Abstract
The component of orbital angular momentum (OAM) in the propagation direction is one of the fundamental quantities of an electron wave function that describes its rotational symmetry and spatial chirality. Here, we demonstrate experimentally an electrostatic sorter that can be used to analyze the OAM states of electron beams in a transmission electron microscope. The device achieves postselection or sorting of OAM states after electron-material interactions, thereby allowing the study of new material properties such as the magnetic states of atoms. The required electron-optical configuration is achieved by using microelectromechanical systems technology and focused ion beam milling to control the electron phase electrostatically with a lateral resolution of 50nm. An OAM resolution of 1.5ℏ is realized in tests on controlled electron vortex beams, with the perspective of reaching an optimal OAM resolution of 1ℏ in the near future.
Highlights
The component of orbital angular momentum (OAM) in the propagation direction is one of the fundamental quantities of an electron wave function that describes its rotational symmetry and spatial chirality
An OAM sorter provides decomposition of all OAM channels at the same time by making use of a conformal mapping from Cartesian to log-polar coordinates. Such a coordinate transformation permits radial and azimuthal degrees of freedom to be decoupled. Since it corresponds to a unitary change of basis, all of the components of the electron beam that have a chosen OAM value are propagated into a single region of space with virtually no loss and with superior efficiency to the use of a pitchfork hologram [50], despite the simplicity of the latter concept
We present preliminary results that demonstrate its successful operation, including the recording of OAM spectra in a transmission electron microscope
Summary
The component of orbital angular momentum (OAM) in the propagation direction is one of the fundamental quantities of an electron wave function that describes its rotational symmetry and spatial chirality. Experimental Demonstration of an Electrostatic Orbital Angular Momentum Sorter for Electron Beams
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