Relaxation, vibrational inhomogeneous broadening

The last mentioned dynamical capability of lasers is in its infancy. It is possible in principle to make optical measurements which are analogous to coherent NMR measurements, and thereby to observe homogeneous linewidths in inhomogeneously broadened systems, to measure optical or vibrational Ti and T2 relaxation times directly, and to observe quantum recurrences. 

Figure 22 (a) Model calculation for the stimulated photon echo signal of the cyclic model peptide (cydo-Mamb-Abu-Arg-Gly-Asp) based on its known structures. The same coupling constants were employed as in the model simulations of the 2D-IR spectrum in Fig. 16. The parameters for homogeneous broadening (T2 = 0.7 ps), vibrational relaxation (Tj = 1.2 ps), and inhomogeneous broadening (diagonal disorder 20 cm-1) were also the same. The pulse duration of the laser pulses was set to 120 fs. (b) The same calculation as in (a), but with -shaped laser pulses and neglecting the inhomogeneous broadening. A sharp coherence spike now occurs at T = r = 0, which is not seen experimentally.

Although the band intensity in Eqn 24.1 is written with an infinitesimally narrow bandwidth (via the Dirac delta function), in practice the delta function is replaced by a more realistic band shape factor with a finite bandwidth. There are several contributions to the bandwidth including vibrational relaxation and dephasing, inhomogeneous broadening, and lifetime broadening. Since each of these separately is difficult to calculate exactly, the bandwidth is often represented by a phenomenological function based on an appropriate model. Bandwidth analyses are most... 

Figure 2 Emission spectrum fit with Equation (1). The value of E, the average of medium frequency vibrational modes contributing to nonradiative relaxation, ht/, the degree of excited state distortion, proportional to the Huang Rhys factor S, and the degree of inhomogeneous broadening of vibronic...

Isotropic scattering In addition to the dephasing time T2, the correlation time rc of the purely vibrational relaxation process can be measured, providing quantitative information on the question of homogeneous/inhomogeneous line broadening. 

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