Speaker
Description
High-gain harmonic generation (HGHG) is known to be critically sensitive to residual group-delay dispersion (GDD) and third-order dispersion (TOD) in the seed laser, which distort the temporal profile and degrade the harmonic up-conversion spectrum. The feasibility of the direct-amplification enabled harmonic generation (DEHG) scheme has been experimentally demonstrated [Phys. Rev. Lett., 2025]. In the long modulator of DEHG, the seed is first directly amplified to a long, relatively flat radiation pulse. Owing to the slippage between electrons and radiation, each longitudinal electron slice samples the laser field across many optical cycles, thereby averaging out the fine temporal distortions induced by GDD and TOD. Consequently, the energy modulation is governed by the seed spectral envelope rather than the instantaneous intensity, making the subsequent harmonic bunching highly insensitive to dispersion. In addition, the prolonged interaction length intrinsically homogenizes the transverse modulation distribution across the electron beam, further stabilizing the output. These effects enable DEHG to preserve nearly transform-limited harmonic spectra without the need for precise dispersion compensation, significantly relaxing seed laser requirements and positioning DEHG as a robust, practical route for high-repetition-rate seeded FEL facilities.
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