High conversion efficiency, high power density Q-switched fiber laser

An acoustic-optic Q-switched all-fiber laser with a high-repetition-rate, a short pulse width, a wide spectrum, and a high conversion efficiency is experimentally demonstrated. In the laser configuration, a (1+1)×1 side-pumping coupler is introduced to perform backward pumping, and a 10/130-um Yb fiber is adopted. The acoustic-optic component operates in the first direction, achieving a Q-switched pulse with a repetition rate adjustable in the range of 20 kHz-80 kHz. Under a repetition rate of 20 kHz and a pump power of 6.76 W, the fiber laser obtains a highly efficient and stable pulse output, with an average power of 4.3 W, a pulse width of 56 ns, a peak power of 3.83 kW, and a power density of 1.39×10¹⁰ W/cm². Particularly, the optic-optic conversion efficiency of the laser reaches as high as 64%. Another feature of the pulsed laser is that the high reflection mirror reflects the pump light as well, which brings the secondary absorption of the pump power into the gain fiber.