Influence of Hydrodynamic Processes Generated by 1.94-μm Pulsed Laser Radiation on Daphnia magna Crustaceans

Abstract: The hydrodynamic processes occurring in water under the action of pulsed laser radiation with a power of 20 W, wavelength of 1.94 μm, and a pulse duration of 100 ns were investigated. Such radiation leads the excitation of jet flows in water, as well as microbubbles and broadband acoustic vibrations. It was established that the main energy of these vibrations lies within the range of 10–15 kHz; they are excited according to the thermal cavitation mechanism and the regime corresponds to superintense nucleate boiling. It was shown that laser-induced hydrodynamic processes exert a pronounced biological effect on Daphnia magna crustaceans, leading to their increased fertility for acoustic doses of 35 and 350 J/m². The experimental data and theoretical estimates show that stimulation of the reproductive function in crustaceans is due to the action of laser-induced low-intensity broadband acoustic vibrations and is not associated with temperature effects. The death of crustaceans and appearance of individuals with maldevelopments were observed for the maximum exposure (300 s). It is shown that the negative effects are related only to the effect of high-temperature microjets on Daphnias.