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a device that transfers light of various frequencies into an extremely intense, small, and nearly nondivergent beam of monochromatic radiation in the visible or invisible spectrum, with all the waves in phase; capable of mobilizing immense heat and power when focused at close range, lasers act on tissues by photocoagulation and photodisruption and are used in surgery, in diagnosis, and in physiological studies.
argon laser a laser with ionized argon as the active medium and with a beam in the blue and green visible light spectrum; used for photocoagulation.
carbon-dioxide laser a laser with carbon dioxide gas as the active medium and that produces infrared radiation at 10,600 nm; used to excise and incise tissue and to vaporize.
excimer laser (excited dimer) a laser with rare gas halides as the active medium, used in ophthalmological procedures and angioplasty. The beam is in the ultraviolet spectrum and penetrates tissues only a small distance; it breaks chemical bonds instead of generating heat to destroy tissue.
holmium:YAG laser a laser whose active medium is a crystal of yttrium, aluminum, and garnet doped with holmium ions, and whose beam is in the near infrared spectrum at 2100 nm; used for photocoagulation and photoablation.