The random distributed-feedback fiber laser (RFL) is a new approach to obtain a high-power stable supercontinuum (SC) source. To consider both structure simplification and high-power SC output, an innovative structure achieving a kilowatt-level SC output in a single-stage RFL with a half-open cavity is demonstrated in this paper. It consists of a fiber oscillator, a piece of long passive fiber and a broadband coupler, among which the broadband coupler acting as a feedback device is crucial in SC generation. When the system has no feedback, the backward output power is up to 298 W under the pump power of 1185 W. When the feedback is introduced before the pump laser, the backward power loss can be reduced and the pump can be fully utilized, which could promote forward output power and conversion efficiency significantly. Under the maximum pump power of 1847 W, a 1300 W SC with spectrum ranging from 887 to 1920 nm and SC conversion efficiency of 66% is obtained. To the best of our knowledge, it is the simplest structure used for high-power SC generation, and both the generated SC output power and the conversion efficiency are highest in the scheme of the half-opened RFL output SC.

A novel approach of beam cleanup based on stimulated Brillouin scattering with a large core fiber is proposed to improve the laser beam quality. The fusion splice scheme from a single-mode fiber to a very large core fiber (105 µm) is first employed in stimulated Brillouin scattering to steadily excite the fundamental mode of the Stokes beam. As a result, the output beam achieves a measured M2 value of around 1.3 meanwhile the pump conversion efficiency is up to 90%, which is the best in the reports of stimulated Brillouin scattering cleanup to our knowledge.

Multi-coaxial relativistic backward wave oscillator that generates the beating wave of high power microwave pulse driven by a single accelerator and a single guiding magnet system is presented. Making use of the coaxial annular cathodes that can synchronously produce three annular beams at one shot, the average power of 5.88 GW consisting of two frequency components 9.0 and 9.7 GHz is obtained under the diode voltage and current 724 and 19.57 kA, corresponding to the conversion efficiency 41.5%. The conversion efficiency and the beating frequency are considerably stable with the diode voltage. The coaxial transmission supporter developed from our previous experimental research is employed to conductively connect the coaxial structure and to incoherently combine the microwave pulse of two frequencies with little reflection. It is found that the equipotential connection of the coaxial structure modifies the field distribution in the diode structure to facilitate the operation of the coaxial annular cathodes. The coaxial cathodes of different lengths are proved to be efficient at depressing the space charge effect in order to prevent the explosive emission of the inner cathode from being shielded by the outer annular beams.