Research Papers

Plume dynamics and shielding by the ablation plume during Er:YAG laser ablation

[+] Author Affiliations
Kester Nahen, Alfred Vogel

Medical Laser Center Lu¨beck, Peter-Monnik-Weg 4, D-23562?Lu¨beck, Germany

J. Biomed. Opt. 7(2), 165-178 (Apr 01, 2002). doi:10.1117/1.1463047
History: Received July 23, 2001; Revised Nov. 19, 2001; Accepted Nov. 19, 2001; Online April 18, 2002
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Free-running Er:YAG lasers are used for precise tissue ablation in various clinical applications. The ablated material is ejected into the direction perpendicular to the tissue surface. We investigated the influence of shielding by the ablation plume on the energy deposition into an irradiated sample because it influences the ablation dynamics and the amount of material ablated. The investigations were performed using an Er:YAG laser with a pulse duration of 200 μs for the ablation of gelatin with different water contents, skin, and water. Laser flash photography combined with a dark field Schlieren technique was used to visualize gaseous and particulate ablation products, and to measure the distance traveled by the ablating laser beam through the ablation plume at various times after the beginning of the laser pulse. The temporal evolution of the transmission through the ablation plume was probed using a second free running Er:YAG laser beam directed parallel to the sample’s surface. The ablation dynamics was found to consist of a vaporization phase followed by material ejection. The observation of droplet ejection during water ablation provided evidence that a phase explosion is the driving mechanism for material ejection. The laser light transmission was only slightly reduced by the vapor plume, but decreased by 25%–50% when the ejected material passed the probe beam. At radiant exposures ≈10 times above the ablation threshold, the laser energy deposited into the sample amounted to only 61% of the incident energy for gelatin samples with 90% water content and to 86% for skin samples. For free-running Er:YAG laser pulses shielding must therefore be considered in modeling the ablation dynamics and determining the dosage for clinical applications. © 2002 Society of Photo-Optical Instrumentation Engineers.

© 2002 Society of Photo-Optical Instrumentation Engineers

Citation

Kester Nahen and Alfred Vogel
"Plume dynamics and shielding by the ablation plume during Er:YAG laser ablation", J. Biomed. Opt. 7(2), 165-178 (Apr 01, 2002). ; http://dx.doi.org/10.1117/1.1463047


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