Fiber Lasers – Advancing the Frontier of High Power Light

During the last two and a half decades fiber lasers underwent a revolutionary transformation in their power from initially operating at Watt level to currently capable of producing multi-kW beams. This enabled a widespread use of fiber lasers in a wide range of industrial and defense applications. These revolutionary advances in power and energy are continuing, mostly along the path of coherent and incoherent combining of multiple fiber lasers, which exploits the advantage inherent in fiber technologies for monolithic integration to achieve compact and robust systems even with a large number of parallel laser channels. This is a particularly promising pathway for scaling powers and energies of ultrashort pulse lasers for driving secondary radiation sources of energetic accelerated electrons and positrons, as well as generating high energy neutrons, protons, gamma rays and high-brightness X-rays, which promise new application areas ranging from fundamental science to material science, biology, medicine, and numerous new industrial uses. This summer school lecture will cover fundamentals of rare-earth doped fiber lasers, will describe numerous innovations that enabled ultra-large core fibers constituting the foundation of high power lasers, will survey state-of-the-art performance of different types of laser systems, and will review recent progress in coherently combined fiber lasers.