Dual-frequency optical pumping for spin-polarizing a lithium atomic beam

A lithium-6 atomic beam is spin-polarized by means of optical pumping with a single-mode dye laser operating on the resonance transition. Simultaneous pumping of both hyperfine substates is achieved by frequency-splitting the laser light with an acousto-optic modulator. A polarization dependent signal, obtained by probing the optical activity of the beam with linearly polarized light, is utilized in a microprocessor-controlled laser stabilization scheme. The polarization is analyzed with a sextupole magnet and its overall value is 0.70 for an intensity of 1×10¹⁴ atms s⁻¹. By reversing the sense of circular polarization of the pumping light the atomic beam polarization is easily reversed in direction.     

Optical pumping of cesium atoms with second resonance light

We report the first successful optical pumping of cesium atoms to a state of high spin polarization with a CW dye laser tuned to the D₁ second resonance line (4593 Å) of the cesium atom. Results of spin polarization versus laser power measurements for cells containing high-density cesium vapors (10¹³–10¹⁵ cm^-3) plus mixtures of nitrogen (10–200 torr) and helium (≈1 atmosphere) gases are presented. These experiments have revealed unexpected limits to the spin polarization of dense alkali vapors.     

Spin dependency of optical feeding into the Ē(2E) metastable doublet of ruby

An analysis has been made of spin polarization memory in the ē(²E) metastable doublet of Cr³⁺ in Al₂O₃ upon broadband optical pumping with unpolarized light. Coefficients describing the relative feeding rates of all four ⁴A₂ ground-state levels into the two ē(²E) levels have been obtained. The optical pumping cycle appears to contain a component with Δm_S=±2.     

Interrelationship between the polarization moments of different parity upon optical pumping of atoms under magnetic resonance conditions: III. Comparison of theory with experiment

The optical pumping of Cs atoms with light of the D ₁ line under magnetic resonance conditions is numerically calculated. This calculation is done to check the suggestion that an unexpectedly strong influence of the polarization of the pumping light on the resonance signals of transverse alignment, which we observed experimentally, is caused by the coupling between orientation and alignment by means of the magnetic field and/or the pumping light. This suggestion has been confirmed: upon circularly polarized pumping, the shape of the signal line of transverse alignment proved to be similar, as well as in the experiment, to the shape of the signal line of transverse orientation and was sharply different from the shape of the line of alignment observed upon linearly polarized pumping. For metastable 2³ S ₁ ⁴He atoms, in accordance with the experimental data, the calculated shape of the signal line of transverse alignment is found to be independent of the polarization of the pumping light. The calculations also confirm the possibility of a reverse effect: the influence of alignment on orientation, which manifests itself in the occurrence of orientation upon pumping with unpolarized light under magnetic resonance conditions. For Cs atoms exposed to a field of ～0.6 Oe, the largest contribution to this effect is yielded by the field coupling of orientation and alignment, whereas, for metastable 2³ S ₁ ⁴He atoms, the largest contribution is made by the light coupling of these polarization moments.     

Influence of atomic alignment on crossover signals in saturation spectroscopy

The crossover resonance between the atomic transitions² S _1/2(F=2)→² P _1/2(F′=1, 2), observed in the saturation spectrum of sodium, was found to be sensitive to the atomic orientation of the ground state, produced by velocity selective optical pumping. For zero magnetic field and the same linear polarization of saturating and probing beam, a negative signal was recorded for the crossover, corresponding to an increase in absorption of the probing beam. Application of a sufficiently strong magnetic field perpendicular to the polarization vector causes the destruction of the alignment, leading to a change in sign for the crossover intensity, i.e., to an enhanced transmission of the probing beam. It was shown experimentally that an increase in the atomic transit time has the same effect. Using optical pumping theory all qualitative features could be accounted for.     

