Intense light sources, effect

CD spectra are measured in an instrument ( spectropolarimeter ) that is, in principle, similar to a single-beam spectrophotometer, but using circularly polarized light. However, because CD effects are usually quite small, and observations need to extend into the far-UV, much more intense light sources are required, and the instruments are rather more specialized (Figure 2.19). 

The Weatherometer consists of an enclosure with a high-intensity light source mounted inside a rotating cylindrical rack on which are mounted test specimens. These units are also supplied with xenon-arc lamps, which are closer in wavelength to natural sunlight. The instrument is equipped for temperature and humidity in addition to the energy source and a programmed spray of water. The effects of SO2, ozone, or nitrous oxides can also be studied. 

You can teU from the double index on the elements of [a] such as a. that this is a second-order effect and generally depends on a more intense light source. 

As the fluorescence is directly proportional to the number of photons absorbed by the sample (in the absence of inner-filter/self-shadowing effects of excessive absorption), it is advantageous to employ very high intensity light sources xenon arcs are highly suitable. Additional excitation intensity may be achieved by greater spectral bandwidths employed on the excitation side, although this may... 

Second, it was shown that, if the porphyrin-containing tumor so produced was irradiated with a visible (or red) light source of moderate intensity, the photodynamic effect came into operation, and photonecrosis of the tumor ensued.19 Subsequent studies, particularly by Dougherty and his colleagues,20 demonstrated the clinical promise of the technique. 

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