Hole burning model

Figure 11-8. Proposed hole burning model for the Ei -dopedglass containing OH bonds. Hole is burned when the OH bonds in state 1 are changedfrom A to B site by laser light irradiation. State II has higher energy compared with the state I and relaxes across the barrier into the state I by heating energy.

As evidenced from the above discussion, vibrational line shapes provide information mostly about intermolecular structure. Transient hole burning and more recently echo experiments, on the other hand, can provide information about the dynamics of spectral diffusion. The first echo experiments on the HOD/ D2O system involved two excitation pulses, and the signal was detected either by integrating the intensity [20] or by heterodyning [22]. The experiments were analyzed with the standard model assuming Gaussian frequency fluctuations. The data were consistent with a spectral diffusion TCF that was bi-exponential, involving fast and slow times of about 100 fs and 1 ps, respectively. 

Pairwise EET rates cannot be directly measured in antenna systems. The closest approach to direct determination is offered on the one hand by time resolved picosecond and sub-picosecond absorption and fluorescence measurements and on the other hand by hole burning spectroscopies. Time resolved techniques do not detect transfer between isoenergetic sites. A somewhat more indirect approach to determining pairwise rates is that of analysing excited state lifetime data in terms of a particular antenna and an EET model. 

The sequence of these laser pulses for hole burning and probing may be called bum and probe. It is illustrated by model simulations in Fig. 1 (see pages 197 and 198). Our scheme is an extension of the pioneering work of Kosloff et al. on hole burning in nuclear wavepack-ets [3—9] see also Ref. 10 (supported by Deutsche Forschungsgemein-schaft). 

Many studies concluded that only D3-symmetry is possible and denied C2-symmetry structures. However, the authors failed to explain the temperature and pressure dependence of the absorption spectrum as the substantial evidence for two ground states. On the other hand, only the temperature and the pressure dependence of the absorption spectrum evidenced the two ground states. Thus, no one has proposed any models of explaining comprehensively all the previous experimental observations and theoretical calculations. We found a convincing model of CV involving two ground states from experimental observations favored by tunable-excitation femtosecond spectral hole-burning technique and theoretical calculations. 

We have adopted the excitonic band model not only because it describes conventional absorption spectroscopy (linear spectroscopy), but because it enables an extremely convenient description of nonlinear experiments, such as pump-probe, dynamical hole burning, or photon echoes. In these third-order experiments one has to consider not only transitions from the ground state to the one-excitonic states but also transitions from the one-excitonic to the two-excitonic states (see Fig. 13). These additional transitions reveal the required information to deduce, at least in principle, the complete coupling scheme. 

Fig. 2 A fit of a viscoelastic model of solvation (solid) to transient hole burning data (points). Temperatures top to bottom 160K to 298K...

A treatment for analysing the excitation and fluorescence multiwavelength polarized decay surfaces has been given for the case of a mixture of noninteracting species. An improved model for analysis of fluorescence anisotropy measurements has been presented. Limitations to the use of intense excitation pulses in fluorescence and thermal lens spectrophotometers are discussed in terms of optical saturation. Such artefacts can be eliminated by reference to the fluorescence quantum yield of Rhodamine 6G. A model has been given to describe spectral diffusion in time-resolved hole-burning spectroscopy. ... 

In the extended CM, the JG relaxation is just part of the continuous evolution of the dynamics. The JG relaxation should not be represented by a Cole-Cole or Havriliak-Negami distribution, as customarily assumed in the literature, and considered as an additive contribution to the distribution obtained from the Kohlrausch a-relaxation. Nevertheless, the JG relaxation may be broadly defined to include all the relaxation processes that have transpired with time up until the onset of the Kohlrausch a-relaxation. Within this definition of the JG relaxation, experiments performed to probe it will find that essentially all molecules contribute to the JG relaxation and the motions are dynamically and spatially heterogeneous as found by dielectric hole burning [180,283] and deuteron NMR [284] experiments. This coupling model description of the JG relaxation may help to resolve the different points of view of its nature between Johari [285] and others [180,226,227,280,281,283,284],... 

We expect that our dynamical theory based on the density mauix formalism can be useful in modeling other fundamental and applied problems of nonlinear optics like spectral-hole burning, self-focusing, white light generation, the dynamics of the spectral profiles of amplified stimulated emission etc. The scope is certainly wide for future researh in these areas. 

In the following we will examine transient hole-burning in a multilevel system using a density matrix calculation. It will be shown that with an appropriate extrapolation procedure from the observed hole-width not only optical Tj can be measured but also the transition dipole and intramolecular relaxation constants may be obtained. We will then proceed by using a kinetic model to examine the effect of an irreversible decay channel (photochemistry) on the hole-width. A detailed account of this work will be published elsewhere. ... 

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