Price: 10.00
There are many UV sources with different properties commercially available on the
market: hydrogen, deuterium or spectral lamps of very weakintensity at the one
side up to high intensity sources like lasers atthe otherside; Sincethe intensity of
the low intensity lamps is most often far too weak for many applications, industrial
arrangements would become too complicated and are only rarely used. Lasers in
the UV or VUV part of the spectrum are mainly excimér lasers or frequency doubled
solid state devices. Lasers do not only cause high investment costs and high costs
for maintenance but also need experienced experts. Because of these reasons
lasers are still research tools mainly. It is a pity, however, that many of the
applications which could be demonstrated by laser techniques in the laboratories
could not be introduced into industrial production. E.g. selective photochemistry that
requires the narrow spectral width of a laser has found only few applications in
industry.
Main light sources of photochemistryare today mercury lamps; Depending on the
mercury vapour pressure these lamps emit different spectra.The atomic line
spectrum (many lines) of the low-pressure mercury lamp (several mbar Hg vapour
pressure) is well known. Up to 30% efficiency is possible in the 254nm resonance
line. The lamp is used for special applications only. The medium pressure mercury
lamp, however, is most widely used. This source can be manufactured rather cost
efficiently. Its broad sprectrum contains also lines at 313nm, 365nm and even
visible lines of considerable intensity. Ozone production of the high energy photons
must be suppressed by special means for some applications. Doped medium
pressure sources shift the emission to wavelengths of the excited added atoms or
molecules in the discharge. The broadest spectrum is emitted by the high pressure
mercury lamp. Pressure broadening of lines at several bars up to hundreds of bars
of pressure causes a broad-band emission of these sources.
According to the existing UV sources photochemists aimed at, developing a
chemistry that fits to the lamps. In particular the initiator should absorb as much
photons of the source as possible to efficiently use the spectrum. UV photons are
still expensive for industrial applications. Therefore a development began to utilise
the strong emission lines of the mercury lamp also at longer wavelengths.
