STUDY OF ACOUSTIC SIGNAL DURING LASER HYDROACOUSTIC PROCESSING OF BIOLOGICAL TISSUE BY MICROSECOND PULSES OF YTTERBIUM-ERBIUM GLASS LASER RADIATION

Subject of Research.The paper describes the research results of an acoustic signal recorded by a hydrophone while effect on a liquid by microsecond pulses of laser radiation with a wavelength of 1.54 μm and different time substructure. We discuss the influence of energy and time substructure of the laser pulse on the magnitude of generated pressure drops in the liquid and removal efficiency of cataract eye lens tissues. Method. Microsecond pulses of ytterbium-erbium glass laser radiation with different peak power of the "leading" spike and equivalent energy were delivered to the volume of distilled water through an optical fiber. The acoustic signal was registered with "NP 10-1" needle hydrophone (Dapco Inc., USA). An in vitro hydroacoustic treatment of cataract human eye lens was performed. Main Results. We obtained the dependences of the amplitude of the first (thermo-optical) and the second (associated with "collapse-rebound" process of a steam-gas cavity) components of the acoustic signal on the pulse energy for laser pulses with different time substructures. It was established that with an increase in the peak power of the "leading" spike of microsecond pulse, the threshold for the appearance of the second component decreases, and the maximum amplitude of both components increases. The angular distributions of the amplitude of acoustic signal components were obtained. It was found that the first component has a pronounced maximum amplitude in a direction perpendicular to the optical axis of the fiber, whereas the angular distribution of the second component is more uniform. In the in vitro experiment, it was shown that an increase in the peak power of the "leading" spike results in a significant increase in the removed volume and removal efficiency of the human cataract eye lens. Practical Relevance. The obtained results can be used to optimize the parameters of laser radiation for processing of tissue surrounded by a liquid, for example, during laser cataract extraction.

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