e., the Fraunhofer plane), as shown in Fig. In order to stop one of the two beams passing to the left and right of the biprism, it was necessary to use an aperture A, which was inserted in a region where they were widely separated, corresponding approximately to the back focal plane of the imaging lens ( i. Two beam interference fringes could be observed in the observation plane OP, which was situated in the Fresnel region with respect to the biprism, as the standard gaussian image only showed its bare dark shadow. In the first experiment in which an electron biprism was used as an interferometry device 17, a biprism was inserted in the normal specimen plane, where it could be biased in a specimen holder with contacts connected to an external voltage source. The possibility of continuously varying the excitations of the electron lenses also allows planes in the Fresnel region between these two primary planes to be imaged. This plane can be optically conjugate to the observation plane OP, which can be the specimen plane if a gaussian image is desired, or the Fraunhofer diffraction plane (coincident with the back focal plane of the imaging lens for plane wave illumination) if a diffraction image is desired. As a result of the small de Broglie wavelength of high energy electrons, a further system of magnifying lenses is necessary so that interference fringe details can be resolved by an electron detector in the final recording plane. In general, the illumination system comprises an electron source followed by a system of condenser lenses, which demagnify the source, so that partial coherence does not blur the desired interference phenomena. We first recall a few basic concepts in electron optics and microscopy. After describing the drawbacks of former setups, we show how they can now be overcome by using a modern electron holography microscope that is equipped with two electron biprisms and a high brightness gun and how a new version of the experiment, in which the fringes are observed in the image instead of the Fraunhofer plane, can be realized. Although conceptually and mathematically simple, at least from the point of view of wave optical analysis 22, 23, its experimental realization is a very challenging task that requires advanced technology and instrumentation, as demonstrated by the partial success of former attempts 8, 17. It is then possible to observe the transition of the diffraction pattern from the two- to the one-slit configuration, highlighting the wave-particle duality of the electrons. Here, we focus on the second part of the Young-Feynman experiment, which refers to the change in the interference pattern when one of the two slits is partially or totally obstructed in a controllable way. Inelastic scattering in the material can be regarded as a dissipative process during the interaction, which is responsible for the localization mechanism 20, 21. First experiments in this direction have been carried out by preparing nano-slits and depositing a layer of amorphous material using modern nanotechnology tools on one 18 or both 19 of them. The third part of the Young-Feynman experiment, which has subsequently been renamed the which-way (or which-path) experiment, aims at demonstrating that interference phenomena disappear when the setup is modified to obtain information about which slit the electron passes through. It has been performed in a controlled manner by stopping one of the two beams in the Fraunhofer image of an electron biprism 17 or in the Fresnel image of two slits 8. Its analysis leads to the idea of the probability amplitude. The second part of the Young-Feynman experiment involves a comparison of electron distributions recorded before and after one of the slits is closed 16. The build-up of two beam Fresnel interference fringes using single electrons was first demonstrated using an electron biprism as a wavefront beam splitter 14, 15. Two beam interference patterns can be observed using a Möllenstedt-Düker electron biprism 9, 10, which has proved to be the most versatile method for carrying out interferometry and holography experiments (see, e. The first part involves the observation of interference fringes in a double slit setup 3, 4, 5, 6 and their build-up using single electrons 7, 8. The Young-Feynman experiment consists of three parts. Recent advances in electron optics, nanotechnology and specimen preparation have resulted in many studies on the experimental realization of the double-slit thought or gedanken experiment, which was described by Feynman as containing all of the mysteries of quantum mechanics 1, 2, using single free electrons.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |