50W CW visible laser source at 589nm obtained via frequency doubling of three coherently combined narrow-band Raman fibre amplifiers
Luke R. Taylor, Yan Feng, and Domenico Bonaccini Calia
Optics Express, Vol. 18, Issue 8, pp. 8540-8555 (2010) doi:10.1364/OE.18.008540
Abstract: We demonstrate the cascaded coherent collinear combination of a seed-split triplet of 1178nm high-power narrow-band (sub-1.5MHz) SBS-suppressed CW Raman fibre amplifiers via nested free-space constructive quasi-Mach-Zehnder interferometry, after analysing the combination of the first two amplifiers in detail. Near-unity combination and cascaded-combination efficiencies are obtained at all power levels up to a maximum P1178 > 60W. Frequency doubling of this cascaded-combined output in an external resonant cavity yields P589 > 50W with peak conversion efficiency η589 ~85%. We observe no significant differences between the SHG of a single, combined pair or triplet of amplifiers. Although the system represents a successful power scalability demonstrator for fibre-based Na-D2a-tuned mesospheric laser-guide-star systems, we emphasise its inherent wavelength versatility and consider its spectroscopic and near-diffraction-limited qualities equally well suited to other applications.
This work was to demonstrate the scalability of the Raman fiber amplifier approach. As one can imagine, we had worked hard to break the published record power of 50 W by the Starfire people. 🙂