Thermal Ablation of Mouse Skin Tissue Using Ultra-Short Pulse 1552 nm Laser

Analysis of biological tissue ablation by an ultra-short pulse laser and the corresponding mathematical modeling of ablation are of fundamental importance to the understanding of laser-tissue interaction for advancing surgical application of lasers. The objective of this paper is to analyze the thermal ablated damage zones during irradiation of freshly excised mouse skin tissue samples by a novel approach of using a focused laser beam from an ultra-short pulse laser source. Experiments are performed using Raydiance Desktop Laser having a wavelength of 1552 nm and a pulse width of 1.3 ps. Mouse tissue samples are translated in a direction perpendicular to the laser beam using three-axis automated motion-controlled stages. Scanning of the tissue sample ensures a fresh region of the tissue is irradiated each time. The surface temperature distribution is measured using a thermal imaging camera. It is observed that use of focused beam results in minimal radial heat spread to the surrounding tissue regions. The ablation phenomenon is analytically modeled by the use of two-phase transient heat conduction model. After completion of tissue irradiation experiments, histological studies are performed using frozen sectioning technique to observe morphological changes in tissue samples in response to laser irradiation. The ablation depth measurements obtained using histological studies are compared with the modeling results. A parametric study of various laser parameters such as time-average power, pulse repetition rate, and pulse energy, and as well as irradiation time and scanning velocity is performed to determine the necessary ablation threshold. Analytical modeling results are in very good agreement with experimentally measured ablation depth. The goal of this research is to develop a tool for selection of appropriate laser parameters for precise clean tissue ablation.