Excimer laser

An excimer laser, sometimes more correctly called an exciplex laser, is a form of ultraviolet laser which is commonly used in the production of microelectronic devices, semiconductor based integrated circuits or "chips", eye surgery, and micromachining. Since 1960s excimer lasers are widely used in high-resolution photolithography machines, one of the critical technologies required for microelectronic chip manufacturing. The term excimer is short for 'excited dimer', while exciplex is short for 'excited complex'. Most excimer lasers are of the noble gas halide type, for which the term excimer is, strictly speaking, a misnomer. (Although less commonly used, the proper term for such is an exciplex laser.) Excimer laser was proposed in 1960 by Fritz Houtermans. The excimer laser development started with the observation of a nascent spectral line narrowing at 176 nm reported in 1971 by Nikolai Basov, V. A. Danilychev and Yu. M. Popov, at the Lebedev Physical Institute in Moscow, using liquid xenon dimer (Xe2) excited by an electron beam. Spurred by this report, H.A. Koehler et al. presented a better substantiation of stimulated emission in 1972, using high pressure xenon gas. Definitive evidence of a xenon excimer laser action at 173 nm using a high pressure gas at 12 atmospheres, also pumped by an electron beam, was first presented in March 1973, by Mani Lal Bhaumik of Northrop Corporation, Los Angeles. Strong stimulated emission was observed as the laser's spectral line narrowed from a continuum of 15 nm to just 0.25 nm, and the intensity increased a thousand-fold. The laser's estimated output of 1 joule was high enough to evaporate part of the mirror coatings, which imprinted its mode pattern. This presentation established the credible potential of developing high power lasers at short wavelengths. A later improvement was the use of noble gas halides (originally Xe Br) developed by many groups in 1975.