1. Different effects of medical lasers

Therapeutic applications of lasers exploit a number of effects that can be produced by the action of a light beam on biological tissue. Whatever the effect used, the mechanism of action always begins with a transfer of the energy carried by the light beam to the tissue. Four effects are usually distinguished:

• the photomechanical effect: energy is transported by very brief pulses of light, inducing the creation of a plasma which generates a shock wave that causes mechanical disruption of the tissue structure;

• the photoablative effect: the energy absorbed by the tissue causes a certain number of molecular bonds to break;

• the thermal effect: energy is locally transformed into heat;

• the photochemical effect: light energy is absorbed by an exogenous...