Radiative cascades

Recently, it has been found, that some of the doubly excited levels, are influenced by radiative cascades within the Li-like system. This is especially important for levels with small auto-ionization rates Aa and hence low population due to dielectronic recombination. The temperature dependence is taken into account by corrections to (8.2) [18]. 

The excited initial state can be produced either directly or by means of radiative cascades and non-radiative transfers. The first is the most probable process, i.e. a filling up by direct inner shell excitation. As a consequence, the R lines are observed only when the hole is created by electron bombardment and not by bremsstrahlung irradiation 12). 

However, a single excitation temperature cannot explain the various observations so that a detailed analysis of the different excitation processes has to be performed for each considered molecule. Black Dalgarno (1977) have analysed the case of the Hydrogen molecule and have shown that radiative pumping followed by UV fluorescence in the Lyman and Werner band systems and subsequent radiative cascades have to be considered as well as collisional excitation by H, H, H, e of the ground vibrational rotational states. Van Dishoeck Black (1982) have analysed the various processes arising for the interstellar Cj molecule and pointed out, that in addition to the mechanisms mentioned above for H, one has to include intercombination transitions between the nearby X ground state and a excited state. 

The equilibrium propulations n j in the ground vibrational state for a molecule submitted to radiation pumping followed by fluorescence and subsequent radiative cascades inside the ground state and collisions are expressed in the following expression ... 

As pointed out by C.H.S.H., pairs of photons emitted in suitable atomic radiative cascades are good candidate for a sensitive test. Consider for instance a (J = 0)->(J = = 0)... 

Fig. 6. Radiative cascade emitting pairs of photons correlated in polarization, that only even isotopes can be used ).

Fig.6.4. A simplified energy-level diagram showing the foil excitation and radiative cascade processes.

The problems associated with radiative cascade in beam-... 

In order to derive the conditions necessary for steady state population inversion in a gas discharge, let the upper level be populated by collisions and radiative cascade from higher excited levels at the total rate atoms m s, as shown schematically in Fig.11.2. The corresponding rate for the lower laser level, S, specifically excludes the cascade contribution from level k to level i since, as we shall see later, this particular mechanism plays a significantly different role from those of the other contributing processes. 

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