Synthesis and optical characteristics of silver nanoparticles produced by laser ablation of metal in liquid

The process of silver ablation in water by high-power laser pulses (λ = 1064 nm, τ = 20 ns) in the power density range from 2.6 ⋅ 108 to 5.5 ⋅ 108 W/cm2 has been investigated. The dependences of the ablation efficiency and the size distribution of silver nanoparticles on the power density of laser radiation and on the duration of synthesis have been determined. It was found that the resulting nanoparticles have a multimodal size distribution, in which three fractions with average sizes of 5; 50 and more than 100 nm can be distinguished. Particles with a diameter of more than 100 nm are formed as a result of the removal of the liquid-droplet phase directly from the target surface due to the hydrodynamic mechanism, particles 5 and 50 nm in size are formed due to condensation at different stages of cooling of the vapor-plasma formation. The proportion of these fractions in the silver sol is determined by the effective density of the laser power on the target surface. It is shown that pulsed laser irradiation of a sol of silver nanoparticles after the completion of the synthesis process makes it possible to significantly narrow the particle size distribution and increase the stability of the resulting suspension. It was found that the synthesised silver nanoparticles deposited on a silicon substrate can effectively enhance the Raman signal of human serum albumin.