Femtosecond KCl: Li and RbCl:Li color-center lasers near 2.8 μm with a HgCdTe multiple-quantum-well saturable absorber

We have used HgCdTe multiple-quantum-well saturable absorbers to passively mode lock KCl:Li and RbCl:Li color-center lasers and have generated pedestal-free pulses as short as 120 fsec near 2.8 μm. To our knowledge, these are the shortest pulses in this wavelength range, and our laser is the only direct source of subpicosecond pulses in the mid-infrared region. Our results generalize the semiconductor passive mode-locking technique to different wavelength ranges, saturable absorber materials, and laser systems and are consistent with a model in which LO phonon collisions determine the fast saturable absorber behavior.