Forward scattering, quantum-beats

When, however, phonons of appropriate energy are available, transitions between the various electronic states are induced (spin-lattice relaxation). If the relaxation rate is of the same order of magnitude as the magnetic hyperfine frequency, dephasing of the original coherently forward-scattered waves occurs and a breakdown of the quantum-beat pattern is observed in the NFS spectrum. 

H. Harde, H. Butggraf, J. Mlynek, W. Lange, Quantum beats in forward scattering subnanosecond studies with a mode-locked dye laser. Opt. Lett. 6, 290 (1981)... 

Fig. 2 Experimental set-up for measurement of Na fine structure quantum-beats in forward scattering.

In general, the time dependence of the nuclear forward scattering comprises both quantum and dynamical beats, as depicted in Fig. l.lOf for the case of electric quadrupole interaction. If the resonances are well separated, the time development of the amplitude of nuclear forward scattering from a sample of thickness d can be expressed as [22]... 

Fig. 1.10 Coherent excitation and coherent de-excitation of the nucleus for the nuclear forward scattering and the nuclear Bragg scattering. Coherent de-excitation of the resonant scattering creates the quantum beat with a frequency of Q...

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