Rare gas halide excimer lasers

Laboratories and in 1966 the blue helium-cadmium metal vapor ion laser discovered by W. T. Silfvast, G. R. Fowles, and B. D. Hopkins at the University of Utah. The first liquid laser in the form of a fluorescent dye was discovered that same year by R P. Sorokin and J. R. Lankard of the IBM Research Laboratories, leading to the development of broadly tunable lasers. The first of the rare-gas-halide excimer lasers was first observed in xenon fluoride by J. J. Ewing and C. Brau of the Avco-Everett Research Laboratory in 1975. In 1976, J. M. J. Madey and co-workers at Stanford University developed the first fi ee-electron laser amplifier operating at the infi ared carbon dioxide laser wavelength. In 1985 the first soft X-ray laser was successfully demonstrated in a highly ionized selenium plasma by D. Matthews and a large number of co-workers at the Lawrence Livermore National Laboratory. 

ABSTRACT. Selective chemical reactivity has played a long and vital role in the development of laser technology. Some recent examples of selective reactivity as applied to the understanding of rare gas halide excimer lasers and the search for novel chemically driven lasers are discussed. The future of selective chemistry as a component of laser development is projected. 

The recent discovery of the rare gas halide excimer lasers provides a good example of the capability of molecular lasers for high energy output at short wavelengths. Indeed the kinetic similarities of these devices to existing and proposed chemical lasers offer much encouragement for further chemical laser development. 

FIGURE 3 Potential energy diagram of the XeCI excimer. [Reproduced with permission from D. L. Huestis, G. Marowsky, and F. K. Tittel (1984). Triatomic rare-gas-halide excimers, in Excimer Lasers (Ch. K. Rhodes, ed.), Springer-Verlag, Berlin and New York.]... 

Up to now the rare-gas halide excimers, such as KrF, ArF, or XeCl, form the active medium of the most advanced UV excimer lasers. Similar to the nitrogen laser, these rare-gas halide lasers can be pumped by fast transverse discharges, and lasers of this type are the most common commercial excimer lasers (Table 5.5). 

Jain, Excimer Laser Lithography, p. 93, SPIE Press, Bellingham, WA (1990) J. Ewing, Rare gas halide lasers, Phys. Today 31(5), 93 (1978). 

The first lasing of a rare gas-halide (RGH) excimer (XeBr) was reported by Searles and Hart in 1975. Shortly thereafter, lasing from XeF was reported by Brau and Ewing. Both XeBr and XeF lasers were pumped by intense electron beams. Excimers shown in Table I were reported to lase. In addition to electron-beam pumping, researchers have also employed volume-uniform avalanche discharges with X-ray, UV, or corona preionizations, electron-beam controlled discharges, and proton beams successfully to pump a variety of excimer lasers. 

Some of the applications of third- and higher-order frequency conversion are given in Table VII. The th harmonic generation is used to produce radiation at a frequency that is q times the incident frequency. The most commonly used interaction of this type is third-harmonic conversion. It has been used to produce radiation at wavelengths ranging from the infrared to the extreme ultraviolet. Third-harmonic conversion of radiation from high power pulsed lasers such as CO2, Ndiglass, Nd YAG, ruby, and various rare-gas halide and rare-gas excimer lasers has... 

An ideal mechanism of this type is illustrated in Figure 3.37. Given a chemically produced metastable atom or molecule A, suppose that an association reaction A + BC (ABC) can occur to form an electronically excited excimer molecule (ABC). If radiative transitions to a repulsive energy hypersurface account for the major source of decomposition of the excimer, then efficient laser action may be possible, analogous to that of the rare gas halides discussed in Section 3.4.3. 

In the tube of the excimer laser, a rare gas and a halide are mixed. In general, a transverse discharge is used to excite this gas mixture, resulting in a variety of excitation and associated chemical reaction processes. The chain of different coUisional processes is still not completely understood, despite the success of commercial excimer lasers. The main processes occurring in an XeCl excimer laser are those summarized in Table 4.1. 

Figure 4.5 Schematic energy level scheme for exdmer lasers the exdmer potentials and the laser transition are shown on the left and the electron impact generation processes for the excimer molecule are shown on the right. R rare gas atom X halide atom...

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