[Demonstration of biophysical effects of pulsed laser irradiation with histological tissue sections]

For therapeutic application of laser light it is necessary to minimize defects in the nonirradiated tissue. These defects depend on the primary mechanism of interaction between tissue and laser light. Three experiments were performed to distinguish between mechanical and thermal effects of nano- and microsecond laser pulses in skeletal muscle of the rat. The light, transmission and scanning electron microscopes were In the ns-experiments the mechanical action of a single ns pulse (8 ns) produced a crater. Only zones I and IV developed. With 50 to 100 pulses all zones can be identified. These results show that a single ns pulse suffices to form a tissue crater by mechanical action. A higher number of ns pulses leads to heat accumulation and produces thermal lesions similar to those seen after application of microseconds-pulses.