Description:
University of Oregon Researchers: Benjamin McMorran
Patent: 9,240,255 issued 1/19/2016 (UO-13-07)
Device and Method for Creating Gaussian Electron Beams.
Technology Background/Definition of Problem: Electron beams used in instrumentation such as scanning electron microscopes, transmission electron microscopes, microprobes, etc. exhibit numerous deficiencies that limit the performance of these instruments. For example, electron beams are generally defined by apertures with hard edges, usually circular. Diffraction from these hard-edge apertures results in a beam profile known as an Airy disc, which can result in an undesirable point spread function (PSF) for the instrument. For applications where a tightly focused electron beam is used to form an image, it may be desirable to use a probe beam that has a different intensity profile, such as that described by a Gaussian distribution. In optical devices this is usually achieved using a Gaussian aperture. Such an aperture will not work for electron optical systems, however, due to incoherent scattering within the aperture material. In addition, electron beam optical systems typically exhibit aberrations that limit electron beam focusing and imaging.
Our Technology Solution: University of Oregon researchers have created a design for shaping electron beams using phase gratings, yielding precise control over beam shapes including Gaussian distributions. Grating diffraction efficiency can be spatially varied, such that a beam is diffracted most efficiently at the center of the grating, less efficiently near the edges, and not at all far away from the center of the grating. In some cases, phase gratings can be formed by periodically varying the thickness of a transparent material. By periodically patterning a transparent substrate, a periodic phase can be imprinted onto a transmitted beam. The beam then diffracts into multiple beams at discrete angles (diffraction orders). A diffraction efficiency, defined as a ratio between the intensity in a first diffraction order to that of the incident beam, is a function of the modulated optical path length (OPL) difference. In other examples, grating pitch (grating phase) is varied instead.
Applications: The present method was developed in the context of electron microscopy but has applications where other electron beams are used, including manufacturing/material processing, imaging, and medical therapy.