High-performance electro-optically Q-switched 2-kHz Nd:YAG laser with optimized gradient dopant concentration and thermal effects improvement

Abstract

The thermal effects of the gain medium impose significant constraints on achieving high-power high-beam-quality lasers. Gradient-doped crystals can effectively mitigate thermal effects. We use self-grown gradient-doped crystals, and adopt a combination of multiple strategies including diffusion-bonded end caps, pump beam size optimization, and thermal effects compensation, to mitigate the thermal effects of the crystals under the high-power operation. A high-brightness, high-conversion-efficiency, and high-stability laser output is achieved, with an average power up to 12 W at a repetition rate of 2 kHz using a bonded gradient-doped (0 at.% + 0.17–0.38 at.%) Nd:YAG crystal, which corresponds to a peak power of 882 kW. The beam quality is $M_x^2=1.240$ and $M_y^2=1.251$, and the power instability is 0.31 % (RMS). To the best of our knowledge, this is the highest peak power achieved under near-diffraction-limited conditions for an end-pumped single-rod Nd:YAG laser, with a brightness reaching 5.02 × 10¹³ W/(cm²·Sr).