Giant modification of atomic transition probabilities induced by a magnetic field: forbidden transitions become predominant

The magnetic field-induced giant modification of probabilities for seven components of 6S(1/2), F-g = 3 -> 6P(3/2), F-e = 5 transition of the Cs D-2 line, forbidden by selection rules, is observed experimentally for the first time. For the case of excitation with circularly polarized laser radiation, the probability of a F-g = 3, m(F) = -3 -> F-e = 5, m(F) = -2 transition becomes the largest of 25 transitions of the F-g = 3 -> F-e = 2,3,4,5 group in a wide-range magnetic field of 200-3200 G. Moreover, the modification is the largest among D-2 lines of alkali metals. A half-wave-thick cell (the length along the beam propagation axis L = 426 nm) filled with Cs has been used in order to achieve sub-Doppler resolution, which allows the large number of atomic transitions that appear in the absorption spectrum to be separated when an external magnetic field is applied. For B > 3000 G the group of seven transitions F-g = 3 -> F-e = 5 is completely resolved and is located at the high frequency level of F-g = 3 -> Fe = 2,3,4 transitions. The applied theoretical model describes very well the experimental curves.