Abstract

Several reports of self-starting additive pulse mode-locking (APM) of solid-state lasers have appeared recently. These include diode pumped Nd:YAG and Ti:Al₂O₃ lasers. The nonlinear cavities used in these experiments were formed by using single-mode optical fibers as the nonlinear medium. The fibers are typically on the order of 1 m in length and, along with the reflector, provide the intensity-dependent reflectivity required to trigger and sustain mode-locked operation. The use of fibers for the nonlinear index medium for APM presents a second exciting possibility of simultaneously frequency doubling and tripling the laser output. This combined process is made possible by the well-known but not well understood phenomenon of second-harmonic generation in germanosilicate optical fibers. Fibers that have been self-prepared or conditioned with seeded preparation have resulted in conversion efficiencies as high as 13% when used outside a laser cavity. We will discuss experiments on a cw Nd:YAG laser, which is passively mode-locked by means of a conditioned germanosilicate fiber external cavity for APM and SHG. The external-cavity reflector is 100% reflecting at 1.06 mm and 90% transmitting at 532 nm. The coupled-cavity laser emits pulses at 532 nm that are shorter than 5 ps.

© 1990 Optical Society of America