Chirped-pulse coherent pulse stacking in a Yb-doped fiber laser for high-repetition-rate electron bunch shaping

Coherent pulse stacking provides flexible and stable temporal waveform control of picosecond laser pulses, yet its implementation in ytterbium-doped (Yb-doped) fiber lasers is hindered by the stringent requirement for transform-limited (TL) input pulses. Here, a chirped-pulse coherent pulse stacking scheme based on a Solc filter is proposed and demonstrated for high-repetition-rate pulse shaping in a Yb-doped fiber laser system. A frequency-domain iterative model shows that chirped pulses introduce intrinsic comb-like modulation in stacked pulses, whose period and temperature dependence differ markedly from those of TL pulses, thereby enhancing the tunability of coherent pulse stacking and extending its range of applications. Using an eight-crystal YVO₄ stacking module, we generate flat-top, sawtooth, and elliptical green laser pulses at 1 MHz and 81.25 MHz with maximum average powers of 2.1 W and 6.2 W, respectively, while maintaining strong tolerance to crystal temperature variations. The shaped pulses are applied to a CsK₂Sb photocathode in a DC-SRF-II electron gun to generate electron bunches with an elliptical current distribution, validating the feasibility of the proposed scheme for electron bunch shaping. Overall, these results establish a robust, power-scalable route for high-repetition-rate picosecond pulse shaping in fiber-laser-driven photoinjectors and related accelerator applications.