Measuring the duration of energetic electron pulses using laser fields

Dec 09, 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

Jun 04, 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

Jun 12, 2012

(Phys.org) -- 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 ...

Recommended for you

Robotics goes micro-scale

Apr 17, 2014

(Phys.org) —The development of light-driven 'micro-robots' that can autonomously investigate and manipulate the nano-scale environment in a microscope comes a step closer, thanks to new research from the ...

High power laser sources at exotic wavelengths

Apr 14, 2014

High power laser sources at exotic wavelengths may be a step closer as researchers in China report a fibre optic parametric oscillator with record breaking efficiency. The research team believe this could ...

Combs of light accelerate communication

Apr 14, 2014

Miniaturized optical frequency comb sources allow for transmission of data streams of several terabits per second over hundreds of kilometers – this has now been demonstrated by researchers of Karlsruhe ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Static
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?

More news stories

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

Scientists tether lionfish to Cayman reefs

Research done by U.S. scientists in the Cayman Islands suggests that native predators can be trained to gobble up invasive lionfish that colonize regional reefs and voraciously prey on juvenile marine creatures.

Leeches help save woman's ear after pit bull mauling

(HealthDay)—A pit bull attack in July 2013 left a 19-year-old woman with her left ear ripped from her head, leaving an open wound. After preserving the ear, the surgical team started with a reconnection ...