In this work the process of optical breakdown under laser irradiation by nanosecond pulses with an energy of 650 mJ of aqueous solutions of Ni nanoparticles is investigated. A monotonic change in the number of breakdowns, the average distance between closest breakdowns, the average plasma size of an individual breakdown, the luminosity of a plasma flash, the intensity of acoustic signals, and the rate of formation of dissociation products - O2, H2, OH•, and H2O2 with an increase in the irradiation time was established. With an increase in the concentration of nanoparticles, the measured values change non-monotonically. The maximum luminosity of a plasma flash is observed at a nanoparticle concentration of 109 NP/ml and 1010 NP/ml and reaches 350 cd/m2. The maximum pressure at the shock front is 1.5–2 MPa at a nanoparticle concentration of 1010 NP/ml. The maximum rates of generation of O2, H2, OH• and H2O2 are observed at concentrations of 109 NP/ml and 1010 NP/ml. Correlation analysis of the studied physicochemical phenomena shows that the formation of molecular gases is associated with acoustic processes, and the formation of radical products and hydrogen peroxide correlates with the physicochemical properties of plasma.

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