title: Prospects for quantitative and time-resolved double and continuous exposure off-axis electron holography.
abstract: The technique of double exposure electron holography, which is based on the superposition of two off-axis electron holograms, was originally introduced before the availability of digital image processing to allow differences between electron-optical phases encoded in two electron holograms to be visualised directly without the need for holographic reconstruction. Here, we review the original method and show how it can now be extended to permit quantitative studies of phase shifts that oscillate in time. We begin with a description of the theory of off-axis electron hologram formation for a time-dependent electron wave that results from the excitation of a specimen using an external stimulus with a square, sinusoidal, triangular or other temporal dependence. We refer to the more general method as continuous exposure electron holography, present preliminary experimental measurements and discuss how the technique can be used to image electrostatic potentials and magnetic fields during high frequency switching experiments.
authors.affiliation: Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Grünberg Institute, Forschungszentrum Jülich, D-52425 Jülich, Germany. Electronic address: v.migunov@fz-juelich.de.
authors.forename: Vadim
authors.initials: V
authors.lastname: Migunov
authors.affiliation: Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Grünberg Institute, Forschungszentrum Jülich, D-52425 Jülich, Germany; Department of Physics, Arizona State University, Tempe, AZ 85287, USA.
authors.forename: Christian
authors.initials: C
authors.lastname: Dwyer
authors.affiliation: Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Grünberg Institute, Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: Chris B
authors.initials: CB
authors.lastname: Boothroyd
authors.affiliation: Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Grünberg Institute, Forschungszentrum Jülich, D-52425 Jülich, Germany; Department of Physics and Astronomy, University of Bologna, viale B. Pichat 6/2, Bologna 40127, Italy.
authors.forename: Giulio
authors.initials: G
authors.lastname: Pozzi
authors.affiliation: Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Grünberg Institute, Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: Rafal E
authors.initials: RE
authors.lastname: Dunin-Borkowski
keywords: Continuous exposure electron holography; Double exposure electron holography; Off-axis electron holography; Transmission electron microscopy