Time Characteristics of Spin Polarization in Magnetic Resonance System
In this study,the temporal characteristics of the polarization process of rubidium atoms in a laser pumping magnetic resonance system under the influence of a constant magnetic field and radiofrequency(RF)field are analyzed both theoretically and experimentally.A simple optical magnetic resonance experiment platform has been established based on rubidium atoms in our experiment.By applying a constant magnetic field along the z-direction,Zeeman splitting was induced in rubidium atoms.The frequency of the laser propagating along the z-direction was locked to the saturated absorption spectrum of 85Rb atoms'D1 line transition 52S1/2,Fg=3→52P1/2,Fe=2,and converted into left circularly polarized beam to polarize the atoms.This laser beam was also used as a probe beam to detect the polarization state of rubidium atoms.Meanwhile,a switch-controlled resonant RF field was applied along the x-direction to induce transitions between atomic polarization states.Here,we monitored the polariza-tion state of rubidium atoms by recording the transmission intensity of the probe beam.When the RF field is turned off,rubidium atoms are polarized solely by absorbing left circularly polarized probe beam.The maximum intensity of the transmitted beam indicates that maximum polarization can be achieved in the experiment.When the resonant RF field is activated,the polarization state is disrupted,causing the atoms to depolarize and reabsorb the probe beam,resulting in a decrease in the intensity of the transmitted beam.The minimum intensity of the transmitted beam indicates an equilibrium between the magnetic resonance depo-larization process and the optical pumping polarization process.The RF current amplitude was set to 1.8 mA,and the probe beam power increased from 70 μW to 200 μW.The time evolution of transmission beam was observed by periodically switching the current amplitude of the RF coil.Experimental results showed that the power of the probe beam influenced the polarization pro-cess of rubidium atoms,with higher probe beam power resulting in shorter polarization completion time.Numerical analysis based on density matrix theory for a three-level system strongly supported the provided experimental data,aiding further investi-gation into the dynamic evolution of the magnetic resonance system.
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