Calculation of observed signals

Let the cw exciting light be weak in the sense that one may neglect all the multipole moments in the ground state, except for the equilibrium 

Substituting (4.17) into (2.24), we are able to calculate the intensity of radiation for any geometry and polarization of excitation, as determined by q(E), and also the observations, as determined by q(E7), for all types of transitions (taken into consideration by respective Clebsch-Gordan coefficients with A, A7) the necessary numerical values of and 

It is essential that here the difference between Jy and Jj be determined only by the difference in sign with which bp 2 enter the equations. This difference is determined by the sign of the components 2 for f — 7r/2 and gf = 0, respectively see Table 2.1 (here 0 = 7r/2). On this basis, and applying (2.15), one can see that the dependence of Jy — I on the magnetic field is determined only by the action of B on the Re6/ 2, 

At the same time, as follows from (4.18) and from (4.19), the sum ly +I does not contain any transversal components where Q 0, i.e. it does not depend on the magnetic field. The full expression for the degree of polarization as obtained from (4.18) and (4.19) is of the form 

The origin of this formula can be understood from the form of expansion (2.14) if one remembers that only transversal spherical functions Ykc q are ( -dependent see (B.l), Appendix B. In other words, the shape of the figures in Fig. 4.2 on increase of the magnetic field is not conserved, and the symmetry of the distribution is connected to the transition from the situation when coherence in the J-distribution is present, Fig. 4.2(a) down to the fully incoherent case in Fig. 4.2(e). Hence in this case one can speak about the destruction of coherence by a magnetic field, contrary to the case in Fig. 4.1(6). 

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As example of the employment of the density matrix method for calculation of observable signals, we propose to consider the quadratic Stark effect in the simplest case of the 1S states of molecules possessing a constant electric dipole moment dp. In an electric field the magnetic sublevel M of a rotational state J of such a molecule acquires additional energy [374] ... 

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