Abstract:
The processes occurring near the fibre end face in medical technologies using fibre lasers with wavelengths of 0.97 and 1.94 $\mu$m have been experimentally studied. Both absorber-coated and pure end-face fibres were used, with the biotissue modelled as a hydrogel. The processes taking place were examined using acoustic methods, from which spectrograms and waveletograms were constructed. It was shown that near the 'blackened' and clean fibre ends, the generation of broadband acoustic impulses occurs under the influence of continuous laser radiation. Acoustic noise for the end with absorbing coating is represented as quasi-continuous, and for the clean end — in the form of time-dispersed tsunamis of oscillations. It is demonstrated that the beginning of these tsunamis lies in the low-frequency region of 2-20 kHz. It is established that when the ‘blackened’ end of the optical fibre is immersed in the biotissue near the end, the modes corresponding to film and intensive bubble boiling by the thermocavitation mechanism alternate. The obtained results can be used to clarify the mechanism of action of laser radiation on biotissue and to improve medical laser technologies.
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