Woohong Kim1 Shyam Bayya1 Brandon Shaw1 Jason Myers1 Syed Qadri1 Rajesh Thapa3 Charles Askins3 John Peele3 Daniel Rhonehouse1 Steve Bowman1 Daniel Gibson1 Joshep Kolis2 Brad Staddleman2 Jasbinder Sanghera1

1, Naval Research Laboratory, Washington, District of Columbia, United States
3, Sotera Defense Solutions, Herndon, Virginia, United States
2, Clemson University, Clemson, South Carolina, United States

In this paper, we present our recent research effort in developing cladded crystal fibers for high power single frequency fiber lasers. Glass fiber lasers, have been very successful to date, with demonstrations of several kW’s of output power, but they have several intrinsic issues that ultimately limit how much power they can produce. These relate to their low thermal conductivity (~1W/m/K) coupled with low usage temperature (Tg<<1000°C), and low dopant concentrations (<1%), which necessitate the use of long fiber lengths. In addition, for single frequency operation, the high stimulated Brillouin (SB) cross-section of glass leads to SB scattering which limits the achievable power. On the other hand, single crystal fibers based on YAG exhibit reduced nonlinearities such as SB scattering and increased thermal conductivity which allows power scaling to higher average and peak powers than in glass core fiber. If designed correctly, their laser output powers can exceed those of all-glass fiber lasers by more than a factor 10, before nonlinear and thermal issues have a detrimental impact. In this paper, we report on the fabrication and physical/optical characterization of cladded single crystal RE:YAG core fiber with the architectures analogous to those seen in LMA silica fiber for application in high power lasers and amplifiers.