Spectral Characteristics Of Laser Ablation Threshold Of Soft Biological Tissue

One of the most key problems in laser ablation is that of mastering the relativity of ablation threshold and wavelength, maximizing ablation rate, while simultaneously minimizing heat damage. Irradiation parameters have great influence on tissue ablation characteristics, especially on ablation threshold. In this dissertation, we present the results of a study of tissue ablation characteristics as a function of wavelength by combining numerical analysis and tissue model experiment.At first, a short introduction to the history and actuality of the study of laser ablation in bio-tissue was reviewed briefly, and related opinion was given. Then the purpose to our study was also presented.Secondly, the basic concept related to bio-tissue ablation was outlined. The light distribution, heat conduction and thermal effect during bio-tissue ablation were also expatiated. We obtained the laser heat source term expression and deduced the bio-tissue heat transfer equation, the solution conditions related were also summarized.Thirdly, distributions of light and heat source for three different wavelengths were obtained by numerical simulation. The influence of phase transition on temperature distribution was discussed. Furthermore, the bio-tissue heat transfer equation was solved numerically by Finite Element Method (FEM), the temperature of space distribution and time behavior at different wavelength was shown clearly.Finally, pulse laser ablation of vitro porcine skin was studied with superpulse CO₂ laser, pulse Er:YAG laser and pulse Ho:YAG laser. The ablation effect for different laser sources was compared and analysed, the range of ablation threshold related was being found. The ablation efficiency was also discussed.