Optical Pumping Experiments Research Articles

Acoustic resonance in an optically pumped Rb vapour

An optical pumping experiment is described where the pumped rubidium atoms were submitted to an acoustic vibration. A modulation in the transmitted light was observed when the acoustic frequency matched the Larmor precession frequency. An interpretation of the experimental observations could not be found.

Control of chemical equilibrium through optical pumping

Kastler has shown that the equilibrium rate between alkali dimers and atoms can be changed by optical orientation of the unpaired valence electron of the atom. Optical pumping experiments performed in Pisa which prove Kastler considerations are here recalled.

THE MICROWAVE-RADIO FREQUENCY WAVE MULTI-QUANTUM TRANSITION IN OPTICAL PUMPING EXPERIMENT

In the optical pumping experiment for 87Rb gas cell, when the microwave and radio frequency wave are applied simultaneously, the optically detected resonance signals of microwave-radio frequency wave multi-quantum transition are observed.

Optogalvanic detection of optical pumping

Reports the optogalvanic detection of observables induced by optical pumping in metastable states of neon. As with optical methods signals are obtained which are related to electronic and nuclear orientation or alignment. Many optical pumping experiments may thus be performed using optogalvanic techniques, including the Hanle effect and 'velocity selective optical pumping' described. Different mechanisms are discussed from which optogalvanic signals related to non-scalar observables may originate. Profiles obtained from frequency sweeps of two polarisation-modulated counterpropagating pump beams indicate the dominant mechanism is a second-order pumping effect which induces a modulated depletion of the metastable state. No effect has been observed arising from a variation of the Penning collision cross section when the two metastable colliding atoms are oriented. The analogy between signals produced by optogalvanic and optical methods are pointed out.

Alignment and orientation of the hyperfine levels of a laser excited Na-atom beam

Excitation, orientation and alignment of a Na atomic beam is studied in a laser optical pumping experiment for the $$3^2 S_{1/2} \bar F = 2 \leftrightarrow 3^2 P_{3/2} F = 3$$ transition. For practical application in collision experiments with laser excited atom beams, we relate the observable parameters to several alternative descriptions by multipole moments, and discuss the experimental geometries most suitable for their determination. The dependences on laser power, atom beam density, small magnetic fields and spatial profiles are measured. They can be understood by simple rate equation models.

Evidence for anI=1 isomeric state in96Rb

Aβ-RADOP (β-Radiation Detected Optical Pumping) experiment on the short lived (T1/2=203 ms)96Rb isotope has been performed at the on line mass separator for fission produced alkali isotopes at the TRIGA reactor in Mainz. Irradiation of r.f. onto the polarized sample to induce Zeeman transitions resulted in two signals for nuclear spinsI=2 andI=1. The previously undetermined component withI=1 is interpreted as evidence for an isomeric state in96Rb.

Double-resonance and optical-pumping experiments on electromagnetically confined, laser-cooled ions

Experiments illustrating advantages and unique features of double-resonance and optical pumping on electromagnetically confined, laser-cooled ions are discussed. In certain cases, scattered light from the cooling transition can be used as a monitor in double-resonance experiments to give nearly 100% detection efficiency. Nonradiative relaxation rates are extremely small for stored ions, permitting nearly complete optical pumping, even in extremely weak pumping schemes.

K-K+charge-exchange cross section

A charge-exchange optical-pumping experiment to measure the K+K+ charge-exchange cross section in a He buffer gas has been performed. K+ ions are polarised by charge-exchange collisions with optically pumped K atoms. The value of the charge-exchange cross section sigma ce(K+-K) at thermal energy is measured to be (5.4+or-0.8)*10-14 cm2.

The role of the Pauli principle in metastability exchange collisions

In optical pumping experiments, metastability exchange collisions are used to transfer orientation, alignment, ... between different atomic levels. This article studies the effect of such collisions on the atom internal variables density operator by a method used in a previous publication for spin exchange collisions. The calculations are valid when the nuclei of the two atoms are distinguishable as well as when they are identical particles, which allows a detailed discussion of nuclear identity effects (apparent magnetic field, etc...). Two cases are successively studied : no depolarization of the electronic angular momentum (He*-He collisions) and partial depolarization (Ne*-Ne collisions for example). The nuclear identity effects should be observable in low temperature optical pumping experiments with noble gases. In an Appendix, another particle identity effect is studied, which can be observed in atomic beam experiments : during the collision of two 3He atoms, both in the ground state, the spin state of the atoms scattered in a particular direction can be changed by nuclear indistinguishability effects.

