Noble-gas-induced collisional broadening of the3P12−3P32transition of sodium measured by the trilevel-echo technique

A variant of the trilevel-echo effect is observed and utilized to measure the effective cross section for broadening of the $3P_{\frac{1}{2}}-3P_{\frac{3}{2}}$ transition of sodium by the noble gases. The cross section measured here should be the same as the broadening cross section obtained from a direct measurement of the collisionally broadened $3P_{\frac{1}{2}}-3P_{\frac{3}{2}}$ transition linewidth (if such a measurement were possible). The new echo, the "inverted-difference-frequency" (IDF) trilevel echo, is well suited to the study of transitions between excited states of the same parity. At 400 K the measured broadening cross sections are He 115(12) ${\mathrm{\AA }}^2$, Ne 120(12) ${\mathrm{\AA }}^2$, Ar 234(23) ${\mathrm{\AA }}^2$, Kr 266(27) ${\mathrm{\AA }}^2$, and Xe 311(31) ${\mathrm{\AA }}^2$. With He as the perturber, the cross section for broadening of the $3P_{\frac{1}{2}}-3P_{\frac{3}{2}}$ transition can be calculated from measured depolarization and fine-structure-changing collision cross sections. With the other perturbers, however, collisional phase changes appear to be important. An intuitive diagrammatic technique for the analysis of echoes is applied to the IDF trilevel echo.