Hanle effect polarization

Due to the fact that the effect of a magnetic field on the ground state angular momenta distribution pa(0, ip) causes changes in the excited state distribution pb(9,(p) (see Figs. 4.9 and 4.10), one may expect to observe the ground state Hanle effect in fluorescence intensity difference I — I or in the degree of polarization V B). Indeed, since we have gj"/yK 2>... 

Fig. 4.11. Hanle effect on the degree of linear polarization V = (/y — Iff/(I + Iff) at (P, f )-excitation 1 - superpositional signal calculated at the same conditions as Fig. 4.10, dots refer to the positions a, b, c, d as in Fig. 4.10 2 - pure excited state signal at x = 0 3 - pure ground state signal at gj> = 0 4 - experimentally measured dependence for Te2 under conditions as given in Fig. 4.6, curve 1, but in the region of weaker magnetic field and at strong pumping (x 3).

This peculiarity in the behavior of polarization of radiation under the electric field effect ought to be easily understood from an analysis of Eq. (5.14). As can be seen, the intensities of the two fluorescence components differ in the sign of the second term, which is proportional to (T2 + w+i)-1- the case of the Hanle effect at increase in magnetic field strength all increase, and the second term becomes... 

The result obtained reflects linear approximation, i.e. manifestation of the usual linear (observable signal is proportional to Tp) Hanle effect (Section 4.2). This contention becomes obvious if we substitute the polarization moments obtained into the expression for fluorescence intensity (5.34) and find the form of the degree of polarization V = (Iy — Ix)/(Iy + Ix) (Fig. 5.8). For instance, for a radiative transition (J = 1) -> (J" = 1), and using Table C.3 for numerical values of 6j-symbols and for values of from Table 2.1, we obtain... 

Auzinsh, M.P. and Ferber, R.S. (1983). Manifestation of the sixth-order polarization moment in the Hanle-effect signal of the electronic ground state of dimers, Opt. Spectrosc. (USSR), 55, 674-675. 

Probably coherent effects in atomic excitation with light were studied first by Wilhelm Hanlc. The very first publication about the effect, which is now called Hanle effect, appeared in Zeitschrift fur Physik as early as in 1924 [1]. In the paper it was shown that the resonance fluorescence of Hg excited with linear polarized light is depolarized by an external magnetic field. That publication docs... 

It is well known that when atoms are excited by a collimated beam of electrons whose energy is at or just above the excitation threshold, the light emitted is strongly polarized. In order to create the atomic polarization necessary for Hanle effect signals using electron bombardment excitation, it is necessary that the electron velocity vector should be perpendicular to the applied magnetic field B. 

The polarization of the fluorescent light. The Hanle effect signal is usually obtained by measuring the intensity of the fluorescent light with polarization vector d emitted in some well-defined direction r. From equations (2.70) and (5.8) it can be shown (Problem 15.4) that the intensity of light with this polarization emitted when an excited atom in the sub-state m> decays to the ground-state sub-level y > is... 

We see that field-dependent terms appear in the denominator of equation (15.27) when m m, i.e. the Hanle effect signal is a direct result of the Hertzian coherence created in the excited state by excitation with coherently polarized light. We can describe the phenomenon as the result of a quantum-mechanical interference between the scattering amplitudes for the two possible routes from the initial ground level sub-state y > to the final sub-state... 

The r.f. magnetic field is assumed to be zero. The polarizations for both a and tt excitation and the amplitude of the Hanle effect signals all tend to zero at high densities,... 

By using circularly and linearly polarized light alternatively in the same geometry, Omont (1965a) was able to measure both Pg and Pg using the Hanle effect in iso-198... 

These experiments are in fact entirely analagous to the Hanle effect or zero-field level-crossing experiments involving excited atoms discussed in Chapter 15. The coherent polarization of the pumping light referred to the quantization axis Oz in Fig.17.12 prepares the atoms in a coherent superposition of ground-state Zeeman sub-levels. The ensemble density matrix now has finite off-diagonal elements... 

It is rather likely that understanding of the anisotropic distribution of the angular momenta of atoms was enhanced by Hanle s [184] discovery in 1924. Hanle observed the effect of the disappearance of linear polarization in fluorescence in a weak magnetic field directed at right angles to the E-... 

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