Measuring the duration of energetic electron pulses using laser fields

December 9, 2013 by Thorsten Naeser
Measuring the duration of energetic electron pulses using laser fields
A view of the electron diffraction laboratory. Here, the microcosmos is being explored with ultrashort bursts of electrons. A new stopwatch made of light makes it possible to measure the pulses exactly, and is potentially capable of attaining attosecond precision. Credit: Thorsten Naeser

A stopwatch made of light can determine the duration of extremely brief electron flashes. Teams based in the Laboratory for Attosecond Physics (LAP) at LMU and at the Max Planck Institute of Quantum Optics have, for the first time, succeeded in measuring the lengths of ultrashort bursts of highly energetic electrons using the electric fields of laser light. Such electron pulses, which behave like ultrashort matter waves, provide time-resolved recordings of processes taking place in molecules and atoms, enabling elementary particles to be "filmed" in four dimensions. The new stopwatch for electrons now permits even more precise investigations of the motions of electrons and atoms on nature's smallest scales.

A temporal resolution of 24 frames per second is sufficient for a succession of still images to be perceived as smooth motion by the human eye. Recording the motions of and charges within matter, which occur on attosecond scales, requires the acquisition of images at a trillion times that rate.  The use of electron pulses offers a way to capture such ultrafast processes. Bunches of electrons can be kicked out of a metal surface using laser light. Each electron pulse lasts for a few femtoseconds (a femtosecond is 1000 attoseconds; an attosecond is a billionth of a billionth of a second) and can deliver an almost instantaneous shot of processes within atoms.

However, exactly how long such pulses last has been difficult to determine. Now the LAP team has developed a system for the precise measurement of the duration of energetic (25 keV) electron pulses. The researchers direct the electron pulses at a thin foil of aluminum. There, they interact with a laser pulse which impinges on the foil perpendicularly to the electrons. Under the influence of the laser's electric field, the electrons either gain or lose some energy before passing straight through the foil to a detector. Whether electrons pick up or lose energy during the encounter depends on the precise timepoint at which they interact with the rapidly oscillating electromagnetic laser field. From the energy spectrum at the , the scientists can deduce the duration of the original electron pulse prior to its interaction with the laser field.

In contrast to the photons that make up , can penetrate deep into the inner constituents of matter. Hence, they not only measure the chronological sequence of events, but also probe the spatial dispositions of the atoms during a reaction. The investigation of matter with extremely brief electron pulses is called "ultrafast electron diffraction". With this technique, one can determine the positions and movements of atoms and charges in both space and time ‒ i.e. in four dimensions. It is now possible to produce electron pulses that last for several hundreds of femtoseconds but, in principle, even attosecond electron flashes can be generated for . And when they eventually become available, these still shorter electron bunches can also be measured with the new technique. With the new stopwatch made of light, that novel regime no longer seems so far away.

Explore further: Electron spectroscopy: Not just snapshots, real movies

More information: F. O. Kirchner, A. Gliserin, F. Krausz  und P. Baum. "Laser streaking of free electrons at 25 keV."
Nature Photonics, DOI: 10.1038/nphoton.2013.315, 8 December 2013

Related Stories

Cool electron acceleration

June 4, 2013

Physicists from the Max-Planck-Institute of Quantum Optics produced electron pulses from a laser accelerator whose individual particles all have nearly the same, tuneable energy.

Flashes of light out of the mirror

June 12, 2012

( -- A team of the Laboratory of Attosecond physics at the Max Planck Institute of Quantum Optics developed an alternative way of generating attosecond flashes of light. 

X-rays in the fast lane

May 10, 2013

X-ray free-electron lasers (XFELs) produce higher-power laser pulses over a broader range of energies compared with most other x-ray sources. Although the pulse durations currently available are enormously useful for the ...

Recommended for you

Making silicon-germanium core fibers a reality

October 25, 2016

Glass fibres do everything from connecting us to the internet to enabling keyhole surgery by delivering light through medical devices such as endoscopes. But as versatile as today's fiber optics are, scientists around the ...

Controlling ultrasound with 3-D printed devices

October 25, 2016

Ultrasound is more than sound. Obstetricians use it to peer inside a woman's uterus and observe a growing baby. Surgeons use powerful beams of ultrasound to destroy cancer cells. Researchers fire ultrasound into materials ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Dec 09, 2013
This = awesome. Anyone else waiting until we have engineers designing chemical reactions that play out to look like movies?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.