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STUDY OF HYDRODYNAMIC PROCESSES IN LIQUIDS UNDER THE INFLUENCE OF POWERFUL MICROSECOND YB,ER:GLASS LASER PULSES

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Results of the study of hydrodynamic processes induced in liquid by the Yb,Er:Glass (wavelength of 1,54 μm) laser radiation pulses of microsecond duration with an energy of 100±5 mJ are presented. The investigations carried out using three methods — acoustic signal detection, optical probing, and high-speed video recording – allow for objective and comprehensive picture of excited processes. The correlation between data obtained using these methods are established. The analysis of images and oscillograms demonstrates that the laser pulses, delivered in a bulk of saline (0,9 % sodium chloride aqueous solution) via quartz-quartz optical fiber with a core diameter of 470 μm, induce thermoelastic waves and the formation of steam-gas cavity (bubble). Dynamics of optical properties of the liquid under exposure to Yb,Er:Glass laser pulse appears to be related mostly to the bubble formation. It is shown that the build-up stage of the steamgas cavity occurs at 5—10 s after the beginning of adiabatic laser exposure with the energy of about 100 mJ. The cavity reaches the maximum size (up to 3 mm in diameter) at 140 s (on average) relative to laser pulse rising edge. After that, it collapses to the critical size of 0.5 mm at about 120 s and detaches from the fiber end surface. The presented data on the steam-gas cavity size dynamics may be useful when optimizing the temporal and energy parameters of laser radiation for laser processing of submerged objects, including effective and safe treatment of biological objects.

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