FORMATION OF VAPOR CAVITY UNDER HYDROACOUSTIC TREATMENT OF BIOLOGICAL TISSUE IN LIQUID BY MICROSECOND PULSES OF Er,Yb:Glass-LASER RADIATION
Annotation
Results of a study of dynamics of the shape and size of vapor-gas cavities excited by laser pulses on ytterbium-erbium glass with a fiber output at a wavelength of 1.54 µm in the free volume of liquid (water), as well as near boundary of a solid (quartz) and elastic object (lens of the eye) are presented. The influence of temporal structure of the pulses of total duration in microseconds on appearance and process of formation of the vapor cavity in liquid is investigated. It is found that at a fixed pulse energy in the free volume of the liquid, an increase in the power of the "leading" peak in the laser pulse leads to a decrease in the threshold of formation and an increase in the maximum volume of the cavity. In the free volume of the liquid with a total laser pulse duration of 3–3.5 µs and energy of the order of E = 100 mJ, the maximum volume of the vapor-gas cavity reaches 7 mm3 at the laser radiation intensity of the order of 108 W/cm2 at the output end of the optical fiber at the time of the action of the leading peak. The maximum volume of the vapor-gas cavity is achieved within 165 ± 5 µs from the beginning of the laser pulse, and the cavity collapse occurs after 300 ± 10 µs. Reducing the intensity while maintaining the total energy of the pulse leads to a slowdown in the growth of the vapor-gas cavity and a decrease in its maximum volume. Near the boundary of the solid, the vapor-gas cavity is deformed and acquires a smooth hemispherical shape, its volume decreases, and the lifetime increases to 350 ± 10 µs. Near the border of the elastic body, the vapor-gas cavity is also deformed, acquires a hemispherical shape, but in the collapse phase near the lens, micro bubbles of 40–120 µm size are formed on the surface of the cavity. Near the cataract lens, the time to reach the maximum volume of the cavity and the time of its life are reduced compared to the formation near the boundary of the solid and in the free volume of water, and the lens of the eye is destroyed.
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