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L.A.S.E.R. Light Amplification by Stimulated Emission of Radiation. Click on the green arrow to return to the previous page
Lasers work by creating a population inversion of electrons within metastable energy levels in a lasing medium, which can be gas,liquid or solid. These metastable states are induced through the introduction of special impurity atoms which allow many electrons to be raised to higher energy levels. These electrons then decay to the lowest ground state energy level emitting a pulse of coherent light. These pulses are then amplified within the lasing medium by multiple internal reflections until they reach a threshold intensity and are realeased as a high intensity beam of a specific wavelength determined by the characteristics of the lasing medium.
Lasers find countless applications in industrial processing, the most obvious example being the cutting and drilling of complex shapes under computer control. A different application I investigated was to ascertain the efficacy of using laser ablation to quickly and effectively removed cross-linked epoxy resin contamination from metal molds used repeatedly by aerospace manufactuers to fabricate aircraft fuselarges.Cured epoxy resin is resistance to chemical attack and the coventional cleaning method then used was mechanical abrasion, which was both time consuming and damaging. Laser candidates were those operating in the infra-red region of the electromagnetic spectrum, such as carbon dioxide lasers (which would burn off the resin if defocuused) or lasers of shorter wavelength, notably Nd-YAG solid state lasers. (Nd-YAG is Neodynium doped yttrium aluminium garnate crystal which will lase at approximately 1 micron wavelength compared to CO2 gas laser which operates at a wavelength of just over 10 microns wavelength). Nd-YAG lasers are frequently used in art conservation to clean stonework. I found the latter laser to be cost effective and efficient for the aerospace application but the process of removal was largely by virtue of the mechanical shockwave resulting from the laser generated plasma at a metal surface rather than due to any absorption of the laser energy by the resin.Greater absorption occured at the metal-oxide layer interface which effectively destroyed the adhesion of the resin to the metal mold.The cleanliness of the resulting metal was determined using Auger and X-Ray Photoelectron emission spectroscopy.