Particle size distributions and compositions of aerosols produced by near-IR femto- and nanosecond laser ablation of brass

Abstract

Particle size distributions and compositions of primary aerosols produced by means of near-IR femtosecond laser ablation (λ = 775 nm) of brass in He or Ar at atmospheric pressure have been measured. Aerosols were characterized using a 13-stage low-pressure impactor covering a size range from 5 nm up to 5 μm and subsequently analyzed applying total reflection X-ray fluorescence spectrometry. The results indicate, that for femtosecond laser ablation in the low-fluence regime (<5 J cm⁻²) ultra-fine aerosols (mean diameter d_p ≈ 10 nm/peak width w_p ≈ 35 nm) are produced. Furthermore, the total Cu/Zn ratio of these aerosols corresponds to the composition of the bulk material. In contrast, ablation above 10 J cm⁻² results in the formation of polydisperse, bimodal aerosols, which are distributed around d_p1 ≈ 20 nm (w_p1 ≈ 50 nm) and d_p2 ≈ 1 μm (w_p2 ≈ 5 µm), respectively, and whose total Cu/Zn ratio slightly deviates from the bulk composition. In order to examine the influence of pulse duration on particle size distribution and aerosol composition, comparative measurements by means of near-IR nanosecond ablation were also performed. The data show that nanosecond ablation generally leads to an intensified formation of particles in the micrometer range. Moreover, the composition of these aerosols strongly departs from the stoichiometry of the bulk. Aspects concerning the formation of particles during ablation as well as implications for the element-selective analysis by inductively coupled plasma spectrometry are discussed.