The 9th International Conference on Matter and Radiation at Extremes (ICMRE2026) ( ICMRE2026)

  High-power picosecond laser sources with good beam quality are of considerable interest for precision processing, laser ranging, and electro-optic applications. In this work, we investigate tapered-fiber amplification and harmonic generation techniques for picosecond lasers. A Yb-doped tapered fiber is employed as the main gain medium to mitigate nonlinear effects and transverse mode instability in all-fiber amplification. Numerical analysis of different pumping configurations indicates that the backward-pumping scheme is more suitable for high-power operation, and thermal simulation is further used to optimize the device layout for improved heat dissipation and long-term stability.

  Based on these results, a high-power tapered-fiber amplification system is developed, consisting of a picosecond seed module, pulse stretching module, repetition-rate selection module, pre-amplifier stage, and tapered-fiber power amplifier. At a repetition rate of 29.3 MHz, an average output power of 104.8 W is achieved under 186 W pump power. The output pulse width is 201.4 ps, and the beam quality factor is measured to be M²=1.44. To better describe pulse evolution in the tapered structure, a dynamic nonlinear-coefficient function is introduced into the transmission model, which improves the analysis of picosecond pulse propagation in tapered fibers.

  In addition, frequency-conversion schemes for high-power picosecond green and ultraviolet lasers are studied. For the ultraviolet system, a third-harmonic-generation model based on the spatial distribution of second-harmonic efficiency is established to determine the optimal conversion condition. Using a hybrid amplification architecture combining disk-regenerative amplification and single-crystal-fiber amplification as the fundamental source, 30.2 W picosecond ultraviolet output with a third-harmonic conversion efficiency of 17.89% is obtained. These results provide a practical route toward high-power, high-beam-quality picosecond laser sources and their efficient wavelength conversion.