Abstract
Based on the Boltzmann distribution and multi-phonon relaxation probability criterion, an original Yb3+ population equation was proposed to describe the population distribution before and after laser generation, and the population distribution of Yb3+ under different pump ratios and temperatures was investigated by numerical simulation. The simulation results indicated that the laser wavelength of Yb3+-doped modified phosphate fibers have a high probability of being in the range of 1019 nm--1056 nm under the conventional pump ratio. Additionally, fibers lasing at a longer wavelength may have a lower laser threshold. For ultra-high pump ratio or high fiber temperature, the laser operation state changes from a quasi-four-level to a quasi-three-level scheme, and the laser wavelength may blue-shift. Experimental results verify the above simulation results, and in addition demonstrate an output power of 9.38 W with a slop efficiency of 27.4% in an Yb3+-doped phosphate modified fiber with a length of 35.4 cm and diameter of 280 μm from an optical path with a refrigeration patch and suppressing short-wave laser output. The results show that the laser performance of Yb3+-doped fibers can be improved by reducing the operating temperature and inhibiting short-wave laser output.
Highlights
IntroductionThe common way is to modify the phosphate glass network, changing the field strength and symmetry of Yb3+, and enhance the Stark splitting of Yb3+: 2F7/2 level, such as adding F-ion (Stark splitting from 589 cm-1 to 716 cm-1) [15], alkaline earth metal oxides (Stark splitting from 499 cm-1 to 589 cm-1) [16], SiO2 (Stark splitting from 605 cm-1 to 808 cm-1) [17], and GeO2 (Stark splitting from 627 cm to 815 cm-1) [13], so as to improve the performance of lasing material
It is difficult to obtain laser output from Yb3+-doped phosphate glass [13], and only 2.7 W laser output can be obtained in Yb3+-doped phosphate fiber [14]
In this paper, based on the Boltzmann distribution and multi-phonon relaxation probability criterion, an original Yb3+ population equation was proposed to describe the population distribution before and after laser generation, and the relationship between the population distribution of Yb3+, p, and temperature was investigated by a numerical simulation method
Summary
The common way is to modify the phosphate glass network, changing the field strength and symmetry of Yb3+, and enhance the Stark splitting of Yb3+: 2F7/2 level, such as adding F-ion (Stark splitting from 589 cm-1 to 716 cm-1) [15], alkaline earth metal oxides (Stark splitting from 499 cm-1 to 589 cm-1) [16], SiO2 (Stark splitting from 605 cm-1 to 808 cm-1) [17], and GeO2 (Stark splitting from 627 cm to 815 cm-1) [13], so as to improve the performance of lasing material. The simulated results were verified by changing the resonator and the use of an additional refrigeration patch in an optimized Yb3+-doped phosphate fiber, which aim is to determine some methods to improve the laser.
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