The development of the first laser in 1960 marked the beginning of commercial applications for light that are now ingrained in our day-to-day lives. Simultaneously, this improvement opened up the logical field of laser spectroscopyica procedure that is key to the investigation of materials and the investigation of principal physical peculiarities.
However, despite all of the successes, researchers have struggled since the 1970s with the issue of a sample being excited multiple times during an experiment by a laser beam. It is difficult to comprehend the material in this instance because the measurement results for the single and multiple excitations overlap and typically cannot be separated.
To address this issue, laser power is typically reduced to the point where multiple excitations are less likely than one excitation.Nonetheless, they can’t be totally avoided and can subsequently prompt wrong understandings of the information. It is still challenging to distinguish between two, three, four, or even more excitations, even when multiple excitations themselves are the focus of the investigation.
“Separation of signals from single and multiple excitations is especially beneficial for large systems with densely packed light absorbers, such as natural photosynthetic complexes or organic materials.”
First author Pavel Malý, is now a researcher at Charles University in Prague,
This decades-old issue has now been resolved by a team of physicists and physical chemists from the University of Ottawa in Canada and the Julius-Maximilians-Universität Würzburg (JMU). In the most recent issue of Nature, they describe their method. The common technique of “transient absorption” was utilized by the researchers in the experiment carried out by Professor Tobias Brixner’s group at Würzburg to track extremely rapid changes in a variety of materials that take place in a millionth of a millionth of a second.
The researchers combined the data using a newly derived formula, whereas the conventional approach employs a single laser. They were able to systematically differentiate the effects from a single to a six-fold excitation in this manner.
According to Brixner, “especially with such a simple procedure that any spectroscopic research group can implement and use without much additional effort,” “Not so long ago, I wouldn’t have thought that such a distinction was even possible.”
However, obtaining the “recipe” was anything but straightforward and necessitated an in-depth investigation. “The interaction of light and matter is so rich, and we’ve demonstrated a beautiful structure hiding inside it,” says collaborator and theorist Professor Jacob Krich of the University of Ottawa. We were all really taken aback by how well this method worked for any sample you wanted to study.
Applications from photosynthesis to materials science
The new strategy has many likely applications. “Separation of signals from single and multiple excitations is particularly useful for large systems with densely packed light absorbers, such as natural photosynthetic complexes or organic materials,” states first author Pavel Mal, who was a postdoctoral fellow with Brixner at the time of the study.
The authors intend to improve the method in the future to better understand, for instance, energy transport in novel photovoltaic materials.
More information: Pavel Malý et al, Separating single- from multi-particle dynamics in nonlinear spectroscopy, Nature (2023). DOI: 10.1038/s41586-023-05846-7
