Autofocus system for a surgical CO(2) laser

An autofocusing (AF) system for a surgical CO(2) laser has been constructed. It controls the distance between the focus position of the drilling radiation with respect to the target surface independently of surface indentations or target movements. It thus leads to a precision instrument that controls the crucial parameter that defines the incision depth. Experiments with gelatin and pork skin show that for a given beam power the incision depth is constant within 12%. The AF system adjusts to distance variations over a 10-mm range, where without autofocusing the drilling depth would drop by 75%. The optical setup is implemented in a handpiece that is attached to the end of a surgical mirror arm. A frequency doubled Nd:YAG laser beam provides the pilot beam for the distance measurement. The distance signal arises from a photometric equilibrium method in combination with a spot wobbling technique.