Optical sensitization for laser-induced breakdown spectroscopy using argon nanobubbles

This paper demonstrates the validity and usefulness of laser-induced breakdown spectroscopy (LIBS) measurements enhanced by argon nanobubbles. The use of argon nanobubbles in the LIBS system revealed a higher sensitivity than that of conventional methods for LIBS solution measurements. To make the nanobubbles, argon gas was pumped into water, forming bubbles less than 100 nm in diameter. The solution of dissolved argon bubbles was used for the following measurements: (1) the hydrogen atomic spectrum (λ = 656 nm) from the water molecules (H₂O) in the solution and (2) the nitrogen atomic spectrum (λ = 399.5 nm) from the air bubbles in the solution. These experimental results demonstrated that the argon nanobubbles have the ability of instantaneous plasma retention during the excitation/relaxation period, which is essential for highly sensitive spectral measurements. The intensity of nitrogen spectra (measurement (2)) obtained from the argon-air nanobubbles in water was much higher than that of the spectra obtained from normal LIBS air measurements.