Local field effects in the spectroscopy of Cs atoms trapped in solid 4 He

In this paper we have described several experimental observations of matrix effects in the optical and magneto-optical properties of paramagnetic Cs atoms in solid 4 He matrices. First qualitative explanations of the findings in terms of local field effects are presented. The bcc phase of solid 4 He can be used as a trap for foreign atoms with long storage times, in which the isotropy of the trapping sites allows high resolution spin physics experiments to be performed. On the other hand, we have given first evidence that paramagnetic spin polarized atoms can be used as a highly sensitive probe for the investigation of local fields in hcp He matrices