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10 January 1996 Acoustic wave monitoring during laser ablation of tissue
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The homogeneous and inhomogeneous model media, human aorta tissue were investigated under irradiation of Q-switched Nd-YAG laser and XeCl excimer laser. Temporal course of acoustic pressure with resolution of 3 - 5 ns, the efficiency of ablation, the distribution of ejected droplets over sizes were studied for laser fluencies 0.1 - 15 J/cm2. Pressure course depends on laser fluence and at high fluencies the tensile phase vanishes completely due to recoil pressure of ejected products. The amplitude of the compression wave is proportional to the laser fluence and may be as high as 80 MPa. The efficiency of ablation rise up considerably with laser fluence rise over the threshold. This is connected with the large droplets ejection and streaming from irradiation surface. Droplets with sizes about 1 mm were detected. The efficiency of ablation both for homogeneously and heterogeneously absorbing media is determined by volume density of laser energy. It is two orders higher for the medium, containing absorbing particles rather than for homogeneously absorbing medium. Detection of acoustic wave with high temporal resolution possesses to investigate the laser ablation process in detail. No cold photomechanical damage spallation by the powerful rarefaction wave formed upon the reflection of the laser-induced compression wave at the biotissue-air interface is observed in the course of laser ablation. The higher ablation efficiency for heterogeneously absorbing medium is determined by local overheating of microareas with increased absorption.
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Alexander A. Karabutov, Natalia B. Podymova, and Vladilen S. Letokhov "Acoustic wave monitoring during laser ablation of tissue", Proc. SPIE 2624, Laser-Tissue Interaction and Tissue Optics, (10 January 1996);

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