Abstract

Experiments exploiting similarities for coherence collisional evolution in velocity space and in M space are reported. Generally, there is a total outgoing rate from any state and incoming rates (kernels) from neighboring states. Collision-induced velocity changes, ΔV, are studied with lasers by measuring the Doppler frequency Δ V/λ (λ = optical wavelength). To obtain information about coherence M transfer, it is only necessary to associate a frequency with each ΔM. This idea is demonstrated by measuring two-pulse photon echo intensity I_e for ¹³CH₃F in a small dc Stark field. Acoustooptic modulation of infrared cw laser radiation, polarized parallel to the Stark field, is used to excite a number of uncoupled M → M transitions on the R(4,3) line. Each transition has a resonance frequency, vo + M· vs (vs is M = 1 Stark shift, Hz). A most remarkable result is obtained for large echo delays T with ΔVT/λ >> 1, all ΔV. The shape of the curve ln[ I_e(o)/ I_e(V)] vs Stark voltage V tends to that of the dominant coherence ΔM transfer kernel itself. Physically this arises because, for large T, the macroscopic coherence is preserved only for collisions where the frequency changing due to M transfer compensates the Doppler shift due to the ΔV, i.e., Δ V/λ + ΔM-·vs = 0. Generalizations are discussed.

© 1985 Optical Society of America