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Chinese Journal of Lasers

A Simple Demonstration of Optical Pumping Effect

Wang Yu-zhu

Published Jan 1, 2004• 0 citations
OpenAlex

Abstract

Two sets of laser system are used, one as a probing beam, the other as an optical pumping beam, to analyze the population distribution of the magnetic sublevel. By scanning the frequency of the optical pumping beam at different frequency, the absorption spectrum is got, from which the population variation of some sublevel can be deduced.

Related papers

Anomalies in the shape of atomic resonant absorption lines under conditions of strong optical pumping of hyperfine structure components of the ground state

А. И. Пархоменко, S.P. Pod'yachev, Timofei Privalov +1 more

The ground electronic state of even such simple atoms as those of alkali elements has the set of sublevels. These sublevels are hyperfine (HF) components and magnetic sublevels. The collisions with particles of nonmagnetic buffer gas or even with walls (when walls have proper coating) do not mix practically the populations of ground state HF sublevels, if the orbital moment of electrons in the ground state is equal to zero. Due to this reason these sublevels may be extremely long lived. Because of this, for instance, the so-called effects of optical orientation and optical pumping are apparent in atoms of alkali metals. The radiation can pump practically all the atoms (with which there is effective interaction) to a single HF component. In a situation in which optical pumping is a minor effect, the monochromatic absorption line consists of separate lines corresponding to intra-atomic transitions. The optical pumping is not significant, for example, if the radiation intensity is so low that now pumping between HF sublevels occurs in the time it takes the atom to traverse the light beam. Under the conditions of optical pumping and when other nonlinear effects are present, the absorption line profile can undergo considerable alteration. Many theoretical and experimental investigations have been done in the laser spectroscopy of resonant transitions of atoms (atoms of alkali metals) under the conditions of optical pumping within ground state HF structure. A characteristic feature of all such investigations is the velocity-selective excitation of absorbing atoms. Also, as a rule, the value of HF splitting is not very big in comparison to Doppler broadening in these experiments. Under such conditions, the absorption spectra consists of Doppler- broadened lines with nonlinear resonances, which emerge when two fields of different frequencies or different propagation directions are employed. When only one monochromatic traveling wave is employed, optical pumping leads to formation of a single smooth absorption line occupying a position between the resonant transitions frequencies associated with HF components. As HF splitting grows, the line profile remains smooth, its width is approximately equal to the size of the HF splitting. The strength of the optical pumping from one ground state HF component to another is greater for greater HF splitting in comparison to the Doppler width. In this regard, Cs and Rb are the most typical of the alkali atoms (the HF splitting exceeds the Doppler width by a factor close to 20). This is the qualitative picture of the absorption line profile (particularly for a monochromatic radiation) under the conditions of optical pumping between the HF sublevels of the electronic ground state, this qualitative picture had formed by now.

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Investigation of Optical Pumping in Cesium Atoms with a Radio-Frequency Field, Using Liouville Equation

Hossein Davoodi Yeganeh, Zahra Shaterzadeh‐Yazdi

Optical pumping is a technique for engineering atomic-sublevel population of desired atoms. We investigate the population evolution of Cesium atoms by employing Liouville equation. For this purpose, we apply a circularly polarized light at a frequency suitable for electronic transition from ground states to excited states and calculate the relaxation rate, repopulation, and population evolution of the Cesium Zeeman sublevels. For engineering the sublevel population after optical pumping, we employ a radiofrequency (RF) field and consider the effect of RF field in Liouville equation. With this approach, we are able to prepare desired distribution of the population in the atomic sublevels with high efficiency, which can be employed in different optical experiments.