Saturation spectroscopy of hydrogen 1-011-011-01lines with a multi-mode cw dye laser

With an intense, broadband multi-mode cw dye laser collisional studies of H_α fine-structure resonances with saturated absorption are extended to He buffer gas pressures larger than 30 mbar (0°C). The broadening and shift of the two prominent H_α(2P?3D) transitions are measured in a (He+4% H) gas discharge. The absolute magnitude and the differences in the width of the lines are explained theoretically by different inelastic fine-structure transfer cross sections which can also be deduced from the pressure effect data. Nuclear polarization of hydrogen atoms by H_α optical pumping and polarization transfer to the H(1S) ground state via Ly-α decay and further applications of the multimode laser are discussed.     

Configuration and Performance of a Mobile 129Xe Polarizer

A stand-alone, self-contained and transportable system for the polarization of ¹²⁹Xe by spin exchange optical pumping with Rb is described. This mobile polarizer may be operated in batch or continuous flow modes with medium amounts of hyperpolarized ¹²⁹Xe for spectroscopic or small animal applications. A key element is an online nuclear magnetic resonance module which facilitates continuous monitoring of polarization generation in the pumping cell as well as the calculation of the absolute ¹²⁹Xe polarization. The performance of the polarizer with respect to the crucial parameters temperature, xenon and nitrogen partial pressures, and the total gas flow is discussed. In batch mode the highest ¹²⁹Xe polarization of P_Xe = 40 % was achieved using 0.1 mbar xenon partial pressure. For a xenon flow of 6.5 and 26 mln/min, P _Xe = 25 % and P _Xe = 13 % were reached, respectively. The mobile polarizer may be a practical and efficient means to make the applicability of hyperpolarized ¹²⁹Xe more widespread.     

Polarization spectroscopy of Rb and Cs

Theoretical calculation of ⁸⁵Rb and ¹³³Cs D₁ signals in polarization spectroscopy is presented by using the method of velocity-selective optical pumping in a four-level system. Since good agreement between theory and experiment has been found in Na D₁ polarized signals, the theoretical calculation can be also applied to Rb and Cs D₁ lines. Rb and Cs atoms have higher total angular momentum F in the hyperfine structures than Na atom and then the calculation is more complicated. The relative signal intensities in polarization spectroscopy are compared with those in saturation spectroscopy.     

Interrelationship between the polarization moments of different parity upon optical pumping of atoms under the magnetic resonance conditions: I. Experiment on the <Superscript>133</Superscript>Cs and <Superscript>4</Superscript>He atoms

In an experiment with an optical pumping of ¹³³Cs atoms in the 6² S _1/2 ground state, the line shape of the D ^2f magnetic resonance signal for the transverse alignment component oscillating at a double frequency f of a radio-frequency (RF) magnetic field is found to strongly depend on the polarization of pumping radiation. On passage from a linearly polarized pumping light to a circularly polarized (CP) light with a sufficiently strong RF field the ordinary three-peak line with the highest central peak transforms into a two-peak line with a minimum at the center, so that the D ^2f signal line resembles the M ^f signal line of a transverse orientation oscillating at the RF field frequency f. This suggests that the orientation (the first-rank polarization moment (PM)) arising upon CP pumping affects the alignment (the second-rank PM); i.e., the PMs of Cs atoms with different parities of their ranks become coupled. No influence of the polarization of a pumping radiation on the line shape of the D ^2f signal is observed in a similar experiment with the ⁴He atoms in the 2³ S ₁ metastable state.     

Exciton-exciton annihilation in TbPO4

A pulsed tuneable dye laser has been used to create high densities of excitons in TbPO₄ by resonant optical pumping into the ⁵D₄ Manifold. Non-exponential decay of the fluorescent radiation from ⁵D₄ is ascribed to exciton-exciton annihilation whose rate γn, is proportional to the exciton density n, with γ = 5 × 10^-15 cm³sec^-1. Anti-Stokes' radiation which is emitted by the annihilation products is also observed.     

