Numerical Investigation on the Influence of Water Vapor Ionization on the Dynamic and Energy Deposition of Femtosecond Ultraviolet Laser Filamentation in Air

Qingwei Zeng,Ming Chen,Kejin Zhang,Taichang Gao,Lei Liu,Shuai Hu,Chensi Weng

doi:10.3390/app9204201

Abstract

The effects of water vapor ionization on the nonlinear propagation of femtosecond laser pulses with a 248 nm wavelength are numerically investigated in this paper. It is found that ionization of H2O molecules plays a significant role in air ionization, which seriously affects the dynamic and energy deposition of filamentation. The propagation of femtosecond pulses in air with different humidity levels are compared. The total number of electrons and total deposited pulse energy increase with the humidity increases. However, they tend to be saturated in high humidity conditions. Results presented here are conducive to characterizing the long-range propagation of filaments under atmospheric conditions.

Highlights

We numerically investigate the influences of ionization of water vapor on nonlinear propagation of ultraviolet (UV) filaments
To investigate the propagation dynamics of a femtosecond pulse in a gas medium, we modeled the propagation of a laser pulse with the nonlinear Schrödinger equation (NLSE), which governs the evolution of the electric field envelope E(x,y,z,t) of the pulse in the reference frame moving at the group velocity v g = ∂ω/∂k ω [9]: X
TheThe results show thatthat clamping intensity and and electron density are very in dry humid conditions

Summary

Introduction

Investigation of the formation of light filaments in air has become a topic of active experimental and theoretical research due to their various potential atmospheric applications, such as remote sensing of chemical/biological agents [1] and meteorological elements [2], high-voltage discharge guiding [3], air waveguiding [4], and weather-related applications [5,6,7]. Influences of water vapor on multiple physical effects during the filamentation process are expected to be very different when a laser pulse wavelength increases [15]. Only a few studies have considered the influence of relative humidity on the propagation of femtosecond pulses. Simulation studies showed that physical effects like dispersion and linear absorption become more and more important in the formation and propagation dynamics of 10 μm filaments with the increase of relative humidity [15]. Shutov et al [17] experimentally identified that the photoionization of water vapor acts as the dominant ionization process in atmospheric air for femtosecond laser pulses at a 248-nm central wavelength and the relevant ionization coefficients were measured.

Methods

Results and Discussion

Evolution

Conclusions