Detection of 1.4 μg/m³ Na⁺ in aerosol at a 30 m distance using 1 kHz femtosecond laser filamentation in air

Abstract

An optimized remote material detection scheme based on the laser filament-induced plasma spectroscopy and light detection and ranging (FIPS-LIDAR) is proposed in this work. The elemental composition and concentration of aerosol are measured by FIPS-LIDAR. By focusing the femtosecond laser with a large aperture (Φ41 cm) concave mirror and coaxial fluorescence collection scheme, the remote detection of aerosol in air at μg/m³ level has been realized at a distance of 30 m. The limit of detection for Na⁺ in aerosol droplets is 8 ppm (3 μg/m³ in air), which is the lowest detection limit that has been reported using millijoule femtosecond laser pulse (4.4 mJ). Furthermore, using spectral preprocessing and optimization of the proposed significance of peak (SOP) algorithm, feature peak signals are extracted from weak signals and the limit of detection can be further decreased to 1.4 μg/m³.