We have measured Ar- and Kr-induced broadening of the Ca4s21S-4snp XP (6£n£10) and 4s21S-3d4plP transitions by means of the total absorption method. In this regime of n, the broadening cross section increases to its maximum value with n and then decreases. The maximum value is 28 x 10-14 cm2 at n=8 for Ar and 72 x 10-14 cm2 at n=9 for Kr. Assuming that the interatomic potential is described as a superposition of the Fermi potential and the polarization potential, we have calculated the cross section on the basis of the classical broadening theory. This calculation agrees well with both the present result and that for the Na 3S-nS transitions measured by Kachru et al. by means of the trilevel-echo technique.
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