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10 January 1996 Starting mechanisms of bubble formation induced by Ho:Tm:YAG laser in water
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The starting mechanisms of laser induced bubble formation at the submerged fiber tip was investigated by pressure measurements and fast flash light videography. The radiation of a free running or Q-switched Ho:Tm:YAG-laser operating at a wavelength of (lambda) equals 2.1 micrometers was delivered via a fiber into a water filled cuvette. The spatial intensity distribution at the distal end of the fiber was investigated with a thermal image method. It was shown that the beam profile exhibits hot spots which result in an inhomogeneous temperature distribution of the water volume underneath the fiber tip. It was found that at high laser intensities (3 MW/cm2) micro bubbles can appear already at the very beginning of the laser pulse at average water temperatures below the boiling temperature. Corresponding to each sub-ablative laser spike a bipolar thermo-elastic pressure signal was recorded. We came to the opinion that the lowering of pressure by the negative component of the bipolar pressure transients leads to initiation of bubbles by cavitation at high laser intensities. When the laser intensity was reduced from 1 to 0.5 MW/cm2 a fast increase of the bubble formation temperature was found. At laser intensities less than 0.5 MW/cm2 bubble formation takes place at temperatures near the critical temperature of water.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Flurin Koenz, Martin Frenz, Hans Surya Pratisto, Heinz P. Weber, Alexander S. Silenok, and Vitali I. Konov "Starting mechanisms of bubble formation induced by Ho:Tm:YAG laser in water", Proc. SPIE 2624, Laser-Tissue Interaction and Tissue Optics, (10 January 1996);

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