Excimers are temporary combinations of two excited atoms that emit fluorescent light when they dissociate. Excimer lasers use reactive and inert gases to create these dimers, emitting ultraviolet light that can reshape or eliminate superficial tissue. Excimer lasers have applications in eye surgery, dermatology, and microchip manufacturing.
An excimer is a transient combination of two atoms, called an excited dimer, in which at least one atom exists in an electronically excited state. Under normal conditions, atoms contain two electrons per energy level surrounding their protons, with the electrons spinning in opposite directions. When the atom absorbs energy from light, an electron can move to a higher energy orbit, leaving an unpaired electron. The atom combines with another atom to form a dimer only under these excited circumstances, and when the dimer releases its energy and the electron returns to its ground state, the dimer dissociates, emitting a fluorescent light. An excimer can typically only last a few nanoseconds.
Excimer lasers are ultraviolet lasers used for eye surgery, micromachining, and creating computer chips. With pressure and electricity, the laser creates dimers by passing an electric current through mixtures of reactive gases, such as fluorine or chlorine, and inert gases, such as krypton or argon. Inert gas molecules temporarily bind to reactive gases, forming excited compounds that release energy spontaneously or by stimulation. When the molecules release their energy and dissociate, ultraviolet (UV) laser light is emitted.
Ultraviolet light disrupts the molecular bonds in biological or organic tissues or materials. It has a low degree of penetration and the affected tissue disintegrates in the air instead of burning. For these reasons, excimer lasers are used to reshape or eliminate superficial tissue on the ocular surface. Laser-assisted interstitial keratomylieusis (LASIK) is the application of excimer-derived UV light to the tissue underlying an outer flap of the cornea to adjust the curvature of the cornea. Flattening the corneal shape treats myopia and stiffening the cornea treats farsightedness. In addition, irregular areas of the corneal contour that produce astigmatism can be eliminated.
In addition to eye surgery to treat focusing problems, excimer lasers have other health-related applications. Excimer lasers have been used in angioplasty operations to open blockages in clogged arteries. Dermatologists have used xenon chloride excimers to disintegrate a variety of skin lesions, including vitiligo and psoriasis. Ophthalmologists are able to carefully remove superficial corneal scars using the excimer laser.
Deep ultraviolet light (DUV) lasers using krypton-fluorine or argon-fluorine dimers emit light with wavelengths from 193 to 248 nanometers (7.8 X10-6 to 9.8 X 10-6 inches). From an industrial point of view, manufacturers of microchip devices use these deep excimer lasers for high resolution photolithography. This allowed data to be captured in as little as ten nanometers and allowed for the production of computer chips that were smaller and denser than chips made with older technology. Microchips have gradually decreased in size from 0.5 micrometres (2 X 10 -5 inches) in 1990 to about 43 nanometers (1.7 X 10 -6 inches) in 2010. In addition, excimer lasers have made it possible to cut plastics and polymers with extraordinary precision.
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