High-spectral-purity random Raman fiber laser oscillator with full-open cavity counter-pumped by random lasing

Raman fiber lasers with high spectral purity and simple structure are essential for the high-power fiber lasers beyond the conventional emission band of active dopants. In this paper, we demonstrate a compact random Raman fiber laser (RRFL) oscillator with spectral purity of over 99%. The RRFL is generated in a full-open cavity which is counter-pumped by a random ytterbium-doped fiber laser with half-open cavity. They share the same piece of passive fiber to form the cavity, a fiber Bragg grating separates the signal light and pump light for the output. This configuration promises the compactness and high spectral purity of the RRFL. Leveraging the spatiotemporal gain-modulation, the RRFL can provide both continuous-wave output and stable pulsed output through adjusting the pump power. The output laser of continuous-wave operation and pulsing operation exhibits spectral purity of 99.4% and 99.5% around 1134 nm, respectively. This work offers a simple and robust solution for high-spectral-purity Raman fiber lasers of both continuous-wave operation and pulsed operation of hundred-watt level.