The wave nature of light in super-slow motion

July 12, 2017

Physicists at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) and Friedrich Schiller University Jena (FSU) have accomplished a quantum leap in light research. They have managed to capture the behaviour of extremely short laser pulses during focusing by means of very high spatial and temporal resolution. The results are of fundamental relevance to understanding the interactions between light and matter and will make it possible to control electron movements and chemical reactions to an extent that was previously not feasible. These insights into fundamental physics will particularly profit further research into new radiation sources and in the field of light wave electronics. The researchers recently published their findings in the leading specialist journal Nature Physics.

Ultrashort light pulses with such a wide optical spectrum range that the beams appear white are in common use nowadays. Among other things they are used to examine the retina of the eye while in physics they are employed to control processes at the atomic level and analyse them in slow motion. In almost all these applications, the white pulses need to be focused. As it is the specific form of the that determines how electrons, for example, will move within it, it is essential to know what the focused laser beam actually looks like in detail.

In order to better understand why, think of a ship in stormy seas. The helmsman not only has to know how high and how long the waves are but also has to keep an eye on incoming waves in order to know when they will hit the ship in order to find a safe path up to the crest of the wave on one side and down on the other. In the same way, it is important for researchers to know how and where the maximum of a light wave will strike electrons in an experiment or application in order to have a targeted influence on them. The changes to and propagation of light waves in an electrical field take place on a time scale of a few hundred attoseconds—in other words, within one billionth of a billionth of a second. Until recently, it was not possible to measure the exact distribution of the wave troughs and peaks at the focus of a on this time scale.

The researchers in Erlangen and Jena have now achieved this by focusing onto a nanometre-sharp metal tip, causing the tip to emit electrons. These electrons act as a kind of sensor that enables the researchers to interpret the exact form of the light wave.

Watching light travel

Almost 130 years ago, the French physicist Louis Georges Gouy (1854-1926) observed and described a phase shift that occurred during the focusing of monochromatic light when interference was introduced. This effect was named the 'Gouy phase' after its discoverer and for a long time it was assumed that the effect would be the same in the case of white laser spectra, which consist of many colours of light. The results obtained in the joint project have added to our understanding of the effect, so that even when it comes to short pulses—and to stay with the metaphor for the moment—no captain will be taken by surprise by unexpected waves in future.

Explore further: Using lasers to create ultra-short pulses

More information: Dominik Hoff et al, Tracing the phase of focused broadband laser pulses, Nature Physics (2017). DOI: 10.1038/nphys4185

Related Stories

Using lasers to create ultra-short pulses

March 15, 2017

Physicists at Friedrich-Alexander Universität Erlangen-Nürnberg (FAU) have entered new territory with regard to the pulsing of electron beams. Their method could soon be used to develop electron microscopes suitable for ...

Looking at complex light wave forms

May 31, 2017

For the first time, an international research team under the direction of Prof. Dr. Giuseppe Sansone at the Institute of Physics at the University of Freiburg has been able to completely characterize the complex evolution ...

Attosecond camera for nanostructures

May 31, 2016

Physicists based at Ludwig-Maximilians-Universitaet (LMU) in Munich and the Max Planck Institute for Quantum Optics have observed a nanoscale light-matter phenomenon which lasts for only attoseconds.

Electrons used to control ultrashort laser pulses

March 21, 2017

We may soon get better insight into the microcosm and the world of electrons. Researchers at Lund University and Louisiana State University have developed a tool that makes it possible to control extreme UV light - light ...

Recommended for you

New type of electron lens for next-generation colliders

October 18, 2017

Sending bunches of protons speeding around a circular particle collider to meet at one specific point is no easy feat. Many different collider components work keep proton beams on course—and to keep them from becoming unruly.


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.