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Journal of Physics E Scientific Instruments

A spin flipper for reversal of polarisation in a thermal atomic beam

W Schroder, G. Baum

Published Jan 1, 1983• 28 citations
Publisher

Abstract

By using the method of diabatic passage, the authors have developed a spin flipper which allows a rapid and convenient reversal of the atomic spins. The spin flipper was tested with a polarised lithium atomic beam by analysing the atomic beam polarisation with the help of a second spin-flip region and a sextupole magnet. The reversal efficiency was measured to be 0.98 which is in agreement with the calculation. The flipper is especially useful in low-energy electron-atom crossed-beam collision studies. The experimental arrangement used also allows a precise determination of the atomic beam polarisation.

DOI
10.1088/0022-3735/16/1/011

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A spin flipper for thermal atomic beams

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The spin flipper presented here is based on the method of diabatic passage. It allows for a rapid reversal of electronic as well as nuclear polarization of a thermal atomic beam without affecting beam intensity, beam profile, or magnetic fields in the interaction region. The flipper will be useful in spin dependent measurements where instrumental asymmetries and systematic errors have to be kept small. The spin flipper was tested with a polarized lithium beam in an atomic physics experiment and the reversal efficiency was found to by 0.98. The flipper can easily be adapted for other spin‐polarizable atoms, e.g. for a polarized atomic hydrogen beam target.

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Physical Review Letters•Mar 16, 1992•31 citations
By using the method of diabatic passage, the authors have developed a spin flipper which allows a rapid and convenient reversal of the atomic spins. The spin flipper was tested with a polarised lithium atomic beam by analysing the atomic beam polarisation with the help of a second spin-flip region and a sextupole magnet. The reversal efficiency was measured to be 0.98 which is in agreement with the calculation. The flipper is especially useful in low-energy electron-atom crossed-beam collision studies. The experimental arrangement used also allows a precise determination of the atomic beam polarisation.
The spin flipper presented here is based on the method of diabatic passage. It allows for a rapid reversal of electronic as well as nuclear polarization of a thermal atomic beam without affecting beam intensity, beam profile, or magnetic fields in the interaction region. The flipper will be useful in spin dependent measurements where instrumental asymmetries and systematic errors have to be kept small. The spin flipper was tested with a polarized lithium beam in an atomic physics experiment and the reversal efficiency was found to by 0.98. The flipper can easily be adapted for other spin‐polarizable atoms, e.g. for a polarized atomic hydrogen beam target.
An atomic beam of He in the metastable 2 3 S 1 state can be atomic-spin-polarised by Stern-Gerlach selection using a sextupole magnet. The authors report the first measurements of the polarisation obtained by this method. The authors have determined the metastable beam velocity distribution from a time-of-flight measurement. The distribution was found to be in the range of thermal velocities. The selection efficiency of the sextupole magnet was studied using a Stern-Gerlach deflection with an inhomogeneous dipole field. The experimental results give a vector polarisation close to 95%. Thus, the technique can be useful for many applications.
The observation of the 4π symmetry of spinor wave functions was one of the first and highly debated neutron interference experiments. Polarized neutrons have been used to verify the spin-superposition principle on a macroscopic level when the spin in one beam path is inverted with respect to the other one. This results in a spin polarization perpendicular to both initial spins. When a Rabi flipper is used the final spin polarization rotates in this perpendicular plane with the Larmor frequency of the flipper field. Thus, it produces a “frozen” Larmor spin rotation in free space. In this case the spin-flip is associated with an energy (photon) transfer which causes this effect. A magnetic Josephson effect-like situation exists when spin-flippers with slightly different resonance frequencies are used in both beam paths. When such a spin reversal is done in both beam paths a magnetic Josephson effect analog has been realized which shows a remarkably high energy resolution. Multiphoton exchange can be achieved when off-resonance fields are used.
The ground state magnetic sublevel populations of a cesium atomic beam have been measured by laser-induced fluorescence in a 430 G magnetic field. The detected induced fluorescence spectrum is in excellent agreement with calculation. After preparing the beam in the F=4, M=-4 state by optical pumping with diode lasers, this novel detection technique was used to measure a 93% spin polarization of the atomic beam. We have also demonstrated the use of this technique to detect changes in atomic spin after collisions with electrons.
In the past, the Stern–Gerlach experiment has been used as a standard method for analyzing the population of magnetic substates contained in spin-polarized and/or state-selected atomic/molecular beams. However, this experiment is quite demanding due to its low signal intensity and difficulty in beam alignment. The present study shows that the use of a hexapole magnet and a spin flipper, together with the time-of-flight analysis, allows us to conduct an almost equivalent analysis while greatly improving the signal intensity. Applications to the analysis of spin-polarized triplet excited helium and state-selected O2( 3 Σg−) beams are presented.
Recent experiments using polarized electron beams have shown that spin exchange effects for elastic collisions with O2{\mathrm{O}}_{2}O2​ and NO are much smaller than for Na atoms. We report calculated spin-flip differential cross sections for elastic collisions of polarized electrons with O2{\mathrm{O}}_{2}O2​ in agreement with experiment. In general, we can attribute the large variation of the spin-flip differential cross sections to resonances and interference effects. Such features arising from interference, however, may be washed out in the molecular case due to the average over orientations. Calculations with oriented O2{\mathrm{O}}_{2}O2​ molecules show strong exchange effects as for Na.