chemical lasers at very high power levels, fed by streams of gasses, have been developed and have some industrial applications. Excimer lasers Excimer lasers are powered by a chemical reaction involving an excited dimer, or excimer, which is a short-lived dimeric or heterodimeric molecule formed from two species (atoms), at least one of which is in an excited electronic state. They typically produce ultraviolet light, and are used in semiconductor photolithography and in LASIK eye surgery. Commonly used excimer molecules include F2 (fluorine, emitting at 157 nm), and noble gas compounds (ArF [193 nm], KrCl [222 nm], KrF [248 nm], XeCl [308 nm], and XeF [351 nm]). Ion lasers Argon-ion lasers emit light in the range 351–528.7 nm. Depending on the optics and the laser tube a different number of lines is usable but the most commonly used lines are 458 nm, 488 nm and 514.5 nm. Metal-vapor lasers Metal-vapor lasers are gas lasers that typically generate ultraviolet wavelengths. Helium-silver (HeAg) 224 nm, neon-copper (NeCu) 248 nm and helium-cadmium (HeCd) 325 nm are three examples. These lasers have particularly narrow oscillation linewidths of less than 3 GHz (500 femtometers), making them candidates for use in fluorescence suppressed Raman spectroscopy. The Copper vapor laser, with two spectral lines of green (510.6 nm) and yellow (578.2 nm), is the most powerful laser with the highest efficiency in the visible spectrum. Advantages High volume of active material Active material is relatively inexpensive Almost impossible to damage the active material Heat can be removed quickly from the cavity Applications He-Ne laser is mainly used in making holograms. In laser printing He-Ne laser is used as a source for writing on the photosensitive material. He-Ne lasers were used in reading Bar Codes, which are imprinted on products in stores. They have been largely replaced by laser diodes. Nitrogen lasers and excimer laser are used in pulsed dye laser pumping. Ion lasers, mostly argon, are used in CW dye laser pumping. See also Gas dynamic laser Brewster window List of laser types References http://www.google.com/patents/about?id=r2pmAAAAEBAJ&dq=3,149,290 Patent #3,149,290 American inventions