Influence of femtosecond laser repetition rate on sideways scattering of supercontinuum in liquids

We systematically investigated the sideways scattering characteristics of the supercontinuum generated by a femtosecond laser in transparent media, focusing on the influence mechanism of the laser repetition rate. This study aims to elucidate how cavitation bubble dynamics, modulated by the laser repetition rate, regulate the sideways scattering of the supercontinuum during filamentation in liquids. Through experiments using an 800 nm femtosecond laser in methanol and water, we quantitatively analyzed the scattering patterns at 45° and 90° sideways directions from the geometric focus within the 0-1000 Hz repetition frequency range. Experimental results show that at low energy (22.5 μJ), scattering intensity increases monotonically with repetition frequency; while at medium-high energies (213 μJ, 2136 μJ), bubble accumulation effects lead to non-monotonic changes characterized by initial enhancement followed by attenuation. When the frequency reaches 1000 Hz, excessive bubble density in the self-focusing region causes sideways signal attenuation to nearly zero. Mechanism analysis reveals that the dominant factor of sideways scattering shifts from "focus-point scattering" to "pre-focus scattering and loss" with increasing energy. Crucially, similar patterns observed in distilled water confirm the universality of this physical mechanism. This study provides an important experimental basis and theoretical support for the active regulation of supercontinuum and optimization of its application efficiency.