Lifetime measurement of the (5d6p)3D3 state of barium by dye-laser spectroscopy

We have measured the radiative lifetime of the (5d6p)³D₃ state of barium by Hanle effect. This state was populated by cw dye laser excitation of an atomic beam of Ba in the metastable (5d6s)³D₃ state. The metastable state was populated by a dc discharge. With dye laser excitation, the shape of the Hanle effect curve is strongly modified due to optical pumping of the metastable state. A brief discussion of the expected and observed signal shapes is given. The radiative lifetime of the (5d6p)³D₃ state is measured to be τ = 10.2 ± 1.5 ns.     

Spin polarization in a freely evolving sample of cold atoms

We have implemented and optimized a technique of spin polarization by optical pumping in a caesium atomic fountain, gaining a nearly fivefold increase in the useful cold atom signal in detection. This allows an improvement of the fountain clock stability without compromising its accuracy. We present a detailed study of optical pumping in a freely evolving cloud of cold caesium atoms: we have investigated theoretically and experimentally the dynamics of the pumping process and the associated heating due to random photon scattering. The heating limits the potential gain in the fountain signal due to an additional cloud expansion. A high degree of spin polarization was achieved with accumulation of up to 97 % of the population in a single magnetic (m _F  = 0) sublevel of the ground state. Factors affecting the achievable spin polarizations, such as the purity of the pumping light polarization and the shadowing effect in the cloud, were considered. This technique may also be used in atom interferometers and for other alkali metal systems.     

Spin exchange polarization and measurement of the hyperfine splitting of short-lived8Li

Free⁸Li (T _1/2=0.84 sec) atoms were polarized by spin exchange with optically pumped rubidium vapour. The⁸Li nuclei were produced by the reaction⁷Li(d, p)⁸Li in a thin LiF target. They recoiled into helium which was used as a buffer gas for optical pumping as well. Nuclear polarization up to 2% was detected by β-decay asymmetry. Rf transitions between hfs levels of the atomic ground state yielded the hfs separation ΔW=382.543(7) MHz. The nuclear spin assignmentI=2 was confirmed.     

Production of a highly polarized sodium atomic beam

Two experimental techniques for preparing atoms in selected states were combined in order to obtain a highly polarized sodium beam: Firstly state selection by an inhomogeneous magnetic field and secondly optical pumping with laser light. This results in a dominating population of the 3s ² S _1/2 ground state levelF=2M _F=+2 (or alternativelyF=2M _F=−2) corresponding to high electron as well as nuclear spin polarization. Polarization values of 0.85±0.05 were easily obtained. The sign of the polarization can be reversed by changing the light polarization. The method can also be applied to other atoms. In addition, it is demonstrated that the optical pumping process allows a determination of the spin-selectivity of hexapole magnets.     

Die Bestimmung der Spin-Polarisation aus Transparenz-Änderungen beim Optischen Pumpen mit der Natrium-D1-Linie

A Dehmelt type experiment is performed in which sodium vapor and argon as a buffer are employed. The pumping radiation consists of the circularly polarizedD ₁ line. Since the strongly absorbing magnetic sublevels are depopulated, the vapor becomes more transparent to the pumping radiation with growing polarization. The transparency of the vapor is measured with and without optical pumping as a function of the sodium vapor density. The degree of polarization is determined in simulating the increase in transparency due to polarization by decreasing the sodium vapor density of the unpumped sample. This method requires the knowledge of the exact sodium vapor density in the temperature range of interest (100 to 200° C). The determination of the degree of polarization is based on the assumption, that the atomic absorption cross sectionQ, which depends on the degree of polarizationP and the frequency of lightν, can be written in the formQ(P,ν)=A(P) · B(ν), whereA(P) is a linear function ofP, whileB (ν) must not be changed by optical pumping. As will be shown in a following paper, the degree of polarization determined under this assumptions, describes in good approximation the polarization of the sodium valence electrons.     

