Experimental Evidence for Light-Shift Induced Zero-Field Level Crossing (“Optical Hanle Effect”)

Abstract

Two types of zero-field level crossing (Hanle effect) have been observed in the past using either a static magnetic field or a static electric field [1]. The physical basis of the phenomena is found in the lifting of the m-state degeneracy by the external static field (Zeeman effect or Stark effect) which breaks down the zero-field quantum interference. A lot of lifetimes and relaxation rates have been measured for atomic and molecular species by this method with broad-band coherent excitation of the fluorescent levels and magnetic field scanning. An optical analogue of the Hanle effect has been recently proposed where the light-shift induced by a high power laser beam replaces the level shift produced by the static fields [2]; the dynamic Stark shift plays the same role as the Zeeman shift in the magnetic Hanle effect or as the Stark shift in the electric Hanle effect. The theory of the so-called “optical Hanle effect” has been previously worked out for a (J=0→1→0) three-level system [2]. In this letter, we present the first experimental observation of the light-shift induced zero-field level crossing in a (J=0→1) two-level system of Ba I, as well as the main results of the corresponding calculations.