Optical pumping of metastable5S oxygen

An optical pumping experiment on the metastable 5S state of atomic oxygen is reported. Metastable atoms were excited by a discharge in a low-pressure mixture of gaseous oxygen and helium. Both a discharge lamp and a CW dye laser at lambda =7773AA were successively used as optical pumping sources. The extrapolated magnetic resonance linewidth is practically equal to the radiative natural linewidth of 0.6 mG ( tau approximately=0.18 ms).

Vanishing electric dipole transition moment

We have discovered an interference which results in the vanishing of some electric dipole transition amplitudes. A transition-matrix element $T$ between certain $S$ and $P$ sublevels with the same value of ${M}_{F}$ vanishes when an applied magnetic field satisfies ${X}_{s}+{X}_{p}=\ensuremath{-}2{M}_{F}$, where $X={\ensuremath{\mu}}_{B}{g}_{J}\frac{B}{A}$, and $A$ is the hfs constant. There must be an avoided crossing between the two states of the same ${M}_{F}$ which can only occur when one of the hyperfine manifolds has an inverted Zeeman effect. These conditions imply ${M}_{F}<0$ and $I>J$. We observed the vanishing of $T$ in $^{23}\mathrm{Na}$ for one of the $\ensuremath{\Delta}{M}_{F}=0$ optical transitions of the $3{S}_{\frac{1}{2}}(F=1)\ensuremath{\rightarrow}3{P}_{\frac{1}{2}}(F=1)$ manifold. Absorption of cw laser light was monitored by observing total fluorescence perpendicular to both the atomic and laser beams, and absorption vanished near an applied field of 155 G. $T$ vanishes for a large number of cases including rf and microwave frequencies and is a rather general consequence of angular momentum selection rules and perturbation theory. This phenomenon may have application in optical pumping, Lamb-shift measurements, and atomic weak neutral-current experiments.

Temperature dependence of Cs-Cs+charge-exchange cross sections

A charge-exchange optical-pumping experiment to study the temperature dependence of the Cs-Cs+ charge-exchange cross section sigma has been performed. Cs+ ions are polarised by resonant charge-exchange collisions with optically pumped Cs atoms. The Cs+ ion resonance linewidths are measured over the temperature range 20-26 degrees C. They are used to study the charge-exchange cross section as a function of temperature. The cross section sigma (Cs+ to Cs) varies inversely as the square root of the temperature. The charge-exchange cross section sigma (Cs+ to Cs) has also been re-measured and found to be (6.6+or-0.5)*10-14 cm2, in good agreement with theoretical calculations.

Low field electron-nuclear spin coupling in gallium arsenide under optical pumping conditions

In a semiconductor, absorption of circularly polarized light (optical pumping) leads to spin-oriented photoelectrons. In this situation, the nuclei of the crystal are dynamically polarized through their hyperfine interaction with the electronic spins. Consequently the electrons experience a hyperfine magnetic field due to the oriented nuclei which may reach several kilogauss. When this large nuclear field is driven obliquely with respect to the direction of the exciting light, the precession of the electronic spins around the nuclear field leads to a decrease of the electronic polarization along the light excitation: it is a nuclear Hanle effect. This work is an experimental and theoretical study of these effects in weak external magnetic fields, of the order of the local field which characterizes the nuclear spin-spin interactions (a few gauss). Large nuclear fields are obtained at 77\ifmmode^\circ\else\textdegree\fi{}K in strongly doped and compensated $p$-type GaAs samples. We present a model which includes the different effects of the hyperfine coupling when there is a nuclear spin temperature among all the nuclei of the sample: Dynamic polarization, nuclear field, but also, existence of an electronic field acting on the nuclei. We show that a small external field is able to drive the large nuclear field acting on the electrons; consequently the electronic polarization is very sensitive to external fields which are too small to have a direct effect on the electronic spin motion. We study experimentally the variation of the electronic polarization with the direction and magnitude of a small external magnetic field, by measuring the circular polarization of the luminescence light. The experimental results are in quantitative agreement with the theoretical predictions. The usual Hanle Lorentzian depolarization curve is strongly modified in low fields and $W$-like singularities appear around zero field. The experimental values of the average electronic and nuclear fields are in reasonable agreement with theoretical evaluations. These nuclear effects may strongly alter the measurement of the Hanle linewidth in standard optical pumping experiments.

