Broadened transition

Fig. 13 a-c. Hole-burning saturation of two doppler broadened transitions sharing a common lower level... 

The broadened transition response is a general characteristic of power feed polymers as evidenced by the results of stiffness-temperature, stress relaxation and dynamic mechanical measurements. 

The principle of the experiment is illustrated by Fig. 12. On the left-hand side the absorption band of an inhomogeneously broadened transition, e.g., the OH-stretching band in different H-bonded local environments, is depicted schematically. Structures with different OH-O bond angles and/or 0-0 bond lengths show up in the spectrum with different OH frequencies linear bonds and shorter bond length correspond to larger red shifts... 

It can be seen from that figure that the -transitions of the two component materials are separated by about 20 degrees. If the blend is an immiscible mixture, it is expected that there would be two transitions observed which are 20 degrees apart, or, at least, it is expected that a single significantly broadened transition would be observed. 

Traditionally the two-pulse photon-echo of a two-level system is described in terms of dynamics where there is a separation of the frequency fluctuations into two widely separated time scales, one of which is much faster and the other much slower than the time that characterizes the inhomogeneous distribution of frequencies. This gives rise to a hxed distribution of homogeneously broadened transitions for each spectral transition of the solute. The echo electric held generated from two very short pulses interacting with a molecule but separated by an interval x is, apart from constant factors, given by... 

Constructive and destructive interference of bound-bound vs. free-bound transition amplitudes on opposite sides of linecenter of a predissociatively broadened transition result in an asymmetric Fano type line shape, characterized by Fano s index qv. The absorption cross-section in the case of dissociation has the form... 

In Vol. 1, Sect. 3.6 we saw that the saturation of homogeneously broadened transitions with Lorentzian line profiles results again in a Lorentzian profile with the... 

We will now discuss saturation of inhomogeneous line profiles. As an example we treat Doppler-broadened transitions, which represent the most important case in saturation spectroscopy. 

Fig. 2.4 Velocity-selective saturation of a Doppler-broadened transition (a) the Bennet hole in the lower- and the Bennet peak in the upper-state population distribution Ndv ). (b) Saturated absorption profile when the saturating laser is tuned across the Doppler-profile of a molecular transition dashed curve)...

In the case of T2, the results for incoherent light are entirely the same as those for short pulse except that the T2 decay characteristic in the correlation trace appears symmetrically with respect to x for homogeneously broadened transition. In the case of Tj = T2, however, the appearance of T -dependent background and the modification of relaxation decay due to the Ti effect occur for incoherent light, while the results are independent of for short pulse input. These features complicate the interpretation of the results for incoherent light. But they still serve for the determination of T2, because the decay characteristics are dominantly governed by T2. All these behaviors can well be explained physically by... 

Photon echoes Resonant interaction with inhomogeneously broadened transition pulse duration less than dephasing time two pulses spaced by echo time r, with pulse areas of 7t/2 and 7t, respectively... 

If both levels a) and b) decay with the relaxation constants ya and y, respectively, the line profile of the homogeneously broadened transition a)... 

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