This stands for Light Amplification by Stimulated Emission of Radiation. The light produced by a laser is of a single wavelength and all the waves are in phase with each other, allowing a very high level of energy to be projected as a parallel beam or focused on to a small spot.

Various gases, liquids and solids will emit light when they are suitably stimulated. A gassed laser is pumped by the ionising effect of a high-voltage current. This is the same process as that used in a fluorescent tube. Each type of laser has a different effect on biological tissues and this is related to the wavelength of the light produced. The wavelength determines the degree of energy absorption by different tissues and, because of this, different lasers are needed for different tasks. The two main uses of laser in surgery are the endoscopic (see ENDOSCOPE) photocoagulation of bleeding vessels, and the incision of tissue. The argon laser produces light in the visible green wavelength which is selectively absorbed by HAEMOGLOBIN. It heats and coagulates (see COAGULATION) tissues so can be used to seal bleeding blood vessels and to selectively destroy pigmented lesions. The carbon-dioxide laser is the standard laser for cutting tissue: the infra-red beam it produces is strongly absorbed by water and so vaporises cells. Thus, by moving a finely focused beam across the tissue, it is possible to make an incision.

Lasers have important applications in OPHTHALMOLOGY for the treatment of such disorders as detachment of the retina and the diabetic complications of proliferative retinopathy, and of the cornea (see EYE, DISORDERS OF). The destruction of abnormal cells in the CERVIX UTERI – a sign of pre-malignancy – is done using lasers. The beams may also be used to remove scar tissue resulting from infection of the FALLOPIAN TUBES, thus unblocking the tubes and improving the chances of CONCEPTION. Lasers also have several important applications in DERMATOLOGY. They are used in the treatment of pigmented lesions such as LENTIGO; in the obliteration of port-wine stains; in the removal of small, benign tumours such as verrucas; and finally in the removal of tattoos.

Low-intensity laser beams promote tissue healing and reduce inflammation, pain and swelling. Their effect is achieved by stimulating blood and lymph flow and by cutting the production of PROSTAGLANDINS, which provoke inflammation and pain. The beams are used to treat ligament sprains, muscle tears and inflamed joints and tendons.

The three great advantages of lasers are their potency, their speed of action, and their ability to focus on an extremely small area. For these reasons they are widely used, and have allowed great advances to be made in microsurgery, and particularly in FIBREOPTIC ENDOSCOPY.