Abstract

IR lasers (2.94 and 10.6 μm) are excellent sources for precise cutting with minimal thermal damage in microlaser surgery due to their strong absorption in water. We explain laser cutting of tissue and its substitute gelatin and agar by a combined action of evaporation, ejection of liquid, and elastic deformation of the region of laser impact. Using high-speed photography we studied this deformation caused by the pressure induced by the recoil of evaporated target material. We found a correlation between temporally well-separated spikes of a 250-μs long ER laser pulse and the diameter of the crater which varies along the crater axis so that zones of big and small diameters alternate. When drilling with the smoothly shaped CO₂ pulse no diameter variation was detected. A more dramatic dynamic deformation was measured by drilling holes in a target containing several layers of different elasticity. The diameter of the hole within the most elastic layer is up to four times larger than the focal spot diameter of 260 μm. This result is in good agreement with the more extended damage zone of the highly elastic muscle cells compared with the surrounding rigid connective tissue that we obtain by cutting mouse skin with a laser.

© 1988 Optical Society of America