To meet the needs of high-power fiber lasers, a new fiber structure called chirally coupled core (CCC) fiber has attracted the attention of researchers all over the world. CCC fiber consists of two cores, one of which is a central core distributed along the axial direction, and the other is a side core that is offset from the central axis and spirally distributed around the central core. Meanwhile, CCC fibers are helical-translation symmetric. The unique structure results in advantages of robust single-mode performance, mode-distortion-free splicing and compact coiling of CCC fiber. Based on a brief description of the theory about CCC fiber, this article focuses on the research progress and application prospect of CCC fiber.

High-power solid-state lasers are among the hot research directions at the forefront of laser research and have major applications in industrial processing, laser-confined nuclear fusion, and high-energy particle sources. In this paper, the properties of Yb:YAG and Nd:YAG crystals as gain media for high-power solid-state lasers were briefly compared, according to the results of which Yb:YAG crystals are more suitable for high-power applications. Then, the effects of the thermodynamic and spectral properties of Yb:YAG crystals with temperature were analyzed in detail, and it was shown that the laser beams amplified by the cryogenically cooled Yb:YAG crystals could have higher beam quality, higher pump absorption efficiency, lower pump threshold, and higher gain. The change in properties of Yb:YAG crystal at low temperature makes it more suitable as a gain medium for high-power lasers. Subsequently, two types of kilowatt-class lasers using cryogenically cooled Yb:YAG crystals as gain media are introduced—100 J, 10 Hz nanosecond lasers and 1 J, 1 kHz picosecond lasers. Their configuration, main parameters, and typical output results were analyzed. Finally, future directions in the development of cryogenically cooled Yb:YAG lasers are discussed.