Atomic Clock Determines Absolute Timing of Photoelectric Effect

Facebook X LinkedIn Email
VIENNA, Austria, Sept. 20, 2018 — According to scientists at the University of Vienna (TU Wien), it is now possible to measure the photoelectric effect. The TU Wien team, together with research groups from Garching, Munich, and Berlin, determined the duration of the photoelectric effect using a tungsten surface.

When light falls on certain materials, electrons are released from their surface. In attoseconds, an electron from the material will absorb a photon, “jump” into another state, and leave the surface. This phenomenon, or photoelectric effect, is so fast that until now it has mostly been regarded as instantaneous.

Determining the absolute timing of the photoelectric effect. TU Wien.
A laser pulse hits a tungsten surface on which iodine atoms have been deposited. Both the tungsten atoms and the iodine atoms lose electrons, which can then be measured. Courtesy of TU Wien.

While scientists have been able to determine the time interval between different quantum jumps and show that these different jumps take different amounts of time, until now it has only been possible to determine time differences, not the absolute duration of the process.

Using the atomic chronoscope method, which references all measured timings to the moment of light-pulse arrival, the researchers were able to determine the absolute timing of the photoelectric effect. Through experiments, computer simulations, and theoretical calculations, they discovered and defined an atomic clock that starts precisely at the beginning of the quantum jump.

To achieve an absolute, precisely calibrated reference scale, the researchers began by studying electrons removed from helium atoms by laser pulses. They used the helium atoms as a reference clock.

“The helium atom is very simple. In this case, we can accurately calculate the time evolution of the photoemission,” said professor Christoph Lemell.

In their second experiment, the researchers compared the photoemission of helium and iodine, using the comparison to calibrate an “iodine clock.” In the third and final experiment, the researchers used the iodine atoms to study the photoemission of electrons from a tungsten surface.

The researchers deposited the iodine atoms on a tungsten surface and irradiated the surface with ultrashort laser pulses. The ultrashort pulse was the starting signal for the photoelectric effect to begin. When the pulse hit the surface of the tungsten, electrons were released from their atoms and jumped to a different quantum state, a state in which they could reach the tungsten surface and leave the surface. The iodine atoms, serving as a reference clock, were used to measure the photoemission from the tungsten surface. 

“In tungsten, the duration of this process can be studied particularly well because the interface of the material can be defined very precisely there. The tungsten surface is an excellent finish line for electron-time measurement,” said professor Florian Libisch.

The team said that the duration of the photoemission process depends on the initial state of the electrons. It ranges from 100 attoseconds for electrons from the inner shells of the tungsten atoms to 45 attoseconds for conduction band electrons, which on average pass the finish line faster.

The researchers’ goals extend beyond purely measuring the duration of a quantum effect. The photoelectric effect plays an important role in many fields, for example in solar cells or in the conversion of data from a fiber optic cable into electrical signals.

"It is an exciting field of research that provides remarkable new insights — for example into surface physics, and into electron transport processes inside materials,” said professor Joachim Burgdörfer. “It gives us the opportunity to study important physical processes with an accuracy that would have been inconceivable a few years ago.”

The measurements were carried out at the Max Planck Institute for Quantum Optics. Scientists from the TU Wien were responsible for the theoretical work and computer simulations.

The research was published in Nature (doi:10.1038/s41586-018-0503-6).

Published: September 2018
The term quantum refers to the fundamental unit or discrete amount of a physical quantity involved in interactions at the atomic and subatomic scales. It originates from quantum theory, a branch of physics that emerged in the early 20th century to explain phenomena observed on very small scales, where classical physics fails to provide accurate explanations. In the context of quantum theory, several key concepts are associated with the term quantum: Quantum mechanics: This is the branch of...
Metrology is the science and practice of measurement. It encompasses the theoretical and practical aspects of measurement, including the development of measurement standards, techniques, and instruments, as well as the application of measurement principles in various fields. The primary objectives of metrology are to ensure accuracy, reliability, and consistency in measurements and to establish traceability to recognized standards. Metrology plays a crucial role in science, industry,...
atomic clock
An atomic clock is a highly precise timekeeping device that uses the vibrations or oscillations of atoms as a reference for measuring time. The most common type of atomic clock uses the vibrations of atoms, typically cesium or rubidium atoms, to define the length of a second. The principle behind atomic clocks is based on the fundamental properties of atoms, which oscillate at extremely stable and predictable frequencies. The primary concept employed in atomic clocks is the phenomenon of...
photoelectric effect
The emission of an electron from a surface that occurs when a photon impinges upon the surface and is absorbed. This effect is the means by which photons may be detected.
TU WienUniversity of ViennaResearch & TechnologyeducationEuropequantummetrologyOpticsTest & Measurementpulsed lasersoptical metrologyattosecondatomic clockphotoelectric effectspectroscopyquantum jumpMaterialsphotoemissionEuro News

We use cookies to improve user experience and analyze our website traffic as stated in our Privacy Policy. By using this website, you agree to the use of cookies unless you have disabled them.