Analysis of Pulse Broadening Properties of Few-Cycle Laser Pulses in Nonlinear Crystals

Due to the extremely ultrashort pulse width and broad spectral bandwidth, few-cycle laser pulses are highly susceptible to dispersion effects when propagating in nonlinear crystals, which leads to pulse broadening and waveform distortion. The pulse broadening characteristics of few-cycle laser pulses in β-barium metaborate (β-ΒaΒ₂Ο₄, BBO) crystal and Lithium niobate (LiNbO₃, LN) crystal are analyzed. Through numerical calculations, the second-order dispersion and third-order dispersion of crystals are compared, and then the influences of crystal thickness, pulse oscillator cycles, and central wavelength on the broadening of pulse width are systematically analyzed. The numerical results indicate that the few-cycle laser pulse is susceptible to high-order dispersion due to its wide spectrum. Specifically, second-order dispersion causes symmetric broadening, while third-order dispersion causes asymmetric broadening of the pulse. It is thus necessary to take the third-order dispersion effect into account when studying the propagation of few-cycle laser pulses in crystals. Furthermore, the broadening in the LN crystal is larger than that of BBO crystal since the dispersion coefficient of LN crystal is higher. Fewer oscillation cycles contained in the laser pulse correspond to more significant pulse broadening. In addition, pulse width variation is closely correlated with the central wavelength, and an optimal wavelength exists in the near-infrared band to minimize pulse broadening. The research findings facilitate the understanding of the propagation laws of few-cycle laser pulses in nonlinear crystals and provide a reference for the analysis and regulation of pulse broadening phenomena in strong-field physics experiments.