Thermal effect model of gain medium in multipulse picosecond laser

High-power picosecond lasers have a wide range of applications in high-precision drilling, solar cell cutting, and ultrafast spectroscopy. The main oscillator power amplifier (MOPA) technology is an effective scheme to generate high-power picosecond pulses. The thermal effect of the laser gain medium significantly impacts both the laser power output and beam quality. This paper prioritizes constructing a thermal effect model of the gain medium and simulates the temperature field distribution inside the crystal under different pumping modes. Then the pulse string picosecond laser output was successfully realized using the self-developed picosecond fiber seed laser and a two-stage end-face pumped traveling wave amplifier. The maximum average output power of 26.1 W, 28 W, and 29.6 W was obtained when the pulse string contained 2, 5, and 10 sub-pulses, respectively, corresponding to pulse energies of 130.5 µJ, 140 µJ, and 148 µJ at a repetition rate of 200 kHz.