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Physical Review Letters

Measurement of a Total Atomic-Radiator-Perturber Scattering Cross Section

Ravinder Kachru, T. J. Chen, Sven R. Hartmann, THOMAS W. MOSSBERG, P. R. Berman

Published Sep 28, 1981• 30 citations
Publisher

Abstract

From work on the $2S\ensuremath{-}2{P}_{\frac{1}{2}}$ transition of atomic $^{7}\mathrm{Li}$, perturbed by noble gases, and use of the photon-echo technique, the first measurement of a "total" atomic-radiator-perturber scattering cross section is reported. The phase-changing, inelastic, and velocity-changing aspects of collisions contribute to this cross section, which is significantly larger than the corresponding pressure-broadening cross section. Typical velocity changes are found to be roughly one percent of the mean thermal speed.

DOI
10.1103/physrevlett.47.902

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From work on the 2S\ensuremath−2P122S\ensuremath{-}2{P}_{\frac{1}{2}}2S\ensuremath−2P21​​ transition of atomic 7Li^{7}\mathrm{Li}7Li, perturbed by noble gases, and use of the photon-echo technique, the first measurement of a "total" atomic-radiator-perturber scattering cross section is reported. The phase-changing, inelastic, and velocity-changing aspects of collisions contribute to this cross section, which is significantly larger than the corresponding pressure-broadening cross section. Typical velocity changes are found to be roughly one percent of the mean thermal speed.
Photon-echo measurements in atomic Na perturbed by He provide the first demonstration of the contribution of velocity-changing-like effects to the transverse relaxation of atoms in superposition of two states even when the states follow different post-collision trajectories. The apparent anomaly that broadening cross sections derived from either absorption line widths or photon-echo relaxation measurements are smaller than the total cross section for scattering of atoms in either pure state is explained.
A measurement is reported of the velocity dependence of the total cross section for Yb optical radiator-Xe perturber collisions in which the active atom is in a superposition of dissimilar (SSS and PPP) states. The total cross section is found to vary with relative velocity in a simple manner, consistent with van der Waals scattering as the dominant interaction for this nonclassical system.
We implement the Raman echo for the first time in collision studies to measure the noble-gas-induced broadening of the $6{P}_{\frac{1}{2}}\ensuremath{-}6{P}_{\frac{3}{2}}$ transition of atomic thallium. Except in the case of He, the measured broadening cross sections He 59(2), Ne 67(2), Ar 124(4), Kr 167(5), and Xe 204(6) A˚2{\mathrm{\AA{}}}^{2}A˚2 (T=840T=840T=840 K), agree with those calculated assuming a pure van der Waals collisional interaction. Our measurements, sensitive to collisionally induced changes in axial velocity of \ensuremath{\gtrsim} 300 cm/sec, reveal that collisional velocity changes of that magnitude are not important in T1-noble-gas collisions.
Absolute velocity-resolved total integral cross sections have been measured for collisions of helium singlet (2 1 S 0 ) and triplet (2 3 S 1 2) metastable (He*) atoms with ground-state helium, neon, and argon atoms in the thermal velocity range of 1.0-3.5*10 5 cm s -1 . Additional measurements on the He*-Ne system with a large input aperture at the detector to suppress the sensitivity of the apparatus to elastic scattering failed to show the previously predicted (Arathoon) sharply rising velocity structure in the inelastic excitation transfer cross sections.