Bleaching effect of radiation-induced darkening in Yb-doped large mode area photonic crystal fiber based on deuterium and hydrogen loading.

We report the radiation-induced darkening (RD) effect caused by X-ray radiation and the bleaching effect caused by D/H/N loading in self-developed Yb-doped large mode-area photonic crystal fibers (LMA PCFs). The decrease in the slope efficiency caused by irradiation decays exponentially with an increase in the X-ray radiation doses, and the radiation-induced gain variation (RIGV) showed a linear decay trend with increasing irradiation doses. The slope efficiency of Yb-doped LMA PCF, which significantly degraded from 71.00% to 50.42% after 50 Gy irradiation, can be significantly restored after D loading to 97.21% of the slope efficiency of pristine fiber. However, the slope efficiency of the PCF loaded by H can be recovered to 88.54% that of the pristine. These results suggest that D loading has a more pronounced bleaching ability than H, while N does not exhibit any bleaching effect. Based on the all-fiber modular amplification experiment, an average amplified output power of 41.4 W at the pump power of 62.3 W was achieved from Yb-doped LMA PCFs irradiated with 50 Gy followed by D loading. The slope efficiency (with respect to the pump power) was 69.05%, with the laser beam quality factor M of 1.2. No obvious power decaying of the laser output was observed for about 10 h. RD and bleaching effects of the Yb-doped LMA PCF core glass have been thoroughly investigated using the absorption, radiation-induced attenuation (RIA), continuous wave electron paramagnetic resonance (CW-EPR), emission, Raman, and Fourier transform infrared (FTIR) spectra.