Study on mid-infrared optical parametric oscillator based on MgO:PPLN pumped by narrow linewidth 1064 nm fiber laser

A 3.83 μm mid-infrared optical parametric oscillator based on 1064 nm Yb-doped fiber laser pumped MgO:PPLN is proposed. Based on the threshold theory of single resonant optical parametric oscillator and the beam energy concentration theory before and after linewidth narrowing, the effects of the beam distribution in the resonant cavity and the different energy concentration levels before and after linewidth modulation on the threshold and optical-optical conversion efficiency under different pump beam focusing depths are analyzed. By using a single fiber Bragg grating to narrow the pump light width, the influence of the pump light width on the output characteristics of the mid-infrared optical parametric oscillator is analyzed under different duty ratios. When the pump power is 18 W, the pulse laser duty cycle is 0.2%, the pulse width is 100 ns, and the pump light width is 2.5 nm, the MgO:PPLN mid-infrared optical parametric oscillator obtains 3.83 μm laser output with a power of 1.42 W, and the optical-optical conversion efficiency is 7.9%. When the linewidth is narrowed to 0.1 nm and the pulse width is 2 ns, the infrared optical parametric oscillator in MgO:PPLN achieves 3.83 μm laser output with the highest power of 1.98 W. The optical-optical conversion efficiency is 11% and the beam quality M²=1.89. At the same time, the laser output efficiency is increased by 39.2% compared with that before linewidth narrowing.