Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

K-State's fast laser research and theory building on Einsten's work by timing electrons emissions

26.05.2009
Ultrafast laser research at Kansas State University has allowed physicists to build on Nobel Prize-winning work in photo-electronics by none other than Albert Einstein.

Einstein received the Nobel Prize in 1921 for his theoretical explanation in 1905 of the so-called photo-effect -- that is, the emission of electrons from a metal surface by incident light.

In Einstein's time, laboratory light sources provided light of very low intensity in comparison with modern lasers like those at K-State. Back then, experiments could measure the energy -- or speed -- of light-emitted electrons but could not resolve their motion in time. In modern laboratories, lasers are used as light sources that provide very short and intensive flashes of light.

Uwe Thumm, K-State professor of physics, and Chang-hua Zhang, a postdoctoral research associate in physics, are theorists who have developed a model that allows them to compute not just the energy of photo-emitted electrons, but also the times after their release at which they can be detected. Within their quantum mechanical model, Thumm and Zhang found that electrons that are emitted by ultra-short laser pulses from different parts of a metal surface will arrive at an electron detector at slightly different times.

"It's a feat that would be impossible without high-intensity lasers like those at K-State's J. R. Macdonald Laboratory," Thumm said. "With the help of ultrashort laser pulses, the motion of electrons can now be followed in time. This has started an entire new area of research, called attosecond physics."

An attosecond is a billionth of a billionth of a second. It's an incredibly short time to humans -- but not to electrons, Thumm said.

"Fifty attoseconds is about the time resolution needed to resolve the motion of electrons in matter," he said.

In agreement with a recent experiment, their calculation shows that electrons of a metal surface that are near atomic nuclei are photo-emitted with a delay of about 110 attoseconds relative to another type of electron. These conduction electrons are not attached to individual atoms and enable metals to conduct electricity.

Thumm and Zhang published their work in Physical Review Letters in March. Their research was supported by the National Science Foundation and the U.S. Department of Energy.

Thumm said that Einstein's research, which laid the groundwork for their own research, is often understood as a proof for light behaving as a particle called a photon rather than as a wave. Einstein showed that only light above a certain minimal frequency -- in the blue end of the visible spectrum -- could make metals emit electrons.

"It was a celebrated model, and it's still in textbooks as an explanation that light is made up of photons," Thumm said. "You can talk to a lot of physics students who get it wrong."

While Einstein's model is not wrong, it is not a proof for the particle-character of light, Thumm said. Einstein published his model about two decades before modern quantum theory was developed. Modern quantum theory of matter predicts the emission of an electron even when light is regarded as a classical electro-magnetic wave.

Today, physicists have lasers that provide light at such high intensities that electrons can be emitted at lower frequencies, toward the red end of the visible spectrum. And today, scientists look at light as behaving both like a particle and a wave.

"There is a bit of a philosophical debate," Thumm said.

Thumm said that the new and exciting part of this research is that short pulses from ultrafast lasers like the Kansas Light Source at K-State's J.R. Macdonald Lab allow physicists to measure the timing of electrons emitting from metals, thus building on models like the one he and Zhang developed.

Researchers can use short, intense pulses of extreme ultraviolet light to get a tungsten surface to emit electrons. They can synchronize these extreme ultraviolet pulses with a delayed infrared pulse, into which the electron is emitted. Thumm said that this infrared pulse changes the energy of the emitted electrons over time and serves as a measuring stick to judge the timing of the electron emissions.

He said that it is a bit like how high-speed photography in the 19th century proved that all four of a horse's hooves leave the ground while running.

"In this case it's not the horse's hooves but the electrons that we're seeing," Thumm said. "The bigger picture is that if we resolve in time how electrons move, we can understand the timing of chemical reactions taking place. We can understand the basics of chemistry, biology and life."

While Thumm and other K-State physicists continue to delve further into attosecond research, the university will be host to the Second International Conference on Attosecond Physics from July 28 to Aug. 1, bringing physicists from around the world to the K-State campus in Manhattan.

Uwe Thumm | EurekAlert!
Further information:
http://www.ksu.edu
http://jrm.phys.ksu.edu

More articles from Physics and Astronomy:

nachricht Pulses of electrons manipulate nanomagnets and store information
21.07.2017 | American Institute of Physics

nachricht Vortex photons from electrons in circular motion
21.07.2017 | National Institutes of Natural Sciences

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

NASA looks to solar eclipse to help understand Earth's energy system

21.07.2017 | Earth Sciences

Stanford researchers develop a new type of soft, growing robot

21.07.2017 | Power and Electrical Engineering

Vortex photons from electrons in circular motion

21.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>