Design, performance, and limitations of fibers for cladding-pumped Raman lasers

In this paper, we present basic design rules for double-clad fibers that enable efficient 1st-Stokes operation of cladding-pumped fiber Raman devices. Limiting factors that we treat include unwanted 2nd-Stokes generation, material damage in the core, pump pulse dispersion, inner-cladding NA, background loss, pulse shape and pump noise. With a well-designed fiber, we calculate that a pump-to-signal brightness enhancement of over 2000 is possible, with certain pump parameters. On experimental work, we report a 100 W cladding-pumped fiber Raman laser at 1120 nm. Furthermore, a double-clad Raman fiber with large-mode area, ∼40 μm core diameter, pumped by a Q-switched Nd:YAG laser is used to generate Stokes pulses with 1 mJ energy.