SRS-Induced Spatial-Spectral Distortion and Its Mitigation Strategy in High-Power Fiber Amplifiers

Abstract

The spatial-spectral evolution properties of laser beam in the presence of stimulated Raman scattering (SRS) effect have been studied in large mode area (LMA) fiber. With the employment of long/short pass filters, spatial evolution of the signal and Raman light has been studied individually. After the onset of SRS, the simultaneous optimizing of signal light and degrading of Raman light was observed, which has been attributed to the SRS effect of multimode laser beams in LMA fiber. The spectral evolution characteristics indicated that the SRS effect in LMA fiber will trigger other nonlinear effects, mainly inter-modal four-wave-mixing effect and cross-phase-modulation induced modulation instability. Furthermore, the impacts of bending strategy and multimode LMA fiber on SRS-induced spatialspectral distortion have also been studied, which shows that the SRS-induced mode distortion can be suppressed by increasing the fiber size while the bending strategy plays a limited role.

Brightness enhancement on a narrow-linewidth fiber Bragg grating-based master oscillator power amplification fiber laser

“…This abnormal phenomenon has been observed in Ref. [34] To further identify the correlation between beam quality and SRS effect, Figure 7 compares the temporal characteristics at the maximum output power with three different pump conditions.…”

Design and optimization methods towards a 10 kW high beam quality fiber laser based on the counter tandem pumping scheme

“…The low absorption cross-section of Yb ions at the tandem pumping wavelength (e.g., 1018 nm) requires long gain fiber for adequate pump absorption, resulting in a relatively low SRS threshold. Additionally, recent studies have shown that SRS might trigger quasi-static mode distortion [6][7][8] or dynamic mode instability (MI) [9][10][11][12][13] , which could degrade the beam quality and directivity of the fiber laser systems. Therefore, mitigating SRS effect is crucial for tandem pumping towards higher power with good beam quality.…”

Impact of weak end-facet reflections on the SRS threshold of high-power fiber oscillators and amplifiers

“…The SRS effect is physically described as the amplification of spontaneous Raman radiation caused by signal light pumping [4], leading to a decrease in signal power. Furthermore, the SRS effect can also deteriorate the beam quality due to the transverse mode instability (TMI) effect [5,6]. Therefore, effectively mitigating the SRS effect is crucial in the design of high-power single-mode fiber lasers.…”