We have measured the He-, Ne-, and Ar-induced relaxation properties of the $3S\ensuremath{-}nS$ ($3S\ensuremath{-}nD$) superposition states of atomic sodium, where
n ranges from 5 to 20 (4 to 34). The measurements were made using the trilevel echo effect. We find that the effective collisional cross section first increases (as a function of
n) at low
n, and then decreases to a lower asymptotic limit at high
n. This behavior is similar to that previously observed for the $3S\ensuremath{-}nP$ series. We also find that the difference between the collisional cross sections for
S and
D series superpositions closely approximates the inelastic collision cross sections measured elsewhere for the
d states. A theoretical description of the trilevel echo effect used to make the measurements is presented.
We have made comprehensive measurements of the noble-gas-induced (He, Ne, Ar, Kr, and Xe) broadening cross sections of the Na $3S\ensuremath{-}nS$ ($3S\ensuremath{-}nD$) transitions, from
n=5to38 (
n=4to40). These measurements were made using the trilevel-echo technique and are an extension and refinement of our earlier work. We find that the cross sections increase as the geometric cross section at low values of
n, and then, at a value of
n which depends on the particular noble gas, begin to decrease and eventually reach an asymptotic value at high
n. The broadening cross sections for the nearly degenerate
D states are significantly larger than those for the
S states and clearly show the effect of
l-changing collisions. We also compare our measured
S-state broadening cross sections with the cross sections calculated using the theory of Omont and find good qualitative agreement.
A variant of the trilevel-echo effect is observed and utilized to measure the effective cross section for broadening of the $3{P}_{\frac{1}{2}}\ensuremath{-}3{P}_{\frac{3}{2}}$ 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 $3{P}_{\frac{1}{2}}\ensuremath{-}3{P}_{\frac{3}{2}}$ 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)
A˚2, Ne 120(12)
A˚2, Ar 234(23)
A˚2, Kr 266(27)
A˚2, and Xe 311(31)
A˚2. With He as the perturber, the cross section for broadening of the $3{P}_{\frac{1}{2}}\ensuremath{-}3{P}_{\frac{3}{2}}$ 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.
We report the first study of molecular-perturber-induced broadening of forbidden ground-to-Rydberg-state transitions. The
N2- and CO-induced-broadening cross sections for the $3S\ensuremath{-}\mathrm{nS} (\mathrm{nD})$ transitions of sodium have been measured for values of
n, the principal quantum number of the upper state, ranging from 4 to 41. These measurements, performed using the trilevel echo technique, were accomplished at sodium and perturber densities of ${10}^{\ensuremath{-}6}$ and 1 torr, respectively. The broadening rates, observed in the present experiment, differ in some respects from those observed previously with noble-gas perturbers. These differences, which presumably arise because of the presence of accessible internal degrees of freedom in the
N2 and CO perturbers (and in the case of CO also because of its permanent electric-dipole moment), are most clearly displayed in $3S\ensuremath{-}\mathrm{nS}$ transitions. Previous work has shown that with noble-gas perturbers the $3S\ensuremath{-}\mathrm{nS}$ broadening cross sections display a dramatic increase at low values of
n; they then decline at intermediate values of
n, and at high
n they approach a limiting value. In the present experiment we find that the initial increase in $3S\ensuremath{-}\mathrm{nS}$ broadening cross sections with
n is relatively small and more gradual. For high
n, the broadening cross sections become approximately constant. As is the case with noble-gas perturbers, the broadening of $3S\ensuremath{-}\mathrm{nD}$ transitions is generally larger than the broadening of the corresponding $3S\ensuremath{-}\mathrm{nS}$ transitions. With CO as a perturber, an unexplained irreproducibility in the broadening cross sections of high-
n $3S\ensuremath{-}\mathrm{nD}$ transitions is observed. One explanation has to do with the CO-induced frequency shifts being unusually large and exceeding the spectral width of our excitation lasers.