Color centers as simultaneous active laser media and saturable absorbers

There is a family of color centers and metal ion doped crystals that absorb in the emission region of the neodimium lasers. These centers are in general laser active, usually being pumped in a collinear scheme. They can also be used as saturable absorbers for cw passive Q-switching, but this limits the maximum absorption that can be introduced in the laser cavity thus limiting the maximum gain achievable in the saturable absorber/active pumped medium. By using a coupled cavities scheme we were able to optimize the performance of the pumped medium and obtain CW Q-switched operation by an injection mechanism, the saturable absorber being the unique source of loss for the pump. We coupled an astigmatically compensated KCl: Tl ⁰ (1) color center laser cavity with a Nd laser cavity using both properties of the KCl: Tl ⁰ (1) crystal. We obtained complete Q switching of both lasers with a typical pulse width of 1 μs and a pumping efficiency of the color center laser in the order of 40% achieving a maximum output power of 1.3 W for an input pump power of 3 W from the Nd: YAG Q-switched operation was also tested in this coupled cavities scheme using LiF: F ^-₂ color centers. The obtained pulse widths agree well with a simple theoretical model.