ABSTRACT
We demonstrate the rapid photodarkening (PD) phenomenon in Tm-doped fiber (TDF) core pumped by a laser at 1080 nm and the bleaching effect of deuterium (${{\rm D}_2}$D2) on PD TDF. By ${{\rm D}_2}$D2 loading for seven days, the PD-induced excess loss (PIEL) in the visible (VIS) and near-infrared (NIR) region have been largely eliminated, and no degradation was observed within 30 days. PD resistance of the ${{\rm D}_2}$D2 pretreated TDF has been investigated as well. The formation of color centers based on defects and precursors in the silica matrix and the mechanism of ${{\rm D}_2}$D2 bleaching are discussed.
ABSTRACT
The laser performance of a high-power ytterbium-doped fiber amplifier is mainly hindered by the onset of mode instability. In this work, the slope efficiency and mode instability threshold of the ytterbium-doped fiber under various gamma-ray radiation doses have been measured. Experimental results reveal that gamma-ray radiation-induced photodarkening degrades mode instability severely, and gamma-ray radiation-induced mode instability degradation can be partly bleached by hours of pump-light injection. It is shown that gamma-ray radiation-induced photodarkening results in a steep reduction of slope efficiency and mode instability threshold; moreover, the entire irradiated fiber can be partly bleached by hours of pump-light injection and exhibits both time and gamma-ray radiation-dose saturation properties. The experimental results indicate that mode instability mitigation can be partly realized by pump-light injection and implies photodarkening suppression is beneficial for TMI mitigation, which is very promising for the advancement of high-power fiber lasers.
ABSTRACT
We demonstrate the almost complete 2 µm laser power recovery of the gamma-ray-irradiated thulium (Tm)-doped silica fiber under deuterium loading. The optical-optical slope efficiency and the cladding absorption spectra of the Tm-doped fiber with gamma-ray irradiation and deuterium treatment have been measured for comparison. It was found that the slope efficiency of the irradiated Tm-doped fiber could be recovered to 96.1% of the pristine after deuterium bleaching, which significantly degraded from 60.7% to 25.3% after irradiation. Meanwhile, the additional absorption attenuation of the irradiated Tm-doped with D2 treatment completely vanished. Based on the comprehensive comparison of cladding absorption spectra, the probable mechanism of the deuterium bleaching effect on irradiated Tm-doped fiber has also been discussed.
ABSTRACT
Tm-doped fiber laser or amplifier can be applied in varied adverse environments. In this work, we demonstrate the pump bleaching of Tm-doped silica fiber with 793nm pump source under gamma-ray irradiation in the range 50Gy-675Gy. The recovery time, the fiber slope efficiency and the fiber cladding absorption spectra after irradiation and bleaching have been measured. It is found that the recovery time and radiation induce absorption are positively associated with doses, however, the fiber slope efficiency of irradiated TDF and bleached TDF are both negatively correlated with doses. Based on the simulation of the fiber core temperature, the probable mechanism of pump bleaching is also discussed.
ABSTRACT
A GeO2 doped triangular-core photonic-crystal fiber (PCF) is designed and fabricated to allow the generation of a hollow beam through a nonlinear-optical transformation by femtosecond pulses at 1040 nm from a high power Yb-doped PCF laser oscillator. The hollow beam supercontinuum is obtained at far field by adjusting incident light polarization to excite the high order supermode, behaving as a mode convertor. The supercontinuum ranging from 540 to 1540 nm is achieved with an average power of 1.04 W.