Kontinuierlicher Absorptionsquerschnitt von Argon im Bogenplasma

Optical pumping on Cs¹³³ atoms was performed by means of a new transmission technique. The cesium vapor was pumped towards equilibrium by an intensive circulary polarizedD ₁ orD ₂ light beam. A weakD ₁ detecting beam was polarized alternately σ⁺, σ^? and allowed one to measure continuously amount and sign of the absorption difference between σ⁺ and σ^? light. The measured signals are proportional to the electron spin polarization. The new technique was used to investigate the influence of Cs buffer gas collisions on the pumping cycle and to measure the influence of radio frequency induced Zeeman transitions on the ground state polarization. In addition the variation of magnetic field and of pumping light intensity and polarization was studied. Some measurements demonstrate the high sensitivity of the applied method. The obtained qualitative results are discussed and further experiments are proposed.     

Quadrupole interaction of8Li and9Li in LiNbO3 and the quadrupole moment of9Li

The quadrupole interaction of nuclear spin polarized⁸Li (I=2) and⁹Li (I=3/2) in LiNbO₃ has been studied at room temperature. The polarization was achieved by optical pumping of a fast atomic beam with circularly polarized laser light. The atoms were implanted into a hexagonal LiNbO₃ single crystal and the quadrupole splitting ofβ-NMR spectra was measured. A ratio of ¦Q(⁹Li)/Q(⁸Li)¦=0.88(4) for the nuclear quadrupole moments was deduced, yielding a new value of ¦Q(⁹Li)¦=25.3 (9) mb for the quadrupole moment of⁹Li.     

Cyclic interaction of Na atoms with circularly polarized laser radiation

Cyclic interaction of Na atoms with laser radiation is under consideration. In the experiment cyclic interaction was conducted through preliminary optical pumping of the atom into the ground state F = 2, M_F = 2 by a single-mode cw dye laser. The results of optical orientation of Na atom and cyclic interaction under different conditions of atomic excitation are presented. Possible applications of cyclic interaction of atom with radiation for detection and cooling of atoms is under discussion.     

Z-scan and optical limiting properties of Hibiscus Sabdariffa dye

The intensity-dependent refractive index n ₂ and the nonlinear susceptibility χ ⁽³⁾ of Hibiscus Sabdariffa dye solutions in the nanosecond regime at 532 nm are reported. More presicely, the variation of n ₂, β, and real and imaginary parts of χ ⁽³⁾ versus the natural dye extract concentration has been carried out by z-scan and optical limiting techniques. The third-order nonlinearity of the Hibiscus Sabdariffa dye solutions was found to be dominated by nonlinear refraction, which leads to strong optical limiting of laser.     

Interrelationship between the polarization moments of different parity upon optical pumping of atoms under magnetic resonance conditions: II. Theory

The mutual coupling between the polarization moments with ranks of different parity is theoretically considered. The manifestation of this mutual coupling has been revealed previously in experiments on magnetic resonance of optically oriented cesium atoms. The two well-known types of the coupling between the polarization moments are considered: the field coupling of these moments that occur due to the breaking of the hyperfine coupling between the electronic and nuclear moments of the alkali atom by the magnetic field and the light coupling of the moments due to the absorption of the pumping light by polarized atoms. The experimentally observed similarity in the shape of resonance signals of alignment and orientation upon circularly polarized pumping can be explained by the fact that, for alkali atoms, the generation of alignment by light at the wavelength of the D ₁ line is of low efficiency. Therefore, alignment arises mainly from orientation by means of either the field or the light coupling of polarization moments. For metastable 2³ S ₁ ⁴He atoms, no influence of the orientation on the alignment was observed because, in these atoms, the field coupling between the polarization moments is absent and the light coupling is not displayed because the generation of alignment by the circularly polarized pumping light is more efficient than the creation of alignment from orientation by means of light coupling of polarization moments.