Supercontinuum generation by co-filamentation of two color femtosecond laser pulses

Abstract

In this paper, we experimentally investigate supercontinuum generation via collinear two-color filamentation in sapphire crystal, by launching two femtosecond pulses at fundamental (1030 nm) and second harmonic (515 nm) wavelengths from an amplified Yb:KGW laser. By changing the time delay between the incident pulses, we observe dramatic changes in the supercontinuum spectrum, transmitted energy, position of the nonlinear focus and intensity distribution along the filamentinduced luminescence traces. In particular, we show that at some delays the two pump wavelengths can assist each other in generating supercontinuum, whilst at other delays large portions of the supercontinuum spectrum are completely extinguished. The transition between supercontinuum generation and its extinction occurs within a very short (20 fs) span of the delay times, despite the fact that the pump pulses are 220 fs long. We propose that the observed non-trivial spectral dynamics can be interpreted by a mechanism, where co-propagating two pump pulses perturb the nonlinear refractive properties of the medium via Kerr effect and generation of free electron plasma thereby affecting pulse splitting and pulse front steepening, which are the key players in the process of supercontinuum generation in a normally dispersive medium.

Supercontinuum Induced by Filamentation of Bessel-Gaussian and Laguerre-Gaussian Beams in Water

“…SC has a wide range of applications, such as time-resolved excitation and absorption spectroscopy [45], optical pulse compression [46] and the characterization of laser-induced structural transitions [47], etc. The SC generation induced by femtosecond laser in water has been extensively studied in the past few decades, both experimentally and theoretically [39,[48][49][50][51][52][53][54][55][56]. Quite a few approaches are used to study the property of the SC and to control the SC generation [39,[48][49][50][51][52][53][54][55][56].…”

“…The SC generation induced by femtosecond laser in water has been extensively studied in the past few decades, both experimentally and theoretically [39,[48][49][50][51][52][53][54][55][56]. Quite a few approaches are used to study the property of the SC and to control the SC generation [39,[48][49][50][51][52][53][54][55][56]. For example, the coherence of the SC can be studied by the interference method [39,52].…”

“…By manipulating the parameters of femtosecond laser pulses (such as spatial distribution of intensity [48,49], polarization [50] and pulse energy [51], etc. ), doping the water with other matters [53,54], adopting a twocolor scheme [56], the SC generation can be enhanced. However, these works mainly dealt with Gaussian pulses.…”

High power supercontinuum generation by dual-color femtosecond laser pulses in fused silica

“…[14] Furthermore, they obtained the SC generation from collinear two-color filamentation in sapphire crystal, and also found that the transition between SC generation and its extinction will occur in a narrow delay region. [15] However, the output energy of the spectral enhanced SC is still limited to the level of µJ. In this work, by using an MLA, a mJ level SC with a very broad spectral range is obtained from the dual-color femtosecond filament array in fused silica.…”

Femtosecond filamentation in water studied by the interference of supercontinuum

“…For example, Wang et al found that doping water with silver-nanoparticles can enhance the nonlinear optical response of water, leading to broadening of SC spectra induced by femtosecond filament [34]. Besides, polychromatic field scheme is another effective method to enhance the SC emission [37,38], for example, Vengris et al used two femtosecond pulses at 1030 nm and 515 nm wavelengths to irradiate the sapphire crystal, and by changing the time delay between the two pulses, they observed dramatic changes in the SC spectrum [37]. In effect, the polychromatic field scheme essentially belongs to the first approach, i.e., changing the property of femtosecond laser pulses.…”