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Journal of the Optical Society of America B

Effective collinear optical pumping for nuclear spin polarization

Sung Jong Park, T. Shin, Ju Hahn Lee, Gidong Kim, Yong Kyun Kim

Published Sep 3, 2014• 3 citations
Publisher

Abstract

By numerically solving the density matrix equations, we show that the laser frequency ramping method by means of position-dependent Zeeman splitting can efficiently polarize nuclear spin of atoms/ions in an accelerator beamline. This minimizes a quantum phenomenon, coherent population trapping, which limits the optical pumping efficiency in the polarized beamline for radioactive nuclear spin polarization. We consider the Li8 atomic system interacting with two circularly polarized laser beams in the presence of time-dependent magnetic field. From numerical results, we find that optimum frequency ramping allows efficient optical pumping for a short interaction time, e.g., 2 μs.

DOI
10.1364/josab.31.002278

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By numerically solving the density matrix equations, we show that the laser frequency ramping method by means of position-dependent Zeeman splitting can efficiently polarize nuclear spin of atoms/ions in an accelerator beamline. This minimizes a quantum phenomenon, coherent population trapping, which limits the optical pumping efficiency in the polarized beamline for radioactive nuclear spin polarization. We consider the Li8 atomic system interacting with two circularly polarized laser beams in the presence of time-dependent magnetic field. From numerical results, we find that optimum frequency ramping allows efficient optical pumping for a short interaction time, e.g., 2 μs.
Abstract We analyze the polarization of the total angular momentum of alkali atoms in a gas cell with a buffer gas under pumping by monofrequency circularly polarized laser radiation. The mathematical model takes into account the motion of atoms and collisions preserving the nuclear spin under the chaotization of the angular momentum of the outer electron shell, total hyperfine structure, and the Zeeman structure. We analyze the stationary solution to equations for the density matrix of alkali atoms and the effect produced on them by the fraction of inelastic collision in which the quenching of atomic excitation takes place. We consider the contribution of various hyperfine states to the polarization of alkali atoms. The results are compared with the results of the model of instantaneous mixing of populations in the excited state.
The evolution of the hyperfine structure magnetic sublevel populations of 87 Rb and 133 Cs atoms in resonant linearly polarized laser fields is theoretically analyzed. Analytical expressions are obtained for stationary populations of the magnetic sublevels of the ground state 5 2 S 1/2 F g = 1, F f = 2 in 87 Rb and 6 2 S 1/2 F g = 3, F f = 4 in 133 Cs under optical pumping at the F g ↔ F e = F g and F f ↔ F e = F f transitions of the D 2 lines ( n 2 S 1/2 n 2 P 3/2 ) versus the initial populations. The characteristic population stabilization time are obtained by numerical solution for the density matrix equations, depending on the intensity of the laser fields and the detuning of the optical resonance. It is shown that the alternation of the polarization direction of the laser field at the transition F f ↔ F e = F f almost completely transfers atoms to the lower sublevel of the "clock" M1 transition F g M = 0 ↔ F f M = 0 in rubidium and cesium frequency standards, which proportionally increases the signal of the recording system.
We simulated the optical pumping rate of 87Rb atoms with Xe and high-pressure buffer gas in a cubic cell. We calculated absorption cross-section as a function of pumping laser frequency by considering a pressure and Doppler broadening as gas temperature varies from 364 K to 414 K. In a steady state the spin polarization and the atomic population of 87Rb atoms were obtained by optical pumping in each ground state. We calculated the optimum beam waist, linewidth and detuning of pumping beam to achieve higher population of polarized atoms at cell parameters such as temperature, size. We simulated that the optimum beam waist is 0.3 times of cubic cell length at 250 Torr of di-nitrogen and 50 Torr of Xe gas pressure. The optimum laser beam linewidth parabolically increases with increasing the temperature in range of few ten kelvin and it exponentially decrease with increasing the cubic cell length. We also observed that few ten GHz detuned laser frequency increases the optical pumping rate. These numerical results show appropriate experimental parameter as a function of cell temperature and size to get maximum population of spin polarized atoms in given temperature range.
Cs) atoms by applying circularly polarized light at an optimal frequency for electronic transitions from ground to excited states. To enhance control over sublevel populations following optical pumping, we incorporate a radiofrequency (RF) field. This integrated approach enables us to achieve a tailored distribution of atomic sublevel populations with high efficiency. Utilizing the Lindblad master equation, we provide a comprehensive framework for analyzing these dynamics, examining relaxation rates, repopulation processes, and the evolution of cesium Zeeman sublevels. Our findings underscore the effectiveness of the Lindblad master equation in accounting for external field effects and environmental interactions, significantly improving the accuracy and generalizability of optical pumping models. This method holds substantial promise for various applications in optical experiments, including magnetometry and quantum computing, paving the way for future advancements in these fields.
We investigate the population differences between ground-state hyperfine levels (5S1/2,F=2{5S}_{1/2},F=25S1/2​,F=2 and 5S1/2,{5S}_{1/2},5S1/2​, F=1F=1F=1) of an optically pumped 87Rb{}^{87}\mathrm{Rb}87Rb beam in a static magnetic field, taking into account the various kinds of atomic coherence (Zeeman, hyperfine, and optical). The pumping lasers are monochromatic and in resonance with the ${(5S}_{1/2},F=1\ensuremath{\leftrightarrow}{5P}_{1/2}{,F}^{\ensuremath{'}}=1)$ transition. By varying the polarization configuration of the pumping lasers, we find that the pumping efficiency is substantially enhanced when a $\ensuremath{\sigma}$-polarized laser and a $\ensuremath{\pi}$-polarized laser are counterpropagating. In this case, the pumping efficiency remains high even in a weak magnetic field, which explains qualitatively experimental data reported previously from a cesium beam experiment.
Abstract The atomic population trapped in irrelevant atomic states is a limiting factor for sensors based on laser-atom interaction. Using a bi-chromatic light field along with a specific combination of magnetic fields, we show a significant increase in the amplitude ( i.e. , more than seven times) of a two-photon coherent population trapping (CPT) resonance, which can be effectively used for atomic magnetometry. This increase in amplitude can be explained through enhanced optical pumping via the transfer of population to the relevant Zeeman states. Our experimental observations are consistent with the theoretical calculations carried out for a realistic three-level atomic system using density matrix formalism. We further discuss the optimum condition for enhanced optical pumping by adjusting the ground-state decoherence rate. Enhanced optical pumping through the manipulation of the magnetic field is quite important and is of great interest in the field of quantum technology.