Zeeman quantum beats

Fig. 16.10 Quantum beat signals of high lying 2D states of Na obtained by time resolved selective field ionization. The variation of the beat frequency with principal quantum number is shown. Several quantum beat frequencies appear due to a Zeeman splitting of the fine structure levels in the earth s magnetic field (from ref. 43).

It is this term that describes magnetic ( Zeeman ) quantum beats in the form of intensity modulation with frequency ojmm -... 

So far we have been discussing magnetic (Zeeman) quantum beats taking place at frequencies of coherent sublevel splitting in an external magnetic field. 

Auzinsh, M.P., Tamanis, M.Ya. and Ferber, R.S. (1986). Zeeman quantum beats during the transient process after optical depopulation of the ground electronic state of diatomic molecules, Sov. Phys.—JETP, 63, 688-693. 

Zeeman quantum beat spectroscopy was used by Gouedard and Lehmann (1979, 1981) to measure the effect of various lu perturbing states on the gj-values [Eq. (6.5.21)] of more than 150 rotational levels of the Se2 B 0+ state (see Section 6.5.2 and Fig. 6.16). In that experiment, the excitation polarization was perpendicular to the applied magnetic field so that quantum beats were observed between nominal B-state components differing in M by 2. The frequencies of these beats increase linearly from 0 MHz at 0 G until the AM — 2 splitting falls... 

The earliest pulsed laser quantum beat experiments were performed with nanosecond pulses (Haroche, et al., 1973 Wallenstein, et al., 1974 see review by Hack and Huber, 1991). Since the coherence width of a temporally smooth Gaussian 5 ns pulse is only 0.003 cm-1, (121/s <-> 121 cm"1 for a Gaussian pulse) nanosecond quantum beat experiments could only be used to measure very small level splittings [e.g. Stark (Vaccaro, et al., 1989) and Zeeman effects (Dupre, et al., 1991), hyperfine, and extremely weak perturbations between accidentally near degenerate levels (Abramson, et al., 1982 Wallenstein, et al., 1974)]. The advent of sub-picosecond lasers has expanded profoundly the scope of quantum beat spectroscopy. In fact, most pump/probe wavepacket dynamics experiments are actually quantum beat experiments cloaked in a different, more pictorial, interpretive framework,... 

Stark and Zeeman polarization quantum beats are discussed in Section 6.5.3. An external electric or magnetic field destroys the isotropy of space. As a result, the amplitudes for two transition sequences J", M" — J, M = M" 1 —> J ", M" interfere, and the intensity of X or Y (but not Z) polarized fluorescence is modulated at (Fj M =M"+i — Ejim =M"-i)/h. However, it is not necessary to destroy the isotropy of space in order to observe polarization quantum beats. 

Fig. 7.11 Zeeman quantum beats observed in the fluorescence of Yb atoms in a magnetic field after pulsed excitation at A = 555.6 nm [871]...

The two Zeeman components of an atomic level (L = 1, 5 = 1/2, / = 1/2) are coherently excited by a short laser pulse. Calculate the quantum-beat period of the... 

G. Herzberg, Molecular Spectra and Molecular Structure (van Nostrand, New York, 1950) N. Ochi, H. Watanabe, S. Tsuchiya, RotationaUy resolved laser-induced fluorescence and Zeeman quantum beat spectroscopy of the state of jet-cooled CS2. Chem. Phys. 113,... 

M. Dubs, J. Muhlbach, H. Bitto, R Schmidt, J.R. Huber, Hyperfine quantum beats and Zeeman spectroscopy in the polyatomic molecule propynol CHOCCHO. J. Chem. Rhys. 83,3755 (1985)... 

B. J. Dalton, Cascade Zeeman quantum beats produced by stepwise excitation using broad-line laser pulses. J. Rhys. B 20, 251, 267 (1987)... 

The theoretical description of the quantum-beat structure in terms of oscillating population differences between Zeeman substates of different fine structure levels gives very satisfactory explanation for the appearance and form of the observed signal. 

Because quantum-beat spectroscopy offers Doppler-free spectral resolution, it has gained increasing importance in molecular physics for measurements of Zeeman and Stark splittings or of hyperfine structures and perturbations in excited molecules. The time-resolved measured signals yield not only information on the dynamics and the phase development in excited states but allow the determination of magnetic and electric dipole moments and of Lande g-factors. 

Because of the special properties of the exponential function the light decays with the same time constant r as the population decay. The light decay can be followed by a fast detector connected to fast, time-resolving electronics. If the excited state has a substructure, e.g. because of the Zeeman effect or hyperfine structure, and an abrupt, coherent excitation is made, oscillations (quantum beats) in the light intensity will be recorded. The oscillation frequencies correspond to the energy level separations and can be used for structure determinations. We will first discuss the generation of short optical pulses and measurement techniques for fast optical transients. 

Fig.9.32. Zeeman quantum beats for the resonance line in ytterbium [9.126]...

Advanced EMR methods may be used to conduct quantitative measurements of nuclear hyperfine interaction energies, and these data, in turn, may be used as a tool in molecular design because of their direct relation to the frontier orbitals. The Zeeman field dependence of hyperfine spectra enables one to greatly improve the quantitative analysis of hyperfine interaction and assign numeric values to the parametric terms of the spin Hamiltonian. Graphical methods of analysis have been demonstrated that reduce the associated error that comes from a multi-parameter fit of simulations based on an assumed model. The narrow lines inherent to ENDOR and ESEEM enable precise measures of peak position and high-resolution hyperfine analyses on even powder sample materials. In particular, ESEEM can be used to obtain very narrow lines that are distributed at very nearly the zero-field NQI transition frequencies because of a quantum beating process that is associated with... 

In Fig. 9.29 an example of Zeeman quantum beats is shown. The geometries for excitation and detection are the same as for a recording of the Hanle effect (Sect. 7.1.5). The signal is also a AM = 2 phenomenon. Zeeman quantum beats can also be explained semiclassically using the same model as... 

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