Thursday, December 16, 2010

Blog on OAM and optical tweezers

Blog on OAM and optical tweezers

Thursday, September 16, 2010

Production and application of electron vortex beams

Production and application of electron vortex beams

J. Verbeeck1, H. Tian1 & P. Schattschneider2

Electron Microscopy for Materials Science (EMAT), University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
Institute for Solid State Physics and University Service Centre for Electron Microscopy, Vienna University of Technology, A-1040 Vienna, Austria
Correspondence to: J. Verbeeck1 Email:

Top of pageAbstract
Vortex beams (also known as beams with a phase singularity) consist of spiralling wavefronts that give rise to angular momentum around the propagation direction. Vortex photon beams are widely used in applications such as optical tweezers to manipulate micrometre-sized particles and in micro-motors to provide angular momentum1, 2, improving channel capacity in optical3 and radio-wave4 information transfer, astrophysics5 and so on6. Very recently, an experimental realization of vortex beams formed of electrons was demonstrated7. Here we describe the creation of vortex electron beams, making use of a versatile holographic reconstruction technique in a transmission electron microscope. This technique is a reproducible method of creating vortex electron beams in a conventional electron microscope. We demonstrate how they may be used in electron energy-loss spectroscopy to detect the magnetic state of materials and describe their properties. Our results show that electron vortex beams hold promise for new applications, in particular for analysing and manipulating nanomaterials, and can be easily produced.

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Quantum tornado in the electron beam

Quantum tornado in the electron beam

(Nanowerk News) Manipulating materials with rotating quantum particles: a team from the University of Antwerp and TU Vienna (Professor Peter Schattschneider, Institute of Solid State Physics) has succeeded in producing what are known as vortex beams: rotating electron beams, which make it possible to investigate the magnetic properties of materials. In the future, it may even be possible to manipulate the tiniest components in a targeted manner and set them in rotation. The physicists report on this breakthrough in electron physics and its application in the current edition of Nature ("Production and application of electron vortex beams").
Rotating current: the quantum tornado
Electron beams have been used to analyse materials for some time now – for example in electron microscopes. For the most part, the beams' rotation does not affect this analysis. In classical physics, an electron current in a vacuum does not have any orbital angular momentum. In quantum mechanics, however, the electrons must be envisaged as a wavelike current – which can rotate as a whole about its propagation direction, similar to the air flow in a tornado.

A flat wave (left) meets the specially shaped grid screen, which converts the electron beam into right-rotating and left-rotating vortex beams (top and bottom), and a middle beam that does not rotate. Similar to in a tornado, the rotation of the electron current is low internally

Vortex light beams have been used in optics for some time (for example, as optical tweezers for manipulating small particles). Vortex beams made from electrons also offer many new possibilities for managing nanoparticles or measuring angular momentum-related parameters. However, there were previously no really efficient methods of producing them. "When I was working on an idea of how these beams could be technically produced, it emerged that colleagues from Antwerp had had the same idea", explains Prof Schattschneider. "We therefore decided to pursue the project together: Antwerp had progressed further with the production and Vienna came up with a suggestion for the first application."

The trick with the screen

The production of vortex electron beams was made possible with the help of a grid-like screen cut from platinum foil. When it passes through the platinum screen, the electron beam is diffracted in a similar way to light beams when they pass through a fine grid. The shape of this screen, which measures only a few millionths of a metre, was specifically calculated so that a flat incident electron wave is converted into vortex beams. Right-rotating and left-rotating vortex beams are thus formed behind the grid and in the middle there is a conventional electron beam that does not rotate.

If the electrons are used to irradiate a material which for its part also influences the angular momentum of the electrons, and if the electrons are subsequently directed through the made-to-measure platinum screen, then, after this, either the right-rotating or the left-rotating vortex beam will be more intense. "This enables us to investigate processes affected by angular momentum in nanomaterials much more precisely than was previously possible", explains Prof Schattschneider.
Better than science fiction
The physicist, who also occasionally writes science fiction, does not find it hard to imagine more exotic applications for the vortex beams: "These electron beams could be used in a targeted way to set tiny wheels in motion on a microscopic motor. Also, the magnetic field of the rotating electrons could be used in the tiniest length scales", Schattschneider speculates. Even applications in data transfer (quantum cryptography) and quantum computers are feasible.
Source: Vienna University of Technology

Monday, August 2, 2010

Orbital angular momentum in radio: Measurement methods

Orbital angular momentum in radio: Measurement methods
Mohammadi, Siavoush M.; Daldorff, Lars K. S.; Forozesh, Kamyar; Thidé, Bo; Bergman, Jan E. S.; Isham, Brett; Karlsson, Roger; Carozzi, T. D.
AA(Department of Electrical and Computer Engineering, Interamerican University of Puerto Rico, Bayamón, Puerto Rico); AB(Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden); AC(Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden); AD(Swedish Institute of Space Physics, Uppsala, Sweden); AE(Swedish Institute of Space Physics, Uppsala, Sweden); AF(Department of Electrical and Computer Engineering, Interamerican University of Puerto Rico, Bayamón, Puerto Rico); AG(Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden); AH(Department of Physics and Astronomy, University of Glasgow, Glasgow, UK)
Radio Science, Volume 45, Issue 4, CiteID RS4007 (RaSc. Homepage)
Publication Date:
AGU Keywords:
Radio Science: Radio wave propagation, Radio Science: Instruments and techniques (1241), Radio Science: Radio astronomy
Abstract Copyright:
(c) 2010: American Geophysical Union
Bibliographic Code:

Wednesday, July 28, 2010

Orbital Angular Momentum – Bo Thide and Jan Bergman (SETI Talks)

Link to SETI Archive: On the extraction of all information embedded in radio siganls: Implications for SETI: A new idea for utilizing all of the information in photons for communication involves a little-know electromagnetic property: the photon’s orbital angular momentum (POAM). The communication and computer industries are actively looking at the possibilities. We will discuss current research and the implications for SETI.

Thursday, April 1, 2010

Generation of electron beams carrying orbital angular momentum

Generation of electron beams carrying orbital angular momentum

Nature 464, 737 (2010). doi:10.1038/nature08904

Authors: Masaya Uchida & Akira Tonomura
All forms of waves can contain phase singularities. In the case of optical waves, a light beam with a phase singularity carries orbital angular momentum, and such beams have found a range of applications in optical manipulation, quantum information and astronomy. Here we report the generation of an electron beam with a phase singularity propagating in free space, which we achieve by passing a plane electron wave through a spiral phase plate constructed naturally from a stack of graphite thin films. The interference pattern between the final beam and a plane electron wave in a transmission electron microscope shows the ‘Y’-like defect pattern characteristic of a beam carrying a phase singularity with a topological charge equal to one. This fundamentally new electron degree of freedom could find application in a number of research areas, as is the case for polarized electron beams.

Author: Masaya Uchida