Cascaded Raman Fiber Lasers

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High power fiber lasers have seen tremendous development in the last decade with output powers exceeding 10 kW from a single fiber. This development is fueled simultaneously by industrial and defense applications. This rapid advance in technology has occurred with rare-earth doped fiber lasers, specifically Ytterbium doped fiber lasers at the forefront. The window of emission wavelengths from Ytterbium doped fiber lasers is limited to a small band (1.05–1.1 micron). Other rare-earth doped fiber lasers such as Thulium (1.9–2.1 micron) and Erbium (1.53–1.59 micron) partly complement the emission range, however, are significantly limited in power and efficiency compared to Ytterbium doped fiber lasers. As a result, there are significant white spaces in the wavelength spectrum where rare-earth fiber laser technology is power constrained or completely unavailable. This is a significant constraint since several desirable attributes such as atmospheric transparency and eye safety is lacking in the Ytterbium emission window but is available at other wavelengths. Cascaded Raman fiber lasers are the only known wavelength agile, high power fiber laser technology that can span the wavelength spectrum and cover the white spaces. Cascaded Raman fiber lasers leverage the technology of high power, rare-earth doped fiber lasers (such as Ytterbium) which serve as its input and converting it to any desired wavelength region using one or more wavelength shifts of stimulated Raman scattering in optical fibers. The area of Raman fiber lasers has seen extensive development in the last few years in various fronts such as new laser architectures, scaling output power, improving efficiency, enhancing wavelength diversity, and improved spectral quality. There has also been significant work in novel and niche implementations of Raman lasers. In this chapter, we comprehensively address the technology of cascaded Raman fiber lasers and its many applications, specifically focused on the most recent developments.