Quantum-beat effect

The above three-vnode expression approximates the more exact expression Eq. 54 very well, but does not show the quantum beat effect. 

Fig. 9.3 Mossbauer spectra (A q = 2 mm s ) in the energy domain and in the time domain. High effective thickness t ff appears in the energy domain as line broadening and in the time domain as dynamical beats which are superimposed over the quantum beats. (Taken from [7])...

Fig. 9.16 Time-dependent NFS of [Fe(tpa)(NCS)2] recorded at 108 K. The two curves represent comparison of a coherent vs incoherent superposition of the scattering from 50 % LS and 50 % HS iron(II) characterized by their corresponding quantum beat pattern. The effective thickness of the sample was =18. (Taken from [42])...

The nature of the radiative decay in the resonance and in the statistical limits was considered by Berry and Jortner,7 who examined the interference effects in the radiative decay of coherently excited states. Quantum beat signals can be observed and used to analyze close-lying molecular... 

Level crossing spectroscopy has been used by Fredriksson and Svanberg44 to measure the fine structure intervals of several alkali atoms. Level crossing spectroscopy, the Hanle effect, and quantum beat spectroscopy are intimately related. In the above description of quantum beat spectroscopy we implicitly assumed the beat frequency to be high compared to the radiative decay rate T. We show schematically in Fig. 16.11(a) the fluorescent beat signals obtained by... 

The next phenomenon to be discussed here is the energy gap dependence. To demonstrate this effect, the probing frequency is fixed at the peak positions of the induced absorptions to reduce complications from the stronger quantum beats. Shown in Figure 5.14 is the case when the energy gap is increased to 200 cm-1. The ET dynamics is less efficient than the case of 20 cm-1 gap. This is reasonable because in the case of single displaced mode, the smaller the energy gap, the better the resonance between the... 

In spite of the apparent obviousness of the beat effect in optical radiation at pulsed excitation, it was only registered and studied comparatively recently. At the beginning of the 1960s Aleksandrov [3] and, independently, Dodd and coworkers [119] discovered beats in atomic emission. It may be pointed out that this, and the related phenomenon of beat resonance, was predicted by Podgoretskii [313], as well as by Dodd and Series [118]. The phenomenon was treated on the basis of well-known fundamental concepts on coherent superposition of states, and was named accordingly quantum beats. These ideas are amply expounded in reviews and monographs [4, 5, 6, 71, 96, 120, 146, 182, 188, 343, 348, 388]. 

Silverman, M.P., Haroche, S. and Gross, M. (1978). General theory of laser-induced quantum beats. I. Saturation effects of single laser excitation, Phys. Rev. A, 18, 1507-1516. 

The development of the picosecond-jet technique is presented. The applications of the technique to the studies of coherence (quantum beats), photodissociation, isomerization and partial solvation of molecules in supersonic-jet beams are detailed with emphasis on the role of intramolecular energy redistribution. Experimental evidence for intramolecular threshold effect for rates as a function of excess molecular energy is given and explained using simple theory for the redistribution of energy among certain modes. Comparison with R.R.K.M. calculation is also made to assess the nature of the statistical behaviour of the energy redistribution. 

It is not heretical to consider the electromagnetic vacuum as a physical system. In fact, it manifests some physical properties and is responsible for a number of important effects. For example, the field amplitudes continue to oscillate in the vacuum state. These zero-point oscillations cause the spontaneous emission [1], the natural linebreadth [5], the Lamb shift [6], the Casimir force between conductors [7], and the quantum beats [8]. It is also possible to generate quantum states of electromagnetic field in which the amplitude fluctuations are reduced below the symmetric quantum limit of zero-point oscillations in one quadrature component [9]. 

Ishii, K., Takeuchi, S., Tahara, T., Pronounced Non Condon Effect as the Origin of the Quantum Beat Observed in the Time resolved Absorption Signal from Excited state cis Stilbene, J. Phys. Chem. A 2008, 112, 2219 2227. 

The second major section (Section III), comprising the bulk of the chapter, pertains to the studies of IVR from this laboratory, studies utilizing either time- and frequency-resolved fluorescence or picosecond pump-probe methods. Specifically, the interest is to review (1) the theoretical picture of IVR as a quantum coherence effect that can be manifest in time-resolved fluorescence as quantum beat modulated decays, (2) the principal picosecond-beam experimental results on IVR and how they fit (or do not fit) the theoretical picture, (3) conclusions that emerge from the experimental results pertaining to the characteristics of IVR (e.g., time scales, coupling matrix elements, coupling selectivity), in a number of systems, and (4) experimental and theoretical work on the influence of molecular rotations in time-resolved studies of IVR. Finally, in Section IV we provide some concluding remarks. 

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