Spectral Narrowing in Nonlinear Compton Scattering via Chirped Laser Pulses

Spectral broadening due to ponderomotive effects strongly limits the spectral brightness of light sources generated in nonlinear Compton scattering. In this work, we demonstrate within the strong-field quantum electrodynamics framework that the equal-power frequency-chirped laser pulses can significantly suppress the spectral broadening by combining the frequency modulation with temporal pulse extension. The resulted radiation energy is concentrated into a blue-shifted first-order harmonic, with enhanced intensity and near symmetric angular distribution in the electron forward direction. The effcacy of equal-power chirped lasers is also examined in the high-energy regime involving ultra-relativistic electrons and super-intense laser fields. In contrast, the equal-FWHM chirp, although convenient for theoretical studies, provides limited capability to suppress the spectral broadening. Our findings establish the equal-power chirp as a practical and experimentally accessible method for spectral narrowing, offering an easy and viable route to enhance the spectral brightness of laser-driven Compton sources for generating narrow-band X-rays and γ-rays.