Description:
University of Oregon Researchers: Benjamin McMorran, Tyler Harvey
Patent: 9,960,008 issued 5/1/2018 (UO-16-22)
Methods and Devices for Measuring Orbital States of Electrons.
Technology Background/Definition of Problem: Orbital angular momentum (OAM), well known and studied in bound electron systems, is a relatively-recently discovered property of free electrons as well (also called electron vortices). Initial work has focused on electron vortex production, dynamics and properties, as well as techniques for preparing electron probe beams possessing angular momentum. A free electron beam scattered from a target, results in a distribution of OAM states that can be thought of as a new kind of spectrum. The OAM distribution in such spectra can provide new kinds of information about the structural chirality and out-of-plane magnetization of the target. In applications such as electron microscopy, spectroscopy, laboratory systems and in synchrotrons, electrons can scatter to many different final OAM states, and the measurement of the final OAM distribution could provide new information about the scattering targets. However, there are currently no measurement techniques that can efficiently and quantitatively measure the OAM of free electrons, which are incoherent mixtures of energy and OAM states and therefore resistant to existing measurement techniques developed for photon OAM measurement.
Our Technology Solution: University of Oregon researchers have opened up an entirely new category of electron spectroscopy that enables the simultaneous measurement of energy spectra and OAM spectra (as a new degree of freedom) in scattered electrons. The principles of the devicse are similar to an optical log-polar transformer that can sort optical OAM modes of light. However, fundamental differences arise when applying these principles to realize a practical device. Whereas existing techniquest used to measure properties of light are implemented using shaped pieces of glass, the current devices are unique to charged particles, and have no analog in photon OAM measurement. Some devices use a spatially varying electric field around needle electrodes to measure this quantized OAM of charged particles. No equivalent technique exists for measurement of photon OAM.
Applications: The present method was developed in the context of electron microscopy and has applications in fundamental research, material characterization and eventually processing and manufacturing.