Compact inline optical electron polarimeter

Pirbhai, Munir; Ryan, D. M.; Richards, Gary J.; Gay, T. J.

doi:10.1063/1.4807745

Cited by 8 publications

(3 citation statements)

References 27 publications

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“…in the range 10 À3 -10 À4 . Note that the efficiency of the optical electron polarimeter based on the measurement of fluorescent polarization in atomic transitions excited by the electrons was estimated to be on the order 10 À10 (Trantham et al, 1996) with further improvement to 10 À8 (Pirbhai et al, 2013).…”

Section: Perspectivesmentioning

confidence: 99%

A new imaging concept in spin polarimetry based on the spin-filter effect

Tereshchenko¹,

Golyashov²,

Rusetsky³

et al. 2021

J Synchrotron Rad

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The concept of an imaging-type 3D spin detector, based on the combination of spin-exchange interactions in the ferromagnetic (FM) film and spin selectivity of the electron–photon conversion effect in a semiconductor heterostructure, is proposed and demonstrated on a model system. This novel multichannel concept is based on the idea of direct transfer of a 2D spin-polarized electron distribution to image cathodoluminescence (CL). The detector is a hybrid structure consisting of a thin magnetic layer deposited on a semiconductor structure allowing measurement of the spatial and polarization-dependent CL intensity from injected spin-polarized free electrons. The idea is to use spin-dependent electron transmission through in-plane magnetized FM film for in-plane spin detection by measuring the CL intensity from recombined electrons transmitted in the semiconductor. For the incoming electrons with out-of-plane spin polarization, the intensity of circularly polarized CL light can be detected from recombined polarized electrons with holes in the semiconductor. In order to demonstrate the ability of the solid-state spin detector in the image-type mode operation, a spin detector prototype was developed, which consists of a compact proximity focused vacuum tube with a spin-polarized electron source [p-GaAs(Cs,O)], a negative electron affinity (NEA) photocathode and the target [semiconductor heterostructure with quantum wells also with NEA]. The injection of polarized low-energy electrons into the target by varying the kinetic energy in the range 0.5–3.0 eV and up to 1.3 keV was studied in image-type mode. The figure of merit as a function of electron kinetic energy and the target temperature is determined. The spin asymmetry of the CL intensity in a ferromagnetic/semiconductor (FM-SC) junction provides a compact optical method for measuring spin polarization of free-electron beams in image-type mode. The FM-SC detector has the potential for realizing multichannel 3D vectorial reconstruction of spin polarization in momentum microscope and angle-resolved photoelectron spectroscopy systems.

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Section: Perspectivesmentioning

confidence: 99%

A new imaging concept in spin polarimetry based on the spin-filter effect

Tereshchenko¹,

Golyashov²,

Rusetsky³

et al. 2021

J Synchrotron Rad

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“…This method has been explored previously at MAMI 122,123 but most recently a program dubbed Accurate Electron Spin Optical Polarimetry (AESOP) is being pursued by the Nebraska group. 124,125 In this effort the goal of the Nebraska group is to measure optical polarization to a statistical accuracy of 0.1% and an overall accuracy of 0.4%. With such accuracy, AESOP opens a new pathway to test systematics of other polarimetry methods, e.g., by accelerating the same Fig.…”

Section: Electron Spin Optical Polarimetrymentioning

confidence: 99%

Precision electron beam polarimetry for next generation nuclear physics experiments

Aulenbacher

Chudakov

Gaskell

et al. 2018

Int. J. Mod. Phys. E

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Polarized electron beams have played an important role in scattering experiments at moderate to high beam energies. Historically, these experiments have been primarily targeted at studying hadronic structure -from the quark contribution to the spin structure of protons and neutrons, to nucleon elastic form factors, as well as contributions to these elastic form factors from (strange) sea quarks. Other experiments have aimed to place constraints on new physics beyond the Standard Model. For most experiments, knowledge of the magnitude of the electron beam polarization has not been a limiting systematic uncertainty, with only moderately precise beam polarimetry requirements. However, a new generation of experiments will require extremely precise measurements of the beam polarization, significantly better than 1%. This paper will review standard electron beam polarimetry techniques and possible future technologies, with an emphasis on the ever-improving precision that is being driven by the requirements of electron scattering experiments.

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“…Here they undergo spin exchange with the oriented Rb before being extracted through a 2-mm-diam aperture that also allows optical-pumping light into the cell. The polarized electrons then traverse a 20-cm differential pumping chamber and enter a helium optical electron polarimeter [9].…”

mentioning

confidence: 99%

Optically pumped spin-exchange polarized-electron source

Pirbhai

2013

Phys. Rev. A

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We describe the operation of a prototype polarized-electron source. Rubidium vapor, contained in a cell, is optically pumped in the presence of a buffer gas. Unpolarized electrons from a tungsten filament are injected into the cell and extracted after undergoing spin exchange with the Rb atoms. We compare the performance of the source when different buffer gases are used. We measure a decrease in electron polarization as their injection energy increases, but find an unexpected regime at higher injection energies yielding increased electron polarization accompanied by a 40-fold increase in current, suggesting the production of slow secondary electrons in the target cell. With ethylene, we have measured electron currents of 4 μA simultaneously with electron polarizations of 24%. This work offers the promise of a simple, benchtop, "turnkey" source of polarized electrons.The use of polarized electrons is widespread in physics, from probing of the spin structure of nucleons and nuclei [1] to studying magnetic domain structure [2] and the spin dependence of atomic collisions [3]. The additional information provided by studies with incident polarized-electron beams comes at a price: The technological demands of polarized-electron sources are severe. The current state-ofthe-art source technology is based on photoemission from negative electron affinity (NEA) strained GaAs photocathodes [4,5]. The modern GaAs source can produce high-current (ß1 mA), high-brightness beams with ࣙ80% polarization. Also, importantly, it is optically reversible; the electron-spin direction can be flipped by reversing the helicity of the light producing photoemission from the GaAs. This enables a relatively straightforward diagnosis of systematic experimental error due to instrumental asymmetries. The biggest drawback of the GaAs source is that it is difficult to operate, particularly with regard to production of the NEA conditions that allow reasonable photocurrents to be extracted. In university labs, the learning curve for reliable graduate student operation of such sources is measured in months (or years); at accelerators, e.g., CEBAF, a dedicated scientific staff maintains and runs these sources. Several attempts to develop the GaAs source into a "blackbox" commercial technology have failed [6].We are currently investigating the interaction of longitudinally polarized electrons, which are chiral, with chiral molecular targets. The observation of handedness-specific scattering provides information about novel molecular collision dynamics [3], as well as possible clues to the mystery of why all naturally occurring DNA has the same handedness [7]. In tabletop experiments with vapor targets, such as ours, destruction of the photocathode's NEA surface conditions by organic and other vacuum contaminants can make GaAs sources unusable or, at best, highly problematic. If a different, user-friendly source of polarized electrons, such as the one we describe here, were widely available, it could enable a broad range of experiments, including those in...

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Compact inline optical electron polarimeter

Cited by 8 publications

References 27 publications

A new imaging concept in spin polarimetry based on the spin-filter effect

A new imaging concept in spin polarimetry based on the spin-filter effect

Precision electron beam polarimetry for next generation nuclear physics experiments

Optically pumped spin-exchange polarized-electron source

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