Objective Diode-pumped solid-state laser(DPSSL) has a large energy compact structure, high efficiency, and good stability, which possesses outstanding application value and prospects in scientific research, military, industrial processing, and other fields. DPSSL has achieved rapid development in the past 10 years. The efficiency of high average-power solid-state laser has been the development direction of solid-state lasers. The planar waveguide gain medium can satisfy the high injected laser and high pump laser intensities. Thus, the planar waveguide laser is one of the potential laser technologies for obtaining high optical-optical efficiency and high average-power output. In this study, a quasi-continuous long pulse width Yb YAG planar waveguide laser amplifier at room temperature with a wavelength of 1030 nm was constructed and the factors affecting the optical-optical conversion efficiency were analyzed. We hope that this study will help improve the optical-optical conversion efficiency of high-power solid-state lasers. Methods The experiment is based on a planar waveguide gain medium. First, the theoretical model of laser dynamics based on Yb YAG was developed. The effects of the injected laser intensity, pump laser intensity, and pump pulse width on the optical-optical conversion efficiency were analyzed through computer simulation. Then, a quasi-continuous long pulse width Yb: YAG planar waveguide laser amplifier at room temperature with a wavelength of 1030 nm was constructed. Next, the output energy of the amplifier was tested to verify the correctness of the theoretical model. The laser amplifier was operated at different pulse repetition frequencies. In addition, the beam quality of the output laser was measured using a beam quality analyzer, and spectra of the output laser were analyzed using a spectrograph. and Discussions The simulation results show that the higher the seed laser power, the earlier it enters the steady-state extraction. The higher the injected laser intensity, the higher the optical efficiency of the steadystate and optical-optical efficiency of the pulse. However, the increase in steady-state optical-optical efficiency decreases gradually (Table 1). With an increase in pump power, the steady-state optical-optical efficiency increases and remains stable. Due to the shortening of power rise time, the optical-optical efficiency of the single pulse increases (Table 2). The output power of the pulse width of 500 tts and output power pulse width of 1 ms are identical in the first 500,is, indicating that the pump pulse width does not affect the time to reach a steady-state (Fig. 6). The time to reach a steady-state is decided by the pump and injection intensities. The pump pulse width is longer, proportion of the time to reach a steady-state in the entire pulse width is smaller, and pulse optical-optical efficiency approaches the steady-state optical-optical efficiency. The theoretical calculation results show that the output energy is 4.96 J and optical efficiency of monopulse is 46.8 %, when pulse width is 500 mu s. The experimental result shows that the output energy is 4.67 J and optical-optical efficiency is 44.0 % (Fig. 7), which is consistent with the theoretical calculation result. The single pulse energy of the laser is not affected by pulse repetition frequency. Thus, the average output power can be linearly increased by increasing the repetition frequency. With the average output power increasing, the beam quality of the output laser gets worse in the Y direction ( Figs. 8-10). The amplified output laser has the same central wavelength as the seed laser, but the linewidth is slightly compressed (Fig. 11). Conclusions In this study, a quasi-continuous long pulse width Yb: YAG planar waveguide laser amplifier at room temperature with a wavelength of 1030 nm is constructed. The effects of injected laser intensity, pump laser intensity, and pump pulse width on the optical-optical conversion efficiency are analyzed. The master oscillator power amplifier is adopted, and the seeder is maintained at a polarization of 1030 nm fiber laser. The gain medium of the amplifier is a Yb YAG planar waveguide, and the pump sources are two quasi-continuous 940 nm laser diode arrays. After shaping, the pump light is coupled into the planar waveguide from the two end facets. With dual end pumping, we obtain the laser amplification output with a maximum energy of 4. 65 J when the pump repetition frequency is 400 Hz, and the maximum peak pump power is 20. 4 kW. The polarization degree is 97%, and the optical-optical conversion efficiency is 44.0%, which is consistent with the theoretical calculation.
