Improving the Laser Performance of Yb^3+-Doped Phosphate Fiber: Population Simulation of the Yb^3+ Level

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.

Keywords

• $^{3+}$ -doped phosphate fiber%22%2C%22default_operator%22%3A%22AND%22%7D%7D%7D"> Yb<named-content xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" content-type="math" xlink:type="simple"> <inline-formula> <tex-math notation="LaTeX">$^{3+}$</tex-math> </inline-formula> </named-content>-doped phosphate fiber
• numerical simulation
• Boltzmann distribution
• Multi-phonon relaxation probability criterion