AGAINST PAIN, REDUCES INFLAMMATION, ACCELERATES LOCAL METABOLISM. The interactions of the High Energy Laser Therapy with the tissue can be divided into four main categories, depending on the type of process, that follow the absorption and essentially depend on the wavelength, power density and timing of the emission modes (e.g. continuous, pulsed and super-pulsed) of the radiation used: I) Photophysical interactions: the laser?s monochromaticity is used to excite the target chromophor (haemoglobin, myoglobin, water, etc.); II) Photochemical interactions: the absorption process is followed by a series of chemical reactions that alter the biological sub-layer; III) Photothermal interactions: due to the conversion of the energy using in heat; IV) Photomechanical interactions: focusing high power impulses on very small volumes allows obtaining real mechanical vibrations.