Depopulation effect

Let us now consider the situation, discussed in Chapter 3, where the pumping parameter x = rp/7 is sufficiently large to create an anisotropic distribution of angular momenta in the ground state, as described by the 

Due to the fact that the effect of a magnetic field on the ground state angular momenta distribution pa(0, ip) causes changes in the excited state distribution pb(9,(p) (see Figs. 4.9 and 4.10), one may expect to observe the ground state Hanle effect in fluorescence intensity difference I — I or in the degree of polarization V B). Indeed, since we have gj /yK 2  

The superpositional Hanle effect may lead to some, at first glance, unexpected peculiarities. Firstly we wish to draw attention to one interesting fact [17] under conditions where the effect has already developed from the ground state (ujj /jk S 1), but that from the excited state 

Note that the superpositional Hanle signal, reflecting overlapping of effects from both levels, coupled with optical excitation, is sensitive to the signs of the Lande factors gj and gj even with Lorentzian geometry, where p = tt/2 in Fig. 4.2(a), contrary to the linear Hanle effect. This is easily understood, since there is a large difference between the cases 

Let us turn to experimental investigations. The ground state Hanle signal was registered on Na2(.X 1 +), K2pT1E J ) [149, 152] for linearly polarized Q-excitation under conditions close to those given in Fig. 4.9. In particular, the detailed studies [12, 18] clearly demonstrated a narrow 

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The example discussed considers the case of weak light excitation, where the first cycle J" —> J (see Fig. 3.14) does not produce ground state optical polarization via depopulation of the J" level. If this is not so, then the signal is described, accounting for depopulation effects, and naturally assumes a more complex shape [30]. 

The effect of temperature upon the situation in Fig. 5-5 is to modify the Boltzmann distribution. Lowering the temperature depopulates the higher-lying energy levels in favour of the lower. Therefore, susceptibility increases with decreasing temperature. Quantitative studies of the simple (first-order )... 

The very low multiphonon decay rates obtained in Example 6.2 from the Po (Pr +) and p5/2 (Yb +) states are due to the large number of effective phonons that need to be emitted -14 and 38, respectively - and so the high-order perturbation processes. As a consequence, luminescence from these two states is usually observed with a quantum efficiency close to one. On the other hand, from the F3/2 state of Er + ions the energy needed to bridge the short energy gap is almost that corresponding to one effective phonon hence depopulation of this state to the next lower state is fully nonradiative. 

In Chapter 5, we discuss in a simple way static (crystalline field) and dynamic (coordinate configuration model) effects on the optically active centers and how they affect their spectra (the peak position, and the shape and intensity of optical bands). We also introduce nonradiative depopulation mechanisms (multiphonon emission and energy transfer) in order to understand the ability of a particular center to emit light in other words, the competition between the mechanisms of radiative de-excitation and nonradiative de-excitation. 

A whole new area of research has been opened by irradiating the triplet system with microwave power and observing its effect on phosphorescence. A very elegant technique for studying dynamics of populating and depopulating the phosphorescent state has been introduced by Schmidt As soon as the phosphorescence of... 

Zero field splitting (zfs) values in photoexcited triplets of primary donor bacteriochlorophyll a in photosynthetic bacteria are much lower than those found for vitro BChla triplets. There is a pronounced difference in kinetics of population and depopulation of the triplet sublevels as well. The differences have been attributed to the effect of BChla dimerization and it is now generally accepted that the primary electron donor in photosynthetic bacteria consists of a BChla dimer (special pair)(l- ). 

In a lecture presented to the Faraday Society,332 Norrish commented on why the higher vibrational levels of NO were observed in the nitrosyl halide experiments but not by absorption in NO irradiation experiments. He reasoned that, as the emission of NO from the AZH + state populates the first five vibrational levels of NO almost equally,341 the fast-exchange reaction (4) can quickly eliminate all the vibrational levels above the first. However, in the nitrosyl halide experiments, the NO may be formed preferentially in very high levels, such as v — 10 or 11, almost exclusively. Thus, reaction (4) cannot occur initially, and depopulation must be by reaction (2). Reaction (2) is considerably slower than reaction (4), because of the increased difference in vibrational energy between the reactants and products resulting from an-harmonic effects. 

Fig. 11.12 Plot of the depopulation cross sections of the Rb n( states by ground state Rb nf( ) (ref. 32) ns (O), nd3/2(x), nd ( ) (ref. 57) np ( ) (ref. 26). The cross sections are plotted vs effective quantum number n. For reference the geometric cross section...

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