Femtosecond filamentation in water studied by the interference of supercontinuum

Abstract

Supercontinuum (SC) generation is a typical nonlinear phenomenon that occurs during femtosecond filamentation in transparent media. The interference of the SC induced by femtosecond filament in water is explored by using interferometry with the aid of a Mach-Zehnder interferometer (MZI). In the low pulse energy case (single filament is formed), the MZI is used to precisely determine the actual value of filamentation threshold P_{th}. It is found that the value of P_{th} is much higher than that of the critical power for self-focusing P_{cr}. In the higher pulse energy case, by blocking one arm of the MZI, self-interference resulted from SC emitted by femtosecond filaments is studied. By analyzing the interference patterns, we can acquire information on femtosecond filament, such as filament number and filament spacing. The energy range for the generation of single, double and triple filaments in water is also determined. Diffraction effect will distort and even mask the interference patterns, and to eliminate its influence on the results, the spectral signals at shorter wavelength are selected. This work provides an effective approach to study the complex femtosecond filamentation process intuitively and conveniently.

Conical Emission Induced by the Filamentation of Femtosecond Vortex Beams in Water

“…Water is chosen as the medium in this paper because it can generate stable, ultrabroad, high-intensity supercontinuum at a low cost, standing out among the condensed state media to generate supercontinuum. The critical power for self-focusing 2 0 0 2 cr = 3.77 8 P λ / πn n (the linear and nonlinear refractive index of water are n0 = 1.33 and n2 = 4.1 × 10 −16 cm 2 /W) in water for 800 nm pulse is Pcr = 1.761 MW [33], which is much lower than the filamentation threshold due to the strong dispersion effect [34]. In our previous work, the dependence of the filamentation threshold on the TC in the case of the LG beam was studied by interferometry [26].…”

“…The divergence angle brought by the plano-convex focusing lens takes continuous values between 0 • and 3.8 • . According to the focal length of the selected focusing lens, the focusing regime can be divided into linear and nonlinear ones [35], which greatly affects the femtosecond laser filamentation process and the accompanied nonlinear phenomena like fluorescence and supercontinuum radiation [34,36].…”

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

“…Considering that this study is a more in-depth study based on the work described in Ref. [38], the same experimental device deployed for that study was adopted for this one. See Ref.…”

“…By detecting the typical nonlinear phenomena accompanying femtosecond filamentation, information about femtosecond filamentation can be deduced. Based on this principle, we used a Mach-Zehnder interferometer (MZI) in our previous work to investigate the interference of SC and determined the actual value of P th in the water [38]. The SC that we regard as a coherent light source is induced by femtosecond filamentation and the spectral signal passing through the MZI, resulting in the formation of interference patterns.…”

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

“…Since direct observation of femtosecond filaments in liquid media is not very convenient, it is often necessary to use other methods to diagnose filaments in experiments. In our previous work, by utilizing the interference of the SC induced by femtosecond filament, the actual value of filamentation threshold is determined by the Mach-Zehnder interferometer [31]. The SC generated by femtosecond filament in the transparent medium can be used as a coherent light source, after the spectral signal passes through the MZI, the interference patterns can be formed.…”