External light

The simplest and of course the most inexpensive external light source is the sun. This source, however, is not always as dependable and reproducible as the photochemist would like. Alternatively, a sun lamp, whose... 

One disadvantage to using external light sources is that for irradiations using 2537-A light, a Pyrex reaction vessel cannot be used since Pyrex absorbs strongly at wavelengths less than 3000 A. Therefore more expensive quartz vessels must be used. 

Compared to photoluminescence processes, no external light source is required, which offers some advantages such as the absence of scattering or background photoluminescence signals, the absence of problems related to instability of the external source, reduction of interferences due to a nonselective excitation process, and simple instrumentation. 

CL is the emission of light by molecules that are excited by participation in a highly exergonic reaction, usually an oxidation. It can also be defined as the fluorescence of the electronically excited product of a chemical reaction however, unlike fluorescence, no external light source is used. 

D. Gonze, M. Roussel, and A. Goldbeter, A model for the enhancement of fitness in cyanobacteria based on resonance of a circadian oscillator with the external light-dark cycle. J. Theor. Biol. 214, 577-597 (2002). 

The next section, which is the most extensive, deals with the various kinds of spectroscopic experiments which have been done or can be done with lasers as external light sources, where external means that the probe under investigation is placed outside the laser resonator. Together with a brief description of the experiments and a summary of the results, there is a discussion of the main qualities of the laser which made these special investigations possible. 

The last two chapters discussed spectroscopic studies which used coincidences between laser lines and transitions in other atoms or molecules. These investigations have been performed either with lasers as external light sources, or inside the laser cavity. In the latter case coupling phenomena occur between the absorbing species and the laser emission, one example of which is the saturation effect employed in Lamb dip spectroscopy and laser frequency stabilization. This chapter will deal with spectroscopic investigations of the laser medium itself and some perceptions one may obtain from it. 

Figure S. (a) A dilute solution of a dye D in equilibrium with a black body at temperature Ti but with no external radiation (b) same system as in (a) but with an external light beam irradiating the dye solution such that D is being excited to...

PUs are also widely used as coating materials sold as finished polymers, two-part systems, and prepolymer systems. Water-based PU systems are now available allowing easy home use. Aromatic diisocyanate-derived coatings generally offer poor external light stability while aliphatic-derived systems offer good light stability. 

Menaker We can t forget that organisms are exquisitely tuned to their particular environments. A fly does not have the same environment as a rat, even when they are both out in the real world. Even hamsters which live in the desert haven t got the same light environment as voles or rats. The response to the external light conditions will be finely tuned. This will require a lot of subtlety which we probably don t see much of. 

Figure 1.2 shows the basic instrumentation necessary for each technique. At this stage, we shall define the component where the atoms are produced and viewed as the atom cell. Much of what follows will explain what we mean by this term. In atomic emission spectroscopy, the atoms are excited in the atom cell also, but for atomic absorption and atomic fluorescence spectroscopy, an external light source is used to excite the ground-state atoms. In atomic absorption spectroscopy, the source is viewed directly and the attenuation of radiation measured. In atomic fluorescence spectroscopy, the source is not viewed directly, but the re-emittance of radiation is measured. 

In contrast to weak-held (perturbative) quantum control schemes where the population of the initial state is approximately constant during the interaction with the external light held, the strong-held (nonperturbative) regime is characterized by efficient population transfer. Adiabatic strong-held techniques such as rapid... 

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