Zeptoseconds
By Scott Hamilton
Ahmed Zewail received the Nobel Prize in 1999 for measuring the speed at which molecules change their shapes. A result of his experiments formed a new science called femtochemistry. In femtochemistry, ultrashort flashes of laser light are used to see the formation and breakup of chemical bonds. The bonds form in the realm of femtoseconds. Up until just recently, the femtosecond was the shortest measure of time ever observed.
Earlier this month, it was published that a group of atomic physicists at Goethe University, working under the direction of Professor Reinhard Dorner, have been studying a process that is shorter than femtoseconds by magnitudes. The team successfully measured the amount of time it takes for a photon to travel across a hydrogen molecule, a distance of only 74 picometers. As it turns out, this is 247 zeptoseconds, which is the shortest timespan to be measured in history.
The group measured the phenomenon by blasting a single Hydrogen II molecule with x-rays from the most brilliant storage-ring-based x-ray radiation source, a PERTA III x-ray laser, at the Deutshes Elektronen-Synchrotron (DESY) accelerator facility in Hamburg. They set the energy level of the x-ray high enough to successfully knock both electrons out of the hydrogen molecule with a single photon. Electrons behave like particles and waves simultaneously, making it easy to detect the ejection of the electron. They were able to measure the time between the first electron being ejected and creating an electron wave and the second, 247 femtoseconds later.
You can think of the photon as acting a lot like a pebble skipping across the surface of a pond. There is a ripple created in the pond each time the pebble strikes the water. In the case of this particular experiment, the photon hit the surface twice, creating two ripples. Just like the ripples in water interfere with one another, creating a measurable interference pattern, the same thing happens with the electron waves.
The scientists used a special instrument designed to measure the ultrafast interference patterns in molecular reactions. The COLd Target Recoil Momentum Spectroscope (COLTRIMS) was used to determine the orientation of the hydrogen molecule and was able to know the exact distance between the two hydrogen atoms. Professor Dorner says, “We observed for the first time that the electron shell in a molecule does not react to light everywhere at the same time. The time delay occurs because information within the molecule only spreads at the speed of light. With this finding we have extended out COLTRIMS technology to another application.”
It always amazes me that the deeper we look into modern science, the more aspects of intricate design emerge. The fact that we are now able to detect the edges of an electron shell, but still not be able to observe individual electrons, is mind boggling to me. I am forever amazed at creation. Until next time, stay safe and learn something new.
Scott Hamilton is a Senior Expert in Emerging Technologies at ATOS and can be reached with questions and comments via email to sc************@at**.net.
