Ablation of Calcified Biological Tissue Using Pulsed Hydrogen Fluoride Laser Radiation

Calcified tissue (primiarly beef shank bone) was ablated in air with an HF laser beam focused to a spot diameter of 150 pm and at several wavelengths in the 2.7-3.0 pm range. Pulse irradiances ranged from 0.2 to 1.0 MW/mm², pulse durations from 350 to 1000 ns, and the pulse repetition rate was 0.5 Hz. Under histologic examination, tissue craters appeared cleanly cut with smooth walls and minimal charring. Fluence thresholds for tissue removal were — 10 mJ/mm², independent of the ablation wavelength. Ablation was observed to occur both with and without the presence of a plasma. The amount of energy required to ablate tissue ranged from 2 to 3 J/mm³, similar to the value observed in noncalcified tissue. Debris ejected from the crater during ablation contained particles of average diameter ~500 nm, expelled from the crater at ~200 m/s. A discussion of the chromophores and mechanisms responsible for the ablation process, as well as a mathematical analysis of the effects of laser beam attenuation by debris particles, is presented. © 1990 IEEE