Laser therapy is a relatively new therapeutic modality. For some time, high power lasers have been used in medical treatments such as surgery and coagulation. Some beneficial effects were noticed near the treated areas which led to research into the benefits of lower powered lasers. Laser therapy at low powers has been investigated for many years and recently authorities such as the FDA have recognized the efficacy of therapeutic lasers in some applications after many years of rigorous research.

Laser radiation directed at tissue can either be reflected off the surface of the tissue or penetrate into the tissue. Whether the light reflected or penetrates depends on several factors such as wavelength, tissue surface condition, and the beam angle of incidence.

Once the laser light has penetrated the tissue, the light is internally scattered by three optical effects: divergence, reduce the depth of penetration in the tissue.

This process of photochemical stimulation is considered to be the prime interaction that provides the therapeutic benefit, although some photo-thermal interactions are considered beneficial as well.

References:
“Clinical Laser Therapy”, Jimmie Kert, M.D. & Lisbeth Rose, M.D. Scandinavian Medical Laser Therapy, ISBN 87-983204-1-6

“Electrotherapy Explained”, John Low & Ann Reed, Butterworth-Heinemen, ISBN 0-7506-4149-