Spectral Narrowing in Nonlinear Compton Scattering via Chirped Laser Pulses

Spectral broadening due to ponderomotive effects significantly limits the spectral brightness of light sources generated by nonlinear Compton scattering. In this study, within the strong-field quantum electrodynamics framework, we demonstrate that equal-power frequency-chirped laser pulses can significantly suppress spectral broadening by combining frequency modulation with temporal pulse extension. The resulting radiation energy is concentrated into a blue-shifted first-order harmonic with enhanced intensity and a near-symmetric angular distribution in the electron forward direction. The efficacy of the equal-power chirped lasers was examined in a high-energy regime involving ultra-relativistic electrons and super-intense laser fields. By contrast, an equal-full width at half maximum chirp, although convenient for theoretical studies, has a limited capability to suppress spectral broadening. Our findings establish an equal-power chirp as a practical and experimentally accessible method for spectral narrowing, thus 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.