Development of Incoherent Excimer Lamps

In contrast to coherent radiation emitted by laser sources, incoherent or non-co-herent radiation is characterized by elementary electromagnetic waves that do not have any phase relation in space and time. The production of incoherent excimer radiation in the UV or VUV region of the electromagnetic spectrum is made pos- 

The electrical discharge is operated by an alternating high voltage with amplitudes of several kV and in the kHz to MHz frequency range. Commercially available excimer lamps (Xe2, KrCl and XeCl ) are usually powered by plasmagen-erators with an electric power of 20 W, 150 W or 1.5 kW. Electronic ballasts of higher power are under active development. 

The geometric variability of silent discharge configurations leads to an enormous flexibility in excimer lamp design (Fig. 4-12). Different tubular radiation 

For photochemical reactions, usually the lamp configuration with an annular discharge gap is preferred. Consequently, a typical experimental setup is demonstrated schematically by Fig. 4-13 (Oppenlander, 1997 a, Oppenlander et al., 1996, 1995, Oppenlander and Baum, 1994, Braun et al., 1993). It consists of a cylindri- 

Inner Electrode Metal Wire or Static Mixer 

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In the H2O-VUV AOP no additional auxiliary oxidants must be used to produce sufficient amounts of OH radicals. The technical development of incoherent exci-mer VUV and UV sources of electromagnetic radiation (see Chapter 4.3) led to a renaissance of research related to water photolysis. Hence, the experimental conditions and results of several recent investigations that deal with the applications of VUV and UV incoherent excimer lamps in the field of AOP research (mainly in aqueous media) are briefly summarized in Tab. 7-2. 

Recently, several interesting applications of actinometers were published. For example, the fluence rate distribution Eq in mW cm at X of 253.7 nm in UV reactors can be determined by the iodide/iodate system (Stefan et al., 2001, Rahn, 1997), this being important for UV disinfection development. In connection with the development of novel incoherent excimer UV lamps several actinometric procedures have been applied to establish their radiant power efficiency, e.g. using 3,4-dimethoxynitrobenzene at X of 308 nm (Zhang et al., 1999), uridine at 222 nm (Zhang et al, 1997), hydrogen bromide (Pfeifer Roland et al., 1998), oxygen (Las-zlo et al, 1998) and methanol (Heit et al, 1998) at X of 172 nm. 

In addition, a novel generation of lamps with promising features for photochemical applications has been developed to industrial maturity over the last decade, the so-called incoherent excimer radiation sources (Eliasson et al., 1988). Note that these lamps are not laser sources. In contrast to well-known excimer lasers, excimer lamps are operated under different physical conditions and they emit incoherent electromagnetic radiation. Whereas pulsed laser radiation can reach very high irradiances, E up to 100 MW m , the irradiance E of excimer lamps is only in the range of 1000 W m . ... 

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