Before we describe the specific dangers of laser radiation on different human organs, it is useful to present the various effects it can have on organic tissues. One can easily understand that laser radiation, while meeting an obstacle to its free space propagation, provokes some physical effects depending on its power and on the surface on which it is focused.
Thermal effects occur when laser radiation is absorbed by the obstacle (skin). They induce tissue reaction, related to the organism temperature elevation and to the duration of the heating process. Depending on the temperature elevation, different reactions can occur :
Hyperthermia : The temperature rises of only a few degrees. A 41°C temperature during a few tens of minutes can induce cellular death.
Coagulation : It corresponds to an irreversible necrosis without immediate tissular destruction. During this process, the tissue temperature can reach temperatures between 50°C and 100°C during about 1s. This induces dessication, whitening and retraction of tissues due to protein and collagen denaturation. Tissues will afterwards be eliminated (detersion processes) and the wound will scar.
Ablation : it corresponds to matter loss. This process occurs at temperatures higher than 100°C. In these conditions, the cell constituting elements evaporate within a relatively brief time. At the borders of the ablated area, one observes a necrosis coagulated area, as the temperature decreases continuously from the injured to the healthy tissues.
Hazard related to the use of pressurized gas bottles.
Mechanical effects : They are caused by the creation of a plasma, by an explosive vaporisation, or by a cavitation phenomenon. These effects are mainly related to the expansion of a chock wave (created consequently to thermal effects), which in turns has destructive effects. Indeed, when ejecting matter from the substrate, the latter moves backward. This movement is due to the energy/momentum conservation, and to the fact that a part of the electromagnetic energy is converted into kinetic energy.
These effect can be seen from two opposite perspectives. When they accidentally happened, consequently to a lack of precautions, they are harmful. However, when used appropriately, they can have therapeutic effects. The chock wave can for example be used in ophthalmology, or in the industry.