Double-ended output near-single-mode quasi-continuous wave monolithic fiber laser

Abstract

Quasi-continuous fiber lasers have a broad application prospect in the industrial field. However, in the current research on quasi-continuous wave (QCW) fiber lasers only the single-ended output structure is used. A double-ended output fiber laser oscillator needs only one resonator to realize two laser outputs. Compared with single-ended output laser, it has a low cost, small volume and high work efficiency. It is expected to achieve higher power laser output through double-ended output beam combining. Therefore, the double-ended output QCW fiber laser is proposed and studied in this paper. The steady-state rate equation establishes a theoretical model of a QCW fiber laser oscillator with two ends, considering the stimulated Raman scattering (SRS) and amplified spontaneous emission (ASE). The output power, time domain and nonlinear effects of this type of laser are simulated. The results show that the overshoot effect caused by relaxation oscillation will produce a large amount of thermal deposition and ultra-high peak power in the fiber. It will reduce the nonlinear threshold and limit the increase of power of the QCW fiber laser. Prolonging the rise time of the pump can effectively suppress the relaxation oscillation and obtain a stable pulse output during the pulse duration. In addition, compared with the single-ended QCW laser, the double-ended output structure changes the energy distribution in the fiber and reduces the accumulation of nonlinear effects in the gain fiber, thus inhibiting SRS. Then, the ytterbium-doped fiber with a core/cladding diameter of 20/400 μm is used to achieve the first double-ended QCW laser output with a peak power of 3 kW. The peak power values at both ends are 1218 and 2220 W, respectively. The values of corresponding beam quality factor <i>M</i>² are 1.34 and 1.27. The optical-to-optical conversion efficiency is about 60%. The pulse width is 100 μs, and the repetition frequency is 1 kHz. This research verifies the feasibility of high power and high beam quality output by double-ended output QCW fiber laser, which provides support for small volume, low cost, high power and high brightness QCW fiber laser. Further breakthroughs in the research and application of high-power fiber lasers are expected to be made by continually optimizing experiments, increasing pump power, and improving the laser’s output power and conversion efficiency.