Realization of a tilted reference wave for electron holography by means of a condenser biprism

As proposed recently, a tilted reference wave in off-axis electron holography is expected to be useful for aberration measurement and correction. Furthermore, in dark-field electron holography, it is considered to replace the reference wave, which is conventionally diffracted in an unstrained object...

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Bibliographic Details
Published in:Ultramicroscopy 2016-02, Vol.161, p.23-40
Main Authors: Röder, Falk, Houdellier, Florent, Denneulin, Thibaud, Snoeck, Etienne, Hÿtch, Martin
Format: Article
Language:English
Subjects:
Aberration
Beams (radiation)
Camber
Chemical Sciences
Coherence
Condensed Matter
Condenser biprism
Cristallography
Dark-field electron holography
Diffraction
Holography
Illumination
Instrumentation and Detectors
Materials Science
Off-axis electron holography
Other
Physics
Planes
Tilt
Tilted reference wave
Transmission cross-coefficient
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Summary:As proposed recently, a tilted reference wave in off-axis electron holography is expected to be useful for aberration measurement and correction. Furthermore, in dark-field electron holography, it is considered to replace the reference wave, which is conventionally diffracted in an unstrained object area, by a well-defined object-independent reference wave. Here, we first realize a tilted reference wave by employing a biprism placed in the condenser system above three condenser lenses producing a relative tilt magnitude up to 20/nm at the object plane (300kV). Paraxial ray-tracing predicts condenser settings for a parallel illumination at the object plane, where only one half of the round illumination disc is tilted relative to the optical axis without displacement. Holographic measurements verify the kink-like phase modulation of the incident beam and return the interference fringe contrast as a function of the relative tilt between both parts of the illumination. Contrast transfer theory including condenser aberrations and biprism instabilities was applied to explain the fringe contrast measurement. A first dark-field hologram with a tilted – object-free – reference wave was acquired and reconstructed. A new application for bright/dark-field imaging is presented.
ISSN:0304-3991
1879-2723
DOI:10.1016/j.ultramic.2015.11.004