arXiv:2304.00301•Apr 1, 2023•0 citations
The ground electronic state of even such simple atoms as those of alkali elements has the set of sublevels. These sublevels are hyperfine (HF) components and magnetic sublevels. The collisions with particles of nonmagnetic buffer gas or even with walls (when walls have proper coating) do not mix practically the populations of ground state HF sublevels, if the orbital moment of electrons in the ground state is equal to zero. Due to this reason these sublevels may be extremely long lived. Because of this, for instance, the so-called effects of optical orientation and optical pumping are apparent in atoms of alkali metals. The radiation can pump practically all the atoms (with which there is effective interaction) to a single HF component. In a situation in which optical pumping is a minor effect, the monochromatic absorption line consists of separate lines corresponding to intra-atomic transitions. The optical pumping is not significant, for example, if the radiation intensity is so low that now pumping between HF sublevels occurs in the time it takes the atom to traverse the light beam. Under the conditions of optical pumping and when other nonlinear effects are present, the absorption line profile can undergo considerable alteration. Many theoretical and experimental investigations have been done in the laser spectroscopy of resonant transitions of atoms (atoms of alkali metals) under the conditions of optical pumping within ground state HF structure. A characteristic feature of all such investigations is the velocity-selective excitation of absorbing atoms. Also, as a rule, the value of HF splitting is not very big in comparison to Doppler broadening in these experiments. Under such conditions, the absorption spectra consists of Doppler- broadened lines with nonlinear resonances, which emerge when two fields of different frequencies or different propagation directions are employed. When only one monochromatic traveling wave is employed, optical pumping leads to formation of a single smooth absorption line occupying a position between the resonant transitions frequencies associated with HF components. As HF splitting grows, the line profile remains smooth, its width is approximately equal to the size of the HF splitting. The strength of the optical pumping from one ground state HF component to another is greater for greater HF splitting in comparison to the Doppler width. In this regard, Cs and Rb are the most typical of the alkali atoms (the HF splitting exceeds the Doppler width by a factor close to 20). This is the qualitative picture of the absorption line profile (particularly for a monochromatic radiation) under the conditions of optical pumping between the HF sublevels of the electronic ground state, this qualitative picture had formed by now.
In this study, we examined the effect of pump laser beam diameter on saturated absorption spectra. The rate equations describing the dynamics of the population of each sublevel were solved and the time evolution of the signals was obtained theoretically. With the exception of some signals, the experimental results showed good agreement with the calculated results, which were analyzed using the calculation based on rate equations. Furthermore, the beam diameter dependence of the spectra was examined for several pump beam intensities, and the results matched the calculated results.
We have observed a sudden reversal in the direction of population transfer between nearly degenerate Zeeman sublevels during optical pumping of the cesium 6S1/2{\mathit{S}}_{1/2}S1/2​(F=4)\ensuremath{\rightarrow}6P3/2{\mathit{P}}_{3/2}P3/2​(F'=5) cycling transition. As a result of the reversal, the number of atoms in an atomic beam, with quantum numbers 6S1/2{\mathit{S}}_{1/2}S1/2​ (F=4; mF{\mathrm{m}}_{\mathit{F}}mF​=-4), is a function of laser frequency and has a sharp dispersive shape. A rate-equation model indicates that similar dispersive shapes for the population can be expected in the optical pumping of any nondegenerate system with more than two levels, if the level spacing is much smaller than the laser linewidth.
A theoretical analysis of the relative intensities of the Doppler-free signals in saturation spectroscopy, velocity selective optical pumping (VSOP) spectroscopy, polarization spectroscopy and a mixing of saturation and polarization spectroscopies is presented using the approximation of a single cycle of optical pumping in a four-level system. An optical pumping process in the Zeeman sublevels is taken into account owing to the important role of spontaneous emission even if the sublevels are degenerate. Arbitrary polarization combinations are considered for pump and probe beams. The similarities and differences between three kinds of spectroscopy are made clear. Both circular and linear optical anisotropies induced by the pump beam are considered in this theoretical calculation. The magnitude and sign of Doppler-free resonances in each spectroscopy are quite different owing to the polarizations of the pump and probe beams. The four-level system is important as a three-level approximation. The results obtained from the four-level optical pumping theory are in good agreement with experimental reports.
New sub-Doppler resonances at central frequencies of atomic (molecular) transitions that appear in the spectrum of absorption of the probe optical radiation under the influence of optical pumping propagating in the orthogonal direction through a relatively narrow area of a cylindrical cell containing dilute gas medium are discovered and analyzed. These resonances are induced by specific optical pumping of atoms as they fly freely from the inner cell surface through the pumped region toward the probe optical beam. The obtained mathematical relations are used to investigate the dependence of the discussed resonances on the intensity and spatial distribution of the localized optical pumping. The proposed method could allow reducing the Doppler broadening of the detected spectral lines by the factor equal to the ratio of the effective width of the narrow pumped region to the cell radius. The obtained results may find application in high-resolution spectroscopy of atoms (molecules), as well as for laser-frequency stabilization by using the discovered sub- Doppler resonances.
Optical pumping is a technique for engineering atomic-sublevel population of desired atoms. We investigate the population evolution of Cesium atoms by employing Liouville equation. For this purpose, we apply a circularly polarized light at a frequency suitable for electronic transition from ground states to excited states and calculate the relaxation rate, repopulation, and population evolution of the Cesium Zeeman sublevels. For engineering the sublevel population after optical pumping, we employ a radiofrequency (RF) field and consider the effect of RF field in Liouville equation. With this approach, we are able to prepare desired distribution of the population in the atomic sublevels with high efficiency, which can be employed in different optical experiments.