Excimer lamps incoherent radiation

The most important difference between excimer and standard UV lamps is that the former are incoherent radiation sources and can therefore be used for large area applications. Different wavelengths can be produced by choosing different gas fills in the gap between the quartz tubes. 

Tab. 3.3 Spectral domains of electromagnetic radiation (VUV, UV, VIS and IR), energy conversions, principle emission lines of mercury arc lamps, and of some novel incoherent excimer lamps...

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 . ... 

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. 

Excimer lamps were selected to study the low fluence irradiation region, where linear (no ablation) photochemistry is taking place. This is the fluence range (e.g., insert in Fig. 47 of the previous chapter), where a linear relation between reaction products and laser fluence is observed. This may correspond to the range of linear photochemistry, i.e., below the threshold of ablation (see, e.g., Figs. 25 and 26), or the so-called Arrhenius tail. The excimer lamps emit at the same wavelengths as the excimer lasers, but with incoherent radiation, and in quasi-CW mode. The peak photon fluxes of the lamps are low compared to the excimer laser, suggesting that multiphoton processes are not important. Thin films of the triazene polymer on quartz substrates were irradiated with the excimer lamps under different conditions, i.e., in Ar, air, and 02. 

The incoherent excimer radiation from a dielectric barrier discharge (silent discharge), operating in pure xenon, gas mixtures of krypton/chlorine, and xenon/chlorine, provides intense narrow-band radiation. More details about the excimer UV sources can be found in the literature [236, 237]. As irradiation sources a XeCl (308 nm), a KrCl (222 nm), and a Xe2 (172 nm) excimer lamp were selected. Excimer lamps based on fluorine-containing excimers are difficult to operate, due to etching of the quartz housing by the F2. 

Fig. 4.15 Photograph of an incoherent excimer flow-through lamp (Pel = 150 W) with coaxial radiation geometry (configurations see Figs. 4-13 and 4-14).

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