Hard tissue ablation with sub-μs CO2 laser pulses with the use of an air-water spray

Using short 300 ns pulses of a Q-switch CO2 laser at the wavelength of maximal hard tissue absorption (9.6 mum) we achieve charring-free ablation of bone tissue. An air-water spray prevents tissue parching and helps to avoid excessive rest-heat accumulation. The observed thermally altered layer at the cut surface in a cortical bone is of only 2-6 mum thickness. A long enough irradiation results in a progressively narrowing to the bottom wedge-shaped cut profile and in a drop of the ablation rate as compared to its initial value. The main reason for this is most likely an enhancement of a heat dispersion and growing light absorption by ablation products. An enlargement of the cut width helps to avoid these negative phenomena. Using this technique we overcome restriction on the cut depth and reduce noticeably the cut time. With 66 W of average power from the Q-switch CO2 laser we need 1/2 min to produce a 6-mm deep and 10-mm long in vitro incision in a hard cortical bone (young bull femur). That time increases to 2 min for 10-mm depth.