Exploring the Femtosecond Filamentation Threshold in Liquid Media Using a Mach–Zehnder Interferometer

Abstract

We experimentally studied the supercontinuum induced by femtosecond filamentation in different liquid media. Using a Mach–Zehnder interferometer, we determined the relative filamentation thresholds (Pth) of these media. Research has shown that the value of the filamentation threshold is greater than that of Pcr (critical power for self-focusing), which can mainly be attributed to the strong dispersion effect. Changing the focal length of the focusing lens affects filamentation dynamics, thereby affecting the measured results regarding the filamentation threshold. With shorter focal lengths, the linear focusing (i.e., geometrical focusing) regime dominates, and the measured values of Pth for different liquid media are almost the same; as the focal length becomes larger, self-focusing starts to play a role, making the values of Pth for different media different from each other. This study presents an efficient method for investigating the femtosecond filamentation phenomenon in liquid media, helpful to provide further insights into the physical mechanism of supercontinuum generation via femtosecond filamentation in liquid media.

An Experimental Determination of Critical Power for Self-Focusing of Femtosecond Pulses in Air Using Focal-Spot Measurements

“…Interestingly, in our recent work [48], we observed a similar transition of laser propagation regimes from self-focusing to filamentation, where we defined two critical powers: one for self-focusing and the other for mature filamentation. Hence, we contend that using just one critical power is inadequate for comprehensively studying the filamentation process in certain cases [33,35,36,48], and it is also reasonable to assign the crossover power as the self-focusing critical power at which the self-focusing effects become evident, which has been used in our recent work and other relevant studies [27,[30][31][32]34,39,48,49,52]. These experimental measurements of critical powers under various conditions by using different methods are of great importance in the field of femtosecond filamentation.…”

“…Recently, by using a pinhole located at a focus region, we obtained experimentally and numerically the critical power for femtosecond filamentation in air [34]. Li and Zhang et al explored the threshold of filamentation in liquid by using interferometry [35,36]. For structured laser beams, the situation becomes more complicated.…”