Dynamics of Submicron Gold Particle Formation during Laser Ablation in Supercritical Carbon Dioxide

The dynamics of submicron gold particle formation during laser ablation in supercritical and liquid CO2 are investigated using time-resolved Mie scattering absorption spectroscopy. It is found that a high density of CO2 of approximately 800 kg/m3, regardless of the phase state, leads to the formation of laser-induced medium fluctuations on time scales of 10 to 1000 μs, during which the defocusing of subsequent laser pulses may occur. Under conditions of the reduced fluid density in the vicinity of the Widom region (P = 8.5 МРa, T = 310 K), it is demonstrated that nanoparticles can leave the interaction zone unhindered as evidenced by the exponential increase in integral absorption. Data from the absorption spectra allow the observation of the nanoparticle formation dynamics with an average diameter of approximately 160 nm and a log-normal size distribution, the width of which is determined by the thermodynamic conditions of CO2.