A team of physicists at ETH Zürich in Switzerland has produced the shortest-ever laser pulses: just 43 attoseconds (an attosecond is an incomprehensible quintillionith of a second). The feat surpasses the prior record of 53 attoseconds, set earlier this year.
These 43-attosecond pulses will allow physicists to observe in high detail how electrons move within a molecule or how chemical bonds are formed.
“Molecules rotate in the range of picoseconds (10-12 s), their atoms vibrate in the range of femtoseconds (10-15 s), and the electrons move in the range of attoseconds (10-18 s),” the researchers explained.
“Starting from an infrared laser, we generate a soft X-ray laser pulse with a very large spectral bandwidth.”
“As a result, various elements including phosphorus and sulfur can be directly observed by exciting their inner-shell electrons. Both elements are present in biomolecules, and it is now possible to observe them with unprecedented time resolution.”
But what is the advantage of being able to observe the reaction steps now with even higher resolution?
“The faster a charge transfer can take place, the more efficiently a reaction can proceed,” said ETH Professor Hans Jakob Wörner.
“The human eye for example is very efficient when it comes to converting photons into nerve signals.”
“In rhodopsin, a visual pigment in the retina, the photosensitive molecule retinal is prearranged in such a way that its structure can change extremely fast through the absorption of only a single photon. This enables the visual process even in twilight.”
“A much slower reaction would render vision impossible, because the energy of the photon would be converted to heat in only a few picoseconds.”
Attosecond spectroscopy could contribute to the development of more efficient solar cells since it is now for the first time possible to follow the process of excitation through sunlight up to the generation of electricity step by step.
A detailed understanding of the charge transfer pathway could help optimizing the efficiency of the next generation of photosensitive elements.
“Attosecond laser spectroscopy is not only suitable for mere observation,” Professor Wörner said.
According to the team, chemical reactions can also be directly manipulated.
“Using a laser pulse can alter the course of a reaction — even chemical bonds can be broken by stopping the charge shift at a certain location in the molecule. Such targeted interventions in chemical reactions have not been possible until now, since the time scale of electron movement in molecules was previously unreached,” the scientists said.
“We’re already working on the next generation of even shorter laser pulses.”
“These will make it possible to record even more detailed images, and thanks to a wider X-ray spectrum even more elements can be probed than before.”
“Soon it will be possible to follow the migration of electrons in more complex molecules with an even higher time resolution.”
The results of this research are published online in the journal Optics Express.
Thomas Gaumnitz et al. 2017. Streaking of 43-attosecond soft-X-ray pulses generated by a passively CEP-stable mid-infrared driver. Optics Express 25 (22): 27506-27518; doi: 10.1364/OE.25.027506