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A generalized procedure for the in situ application of magnetic fields by means of the excitation of the objective lens for magnetic imaging experiments in Lorentz microscopy and electron holography is quantitatively described. A protocol for applying magnetic fields with arbitrary in-plane magnitude and orientation is presented, and a freeware script for Digital Micrograph(™) is provided to assist the operation of the microscope. Moreover, a method to accurately reconstruct hysteresis loops is detailed. We show that the out-of-plane component of the magnetic field cannot be always neglected when performing quantitative measurements of the local magnetization. Several examples are shown to demonstrate the accuracy and functionality of the methods., (© 2013 Elsevier B.V. All rights reserved.)

The signal-to-noise ratio of measurements by electron holography could be considerably improved if longer exposure times were possible: increasing the number of electrons contributing to the hologram improves the counting statistics. However, instrumental instabilities causing drift in the hologram fringes and specimen position make acquisition times of above a few seconds counterproductive. The current approach is to acquire image stacks of holograms, with short exposure times, followed by numerical realignment through sophisticated post-processing. The associated data storage and manipulation make in-situ and tomography experiments extremely cumbersome. Here, we implement dynamic automation of electron holography experiments to overcome these problems. The real-time drift measurement and feedback control of the instrument allow single holograms to be acquired with exposure times of 30 min or more. Indeed, there are no longer any limitations from instrumental instabilities and only those imposed by the specimen itself. Furthermore, automation allows the implementation of sophisticated phase reconstruction techniques based on precise control of the experimental conditions. Smart acquisition of electron holograms preludes future computer-controlled electron microscopy capabilities. [ABSTRACT FROM AUTHOR]

• We report electron holography experiments performed with femtosecond electron pulses, using a coherent UTEM based on a laser triggered cold field emission source. • We have determined the optimum experimental conditions related to the long acquisition times imposed by the low emission/probe current available. • Holograms are acquired in vacuum and on a nano-object showing that useful physical properties can nevertheless be extracted from the hologram phase in pulsed condition. • We have implemented acquisition of short exposure time holograms assembled in a stack, combined with a computer-assisted fringes shift compensation which paves the way to ultrafast time-resolved electron holography using pump-probe setup. We report on electron holography experiments performed with femtosecond electron pulses in an ultrafast coherent Transmission Electron Microscope based on a laser-driven cold field emission gun. We first discuss the experimental requirements related to the long acquisition times imposed by the low emission/probe current available in these instruments. The experimental parameters are first optimized and electron holograms are then acquired in vacuum and on a nano-object showing that useful physical properties can nevertheless be extracted from the hologram phase in pulsed condition. Finally, we show that the acquisition of short exposure time holograms assembled in a stack, combined with a computer-assisted shift compensation of usual instabilities encountered in holography, such as beam and biprism wire instabilities, can yield electron holograms acquired with a much better contrast paving the way to ultrafast time-resolved electron holography. [ABSTRACT FROM AUTHOR]