Generation of Monochromatic UV Radiation

Excimer and nitrogen lasers are sources of pulsed monochromatic UV radiation with a variety of interesting wavelengths and high-output peak powers. 

Spectral outputs of some typical metal halide lamps compared to that of the standard mercury lamp mercury barrier discharge lamp (a) mercury barrier discharge lamp, (b) iron additive lamp, and (c) gallium additive lamp. (Courtesy of American Ultraviolet Company.) 

However, they cannot compete with mercury arc lamps in large-area, fast-cure applications because of their low pulse repetition rates.  

Excimer lamps, a relatively recent new development, represent a new class of monochromatic UV sources. Excimers (excited dimers, trimers) are weakly bound excited states of molecules that do not possess a stable molecular state.  

The term stands for an electronically activated molecule in the gas phase consisting of two atoms. The formation process is the same as in lasers  

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Monochromatic UV radiation is emitted by excimer lamps, in which microwave discharge5 or a radio-frequency-driven silent discharge6 generates excimer-excited states of noble gas halide molecules, which decay by the emission of monochromatic UV radiation. In the ground state, the excimer molecules decay into atoms. Therefore, no self-absorption of the UV radiation can occur. All photons are coupled out of the discharge.4... 

It is possible in theory to generate an action spectrum which takes into account the effect of incremental monochromatic radiation in excess of the spectral irradiance of a source spectrum. Narrow-band, near-monochromatic radiation might be superimposed over the polychromatic spectrum from a xenon source to obtain radiation spectrally enhanced in any selected waveband. Using a series of interference filters, a series of cut-on filters, and two filtered xenon sources, it should be possible to generate an action spectrum for polymer degradation under spectrally-altered, UV-enhanced (or even visible-enhanced) source spectra. The effective radiation and dose rate in such an experiment can be written as follows ... 

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