Resonance excitation lifetime

Thus, in summary, it appears that the LFE mechanism predicts that for dyes in resonance the Raman spectrum will be enhanced to the same degree as normal scatterers, except when a typical resonance excitation profile is not observed. This conclusion is in contradiction to that expressed in Reference 240. The excessive sensitivity of the model presented there to lifetime changes is, to a large part, due to the simple two-state description of the excited... 

The temporal response of the third-order nonlinear optical susceptibility in poly(PTS) crystal was determined by time-resolved degenerate four-wave mixing (DFWM) by Carter and coworkers. The excited lifetime T ws measured to be 1.8 0.5 ps at 652 nm in the resonant region. The values of phase relxation time T2 measures by Hattori and Kobayashi for a cast film of poly(3BCMU) were 30 and 90 fs for the respective incident... 

As a matter of fact, under quasi-resonant excitation of single rotational levels in diatomic molecules, the observed fluorescence decays are exponential. For weakly perturbed levels yv = y, but in the case of a strong perturbation, the lifetimes of mixed levels are anomalously long. Such an effect has been observed for the N2 (r = 1) state by Dufayard et al. (1974) (Fig. 11) and for the CO A ri(D = 0) state by Provorov et al. (1977). 

The above equations show the importance of resonance, but are unrealistic since will be limited by relaxation processes in the excited state. Thus a damping factor inversely related to the excited-state lifetime must be introduced. On resonance, excited-state relaxation will deter-... 

One possible explanation for this enhanced energy transfer could be related to the nature of polymer excitons and the fact that the Si02 Au nanoparticles can exhibit greatly enhanced local field intensities. Since metal nanoparticle resonances have excitation lifetimes of only a few picoseconds, the donor-... 

Figure Al.6.15. Schematic diagram, showing the time-energy uncertainty principle operative in resonance Raman scattering. If the incident light is detuned from resonance by an amount Aco, the effective lifetime on the excited-state is i 1/Aco (adapted from [15]).

Figure 20. Energy levels of neutral sodium atom mostly involved in the resonant incoherent 2-photon excitation for the polychromatic LGS. Wavelengths (nm), lifetimes (ns) and homogeneous widths (MHz).

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