Synopsis: A Crystalline Undulator

The periodically varying electromagnetic field inside a crystal can be exploited to build an undulator that emits gamma rays.
Synopsis figure
Tobias N. Wistisen/Aarhus University

Undulators are periodic arrangements of magnets that are used as insertion devices at synchrotron light sources. Through their alternating magnetic field, they cause the relativistic electron beam in the synchrotron ring to wiggle and thereby emit a beam of coherent radiation. Existing undulators can produce light with wavelengths as short as a tenth of an angstrom (the “hard” x-ray regime). But reaching even shorter wavelengths, which could penetrate deeper into materials and probe their structure with greater resolution, is problematic: emission wavelengths are proportional to the period of the undulator magnets, and scaling it down poses a technological challenge. Now, as reported in Physical Review Letters, researchers have realized a “crystalline undulator,” in which the field periodicity is not provided by magnets but by the extremely strong internal electromagnetic field from the atoms of the crystal.

The team, led by Ulrik Uggerhøj at Aarhus University in Denmark realized a scheme theorized by Andriy Kostyuk in 2013. The authors directed a beam of relativistic electrons onto a silicon-germanium crystal with periodically bent crystallographic planes. Inside the crystal, the electrons followed a sinusoidal path determined by the shape of the bent planes, thereby emitting radiation. As in an undulator, the emitted radiation was enhanced at specific resonant wavelengths determined by the crystalline periodicity. The largest enhancement was observed at a few megaelectronvolts—a gamma-ray wavelength inaccessible by current undulator technologies. So far, the device’s emission is broad, lacking the coherence of conventional undulators, but the design of optimized crystals could lead to more sharply defined frequencies. Crystal undulators could serve as compact light sources operating in previously inaccessible hard x-ray and gamma-ray regimes. – Matteo Rini


More Features »


More Announcements »

Subject Areas

OpticsMaterials Science

Previous Synopsis

Next Synopsis

Related Articles

Focus: 3D Images 10 Times Faster
Interdisciplinary Physics

Focus: 3D Images 10 Times Faster

3D x-ray phase-contrast images take as little as one-tenth the usual time to acquire using a technique that halves the number of required “photos.” Read More »

Synopsis: A Crystal Ball for 2D Materials
Materials Science

Synopsis: A Crystal Ball for 2D Materials

Researchers predict new two-dimensional materials whose structures differ from their three-dimensional counterparts. Read More »

Viewpoint: Electron Pulses Made Faster Than Atomic Motions
Atomic and Molecular Physics

Viewpoint: Electron Pulses Made Faster Than Atomic Motions

Electron pulses have shattered the 10-femtosecond barrier at which essentially all atomic motion is frozen in materials. Read More »

More Articles