Double-pass fiber Raman laser-a powerful and widely tunable in the ultraviolet, visible, and near-infrared fiber Raman laser for biomedical investigations

We present the operating principle, general features, and advantages of a novel concept for the development of powerful and widely tunable fiber Raman lasers (FRL´s), based on the high-power pumping of large-core low-loss multimode fibers using a simple double-pass laser arrangement with Littrow-prism-tuned emission. Basic experimental results obtained with various modification double-pass FRL schemes, which provide the generation of both discretely tunable emission in the UV/blue (360-493 nm) at λ_p=355 nm and continuously tunable emission in the visible/near-IR (0.54-1.01 μm) at λ _p=532 nm, are reported. The double-pass FRL schemes permit powerful and widely tunable spectral components to be generated, due to the double passing of nonlinear-converted laser emission through the optical fiber, maximum cavity feedback, the use of multimode fibers, and high-power pumping