laser

Using bulk InGaAsP as a saturable absorber we have passively mode locked a NaCl color center laser to produce transform-limited, pedestal-free pulses near 1.6 μm as short as 197 fs with up to 4.2 kW peak power. Our results simplify the saturable absorber material requirements and prove that excitons are not required for generating subpicosecond pulses. By comparing a dozen samples we find that a minimum band-edge absorbance of 40% is required to generate subpicosecond pulses, although details of the band edge are not critical. In addition, we find stable mode locking always occurs on the long-wavelength side of the laser gain peak.