Doppler dephasing

The linewidths are quite small, roughly 10 kHz, and are caused by a Doppler dephasing as the molecules with a given polarization phase move into a region of space where they would have a different phase. There is in addition a splitting of each line ( 25 kHz) caused by Doppler effects. Nonetheless the resolution is nearly as good as in the electric resonance experiments, allowing precision rotational constants and nuclear hyperfine interactions to be measured. 

Vp-(Xp/Xp) Vp, Vp V(2kgT/m), kg is Boltzman s constant, T is the teitperature and m is the atomic mass. Here Xp-X./27tVp is the normal Doppler dephasing time and Xp is the excitation pulse width and we have assumed Xp Xp. But first we... 

Since the macroscopic polarizations are determined by optical coherences induced in the sample, their observation is restricted by Doppler dephasing, and the spectral resolution of the polarization beats is limited to the Doppler linewidths. In comparison with that quant am-beats are nearly imaffected by inhomogeneous broadening and therefore they are appropriate for high resolution level splitting measurements. 

Comparison of measured and calculated signal shows that a very satisfactory explanation of the observed signal form is achieved. The beat structure can be understood in terms of atomic coherence between substates yielding an amplitude modulation of optical coherence. The fast decay is mainly determined by Doppler dephasing, however, is also slightly influenced by the excited state splitting frequency. 

Chapter 3 is devoted to pressure transformation of the unresolved isotropic Raman scattering spectrum which consists of a single Q-branch much narrower than other branches (shaded in Fig. 0.2(a)). Therefore rotational collapse of the Q-branch is accomplished much earlier than that of the IR spectrum as a whole (e.g. in the gas phase). Attention is concentrated on the isotropic Q-branch of N2, which is significantly narrowed before the broadening produced by weak vibrational dephasing becomes dominant. It is remarkable that isotropic Q-branch collapse is indifferent to orientational relaxation. It is affected solely by rotational energy relaxation. This is an exceptional case of pure frequency modulation similar to the Dicke effect in atomic spectroscopy [13]. The only difference is that the frequency in the Q-branch is quadratic in J whereas in the Doppler contour it is linear in translational velocity v. Consequently the rotational frequency modulation is not Gaussian but is still Markovian and therefore subject to the impact theory. The Keilson-... 

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