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J Biophotonics. 2018 Oct;11(10):e201700373. doi: 10.1002/jbio.201700373. Epub 2018 Jun 28.

Ultrafast dynamics of hard tissue ablation using femtosecond-lasers.

Author information

1
Josef Ressel Center for Material Processing with Ultrashort Pulsed Lasers, Research Center for Microtechnology, Vorarlberg University of Applied Sciences, Dornbirn, Austria.
2
Lasercenter of Munich University of Applied Sciences, Munich, Germany.
3
LIFE-Zentrum, Laser-Forschungslabor, Hospital of University of Munich, Munich, Germany.
4
Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany.
5
Department of Urology, Hospital of University of Munich, Munich, Germany.

Abstract

Several studies on hard tissue laser ablation demonstrated that ultrafast lasers enable precise material removal without thermal side effects. Although the principle ablation mechanisms have been thoroughly investigated, there are still open questions regarding the influence of material properties on transient dynamics. In this investigation, we applied pump-probe microscopy to record ablation dynamics of biomaterials with different tensile strengths (dentin, chicken bone, gallstone and kidney stones) at delay times between 1 picosecond and 10 microseconds. Transient reflectivity changes, pressure and shock wave velocities and elastic constants were determined. The result revealed that absorption and excitation show the typical well-known transient behavior of dielectric materials. We observed for all samples a photomechanical laser ablation process, where ultrafast expansion of the excited volume generates pressure waves leading to fragmentation around the excited region. In addition, we identified tensile-strength-related differences in the size of ablated craters and ejected particles. The elastic constants derived were in agreement with literature values. In conclusion, pressure-wave-assisted material removal seems to be a general mechanism for hard tissue ablation with ultrafast lasers. This photomechanical process increases ablation efficiency and removes heated material, thus ultrafast laser ablation is of interest for clinical application where heating of the tissue must be avoided.

KEYWORDS:

ablation; elastic constants; femtosecond-laser; hard tissue; microscopy; pump-probe; ultrafast laser; ultrashort pulse laser

PMID:
29845754
DOI:
10.1002/jbio.201700373

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