Optical Detection of Magnetic Resonance in Alkali Metal Vapor

TLDR

The paper discusses two types of rf magnetic resonance experiments involving optical pumping in alkali vapor, recently suggested by Dehmelt. The authors propose that this technique could be used for magnetic‑field measurements and for determining atomic constants of alkali metal isotopes. They describe two rf magnetic resonance methods—monitoring transmitted light intensity at resonance and detecting high‑frequency modulation in a cross beam—using optical pumping of alkali vapor, modeling the system phenomenologically with Bloch‑like equations that incorporate light‑induced time constants and a cross‑beam term that does not alter resonance shape, and they detail the apparatus and experimental conditions under which signals were observed. The study shows that changes in transmitted light intensity correlate with spin‑system observables, explaining the high‑frequency modulation, and that the derived Bloch‑like equations—modified to include light‑induced time constants and a cross‑beam term that does not affect.

Abstract

This paper discusses two types of rf magnetic resonance experiments involving optical pumping in alkali vapor which have recently been suggested by Dehmelt. These experiments are, respectively, observation of a change of intensity at resonance of the transmitted pumping light, and observation of high-frequency intensity modulation in a second light beam (the "cross beam") incident at an angle to the first. The method of pumping used here is reviewed, together with some of the special assumptions on which it is based. The function of the light in monitoring population differences is treated as a separate matter from the pumping function; it is shown that the observed changes in transmitted light intensity can be correlated in a simple way with other observables of a spin system, and this leads to a simple explanation of the high-frequency modulation effects. A system of spin-\textonehalf{} particles subject to optical pumping and monitoring is then treated phenomenologically. The resulting equations have the same form as Bloch's equations except that (1) the time constants must include effects of the incident light, and (2) there is an additional term due to the cross beam which, however, is shown to have no effect on the shape of the resonance.The apparatus is described, together with experimental conditions under which signals have been observed. Possible applications of the technique include magnetic-field measurements, and studies of atomic constants of alkali metal isotopes.