Experimentally determined critical power for self-focusing of femtosecond vortex beams in air by a fluorescence measurement

Abstract

The filamentation of the femtosecond vortex beam has attracted much attention because of the unique filamentation characteristics, such as annular distribution and helical propagation, and related applications. The critical power for self-focusing of the femtosecond vortex beams is a key parameter in the filamentation process and applications. But until now, there is no quantitative determination of the critical power. In this work, we experimentally determine the self-focusing critical power of femtosecond vortex beams in air by measuring fluorescence using a photomultiplier tube. The relation between the self-focusing critical power and the topological charge is further obtained. Our work provides a simple method to determine the self-focusing critical power not only for vortex beams but also for Airy, Bessel, vector, and other structured laser beams.

Numerical simulation study on distinguishing nonlinear propagation regimes of femtosecond pulses in fused silica

“…It is important to note that the obtained 3.8 MW crossover power does not represent the nominal critical power for self-focusing, as the specific value of the crossover power can vary depending on experimental conditions 20 , 23 – 27 . Moreover, directly determining the exact nominal critical power in experiment can be challenging 26 .…”

“…Moreover, directly determining the exact nominal critical power in experiment can be challenging 26 . However, for the purpose of providing clear and referenceable measurements for experimental investigations and practical applications of femtosecond filamentation, in this study, we adopt the crossover power as the critical power for self-focusing, as done in our recent work and relevant literatures 10 , 11 , 20 , 21 , 24 , 28 , 29 .…”

“…The nonlinear propagation dynamics of structured beams are also crucial both for fundamental physics studies and practical applications, such as laser micromachining 14 , laser spectroscopy 15 , air lasing 16 , and optical waveguide 17 . However, the nonlinear propagation characteristics of femtosecond vortex beams which have a donut-shaped intensity profile, differ significantly from those of Gaussian beams 18 – 20 . Specifically, when an intense femtosecond vortex beam propagates in optical media, it undergoes a unique nonlinear evolution.…”

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

“…For example, by using the moving focus method, the value of Pcr in air [26], helium [27] and flame [28] has been measured. Liang et al [29] experimentally determine the value of Pcr for femtosecond vortex beams in air by measuring fluorescence using a photomultiplier tube. Akturk et al [30] proposed a P-scan method to successfully distinguish linear, moving focus, filamentation, and multi-filamentation regimes in gases, and obtained the critical power of femtosecond Gaussian beam.…”

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

“…For example, by using the moving focus method, the value of P cr under air [33], helium [34], and flaming conditions [35] has been measured. Liang et al [36] used a photomultiplier tube to measure fluorescence and experimentally determine the value of P cr for femtosecond vortex beams in atmospheric conditions. Akturk et al [37] proposed a P-scan method to successfully distinguish moving focus, linear, filamentation, and multi-filamentation regimes in gases and obtained the P cr associated with a femtosecond Gaussian beam.…”