Analysis of laser polarization state on remote induced plasma luminescence characteristics of filament in air

TL;DR

This study investigates how the polarization state of femtosecond laser filaments affects the fluorescence emission of nitrogen molecules at 30 meters, revealing that linear polarization yields stronger signals than circular polarization, with implications for remote sensing.

Contribution

It provides a detailed analysis of the influence of laser polarization on plasma fluorescence during long-range filamentation, including the underlying mechanisms involved.

Findings

Linear polarization produces higher fluorescence signals than circular polarization.

Polarization affects the critical power for filamentation and plasma emission mechanisms.

Results enhance understanding of remote sensing applications using laser filaments.

Abstract

The femtosecond laser filamentation is the result of the dynamic interplay between plasma self-focusing and defocusing generated by the multiphoton/tunnel ionization of air molecules. This equilibrium allows the filament to stably propagate over long distances at high power densities, making it a promising tool for remote sensing in chemical and biological applications, detection of air pollution, and lightning control, which has attracted wide attention. Laser-induced filamentation is a highly nonlinear process, and initial conditions such as changes in polarization state can affect the fluorescence emission of N2 molecules excited by the filament in air. In this article, we analyze in detail the effect of polarization state changes on the 337 nm fluorescence signal excited by the filament at a distance of 30 m. It was found that the fluorescence signal intensity of the linear polarization state was higher than that of the circular polarization state. Through analysis of these phenomena, we explore the mechanism of plasma fluorescence emission during the long-range filamentation process of femtosecond laser, including the electron collision model and the polarization effect on the critical power for filamentation. These findings are important for the understanding of the stimulated radiation from filaments and may find applications in remote sensing of electric field and THz radiation.