Geoff E. Fair

Predicted performance limits of yttrium aluminum garnet fiber lasers

The effect of various parameters that limit the performance of fiber lasers are calculated for yttrium aluminum garnet (YAG) as the fiber core. The optimum core diameter, the optimum fiber length, and the corresponding output power capability are determined for a variety of optical and structural parameters of YAG, based on available data in the literature to date. It is shown that a conservative limit for YAG fiber laser is 6u2004kW per fiber in multimode operation, compared to 1.8u2004kW for a silica-based fiber laser. Furthermore, it is shown that if stimulated brillouin scattering gain, a key limiting parameter, is <10−12u2004m/W in YAG, as a recent publication suggests, the maximum output power is 30u2004kW per fiber without a significant increase in fiber core diameter. Similar gains are predicted for single-mode operation, although with much lower output power limits. A parametric study shows the relative merits of improving on various optical parameters.

Lasing of surface-polished polycrystalline Ho: YAG (yttrium aluminum garnet) fiber

A polycrystalline 1.5% Ho: YAG fiber with a diameter of 31 µm was prepared. Surface roughness from grain boundary grooving was reduced by polishing, which decreased the fiber scattering coefficient from 76 m-1 to 35 m-1. Lasing tests were done on this fiber with a SF57 Schott glass cladding. Lasing was confirmed by spectrum narrowing with threshold pump power lower than 500 mW and a slope efficiency of 7%. To our knowledge, this is the first lasing demonstration from a small diameter polycrystalline ceramic fiber.