Determination of g-factor Ratios for Cs+ Ions and Cs Atoms

A charge-exchange optical pumping experiment to measure the nuclear g factor of 133Cs+ ions in a He buffer gas is reported. Cs+ ions are polarized by charge-exchange collisons with optically pumped Cs atoms. The NMR frequency of 133Cs+ ions along with the Zeeman transition frequency of 133Cs are measured in a magnetic field ∼ 600 G. This gives the ratio of the nuclear g factor of the 133Cs+ ion to the electronic g factor in the ground electronic state of free 133Cs. The result is gI(133Cs+)/gJ(133Cs)=-1.9917235(30). Using this value and results of other researchers yield gI(133Cs+)/gI(133Cs)=0.9999917(21) as the ratio of the nuclear g factor of the Cs ions to that of the free Cs atoms, [σ(Cs+)-σ(Cs)]=7.7(2.0) × 10-6 the difference in the diamagnetic shielding constants of the free atoms and ions. Finally, the value for the shielded Cs+ nuclear moment in units of the Bohr magneton is found to be gI(133Cs+)=3.988511(21) × 10-4.

Effect of diffraction on the measurement of gain in optically pumped materials

Maxwell's equations are solved for the propagation of light in an inhomogeneously excited material. For a particular form of the inhomogeneity, a closed form solution is found which shows that the optical gain measured by optical pumping experiments will be less than the “intrinsic” gain which would be observed in a homogeneously excited material.

The Mechanism of Frequency Shifts in New Coherence Resonances

By means of the dressed atom concept examined theoretically by Cohen-Tannoudji and Haroche, the misalignment effects of an oscillating rf-field in optical-rf double resonances are investigated. We present a fully quantum mechanical calculation of higher-order effects in the frequency shifts of new coherence resonance for the general case that a spin-1/2 atom interacts with the oscillating rf-field in optical-pumping. It is analytically shown that the new type resonances can occur even by taking account of higher-order effects in the perturbation theory for the oscillating rf-field whose direction makes a special angle from that of a static field, and that the direction of the shift of the resonance field is not along that of the static field but perpendicular to that of the oscillating field. Theoretical results are compared with optical-pumping experiments of cesium vapor.

Laser Stark measurements on OCS including the observation of zero-field-forbidden Δ J = 0, ±2 transitions

Laser Stark measurements have been made on the 02 0000 00 and 03 1001 10 vibrational transitions of 16O 12C 32S, 16O 12C 34S, and 18O 12C 32S, and on the 03 1001 10 transition of 16O 13C 32S, using a CO 2 laser. In addition to providing dipole moment information for excited vibrational states, these measurements give vibrational band centers accurate to several megahertz. To aid in optical pumping experiments, several near coincidences between CO 2 laser transitions and OCS absorption lines are discussed. Electric-field-allowed Δ J = 0 transitions are observed for the 2 ν 2 band of 16O 12C 32S and 16O 12C 34S, as well as Δ J = 2 transitions for the same band of 18O 12C 32S.

Photodecomposition in POPOP dye vapor lasers

Experimental evidence is presented which shows that the premature termination of dye vapor laser gain observed in optical pumping experiments is due to photodecomposition. Addition of up to 4 atm of buffer gases was found to have little effect.

Zero-field hyperfine structure measurements of the metastable states 3d 2 4s 4 F 3/2, 9/2 of45Sc using laser-fluorescence atomic-beam-magnetic-resonance technique

In an atomic beam experiment we measured the hyperfine structure (hfs) of the metastable states 3d 2 4s 4 F 3/2,9/2 of Scandium, which were populated by electron impact. A single mode cw dye laser was used to create a population difference between neighbouring hfs states by optical pumping. Rf transitions between these states, equalizing the population numbers, could then be detected by repeating the optical pumping experiment and looking for the laser induced fluorescent light. The following constants of the magnetic dipole and electric quadrupole interactions have been obtained by this method:A 3/2=−158.513(3)MHzB 3/2=−5.19(2)MHzA 9/2=285.967(9)MHzB 9/2=−15.46(70)MHz From these constants and the corresponding values forJ=5/2, 7/2, as measured by [1], the following parameters can be calculated: 〈r −3〉 01 =0.911(4)a 0 −3 〈r −3〉 12 =2.395 (62)a 0 −3 and:α=〈r −3〉 01 /〈r −3〉 12 =0.38(1).

Power shifts of multiphoton transitions in a spin1/2system

Energies of the coupled system of a spin 1/2 atom and a strongly oscillating RF field with an arbitrary direction are numerically calculated, and the size and direction of the power shifts of the multiphonon transitions are obtained. The intensity and shape of the multiphoton resonances appearing in optical pumping experiments are also calculated with the semiclassical theory. An optical pumping experiment is performed with caesium vapour to check the validity of the theoretical results, and good agreement is found.