Two methods for nuclear spin determination in collinear laser spectroscopy : classical r.f. magnetic resonance and observation of the Larmor precession

Abstract

Measurement of nuclear spin in the collinear laser spectroscopy method has been investigated using a fast sodium atomic beam excited collinearly by a C.W. single mode dye laser beam. The atomic magnetic moments are first aligned by optical pumping process, then they interact with a static magnetic field H0. The magnetic alignment of the atomic system just at the exit of the magnetic field is monitored by the laser induced fluorescence. Upon varying the amplitude of H0, the fluorescence signal presents a fringed structure. This structure is due to the Larmor precession of the aligned magnetic moments around H0, and therefore it is a signature of the spin involved. The modulation patterns corresponding to different relative orientations of H0 and light polarization direction, are fitted by an analytical formula. In a second step, a classical magnetic resonance experiment with a static magnetic field and a radiofrequency field has been performed. The monocinetic character of our fast atomic beam allowed us to observe, even at high r.f. power, resonances line shapes in agreement with the Majorana formula.