Abstract

Single-crystal fibers offer a great potential as low threshold miniature laser sources. This paper illustrates this potential by reporting the characteristics of Nd:YAG fiber oscillators. Fibers were grown by the laser-heated pedestal growth technique. They were made into lasers by (1) mounting several 60-250-µm diam, 5-15-mm sections in a holder for polishing purposes, (2) polishing and AR coating the ends, (3) placing the fibers in a flat mirror external cavity, and (4) end pumping a fiber through the back mirror with the focused beam of a cw Ar-ion laser (λ = 514.5 nm). Continuous-wave oscillation at 1.06 and 1.32 µm is demonstrated in over forty fibers, either in a guided or unguided mode. Thresholds as low as 3.5 mW and conversion efficiencies up to 31 % are observed, with output powers as high as 30 mW. Q-switched 1.06-µm fiber lasers are also demonstrated by mechanically vibrating the back mirror. A typical device output is 70-ns, 50-mW pulses at a 4-kHz rate. The mechanism responsible for residual fiber loss is scattering induced by fiber diameter variations (1-10%). Future devices made of fibers with improved diameter control (-“0.1%) should yield further reduction in threshold and the possibility of monolithic devices.

© 1985 Optical Society of America