MULTIPERTURBER EFFECTS IN THE FARADAY SPECTRUM OF RB ATOMS IMMERSED IN A HIGH-DENSITY XE GAS

We have measured the D-1 and D-2 Faraday spectrum and absorption spect rum of Rb atoms immersed in high-density Xe buffer gas in the range n( Xe) = 0.8-4.5X10(20) cm(-3). We find that the shape of the Faraday spe ctrum obeys the Becquerel relation over this whole density range; howe ver the relative strength of the Faraday effect compared to absorption changes rather abruptly near n(Xe) = 1X10(20) cm(-3). This is ascribe d to the onset of a many-body nature (overlapping collisions) of the R b:Xe line broadening; the number of perturbers within the Weisskopf sp here is unity at n(?)(Xe) similar to 1X10(20) cm(-3).