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

Working on the 2S-2P/sub 1/2/ transition of atomic /sup 7/Li, perturbed by noble gases, and using 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.