uOttawa, University of Würzburg scientists make breakthrough in study of light

Physicists and physical chemists from the University of Würzburg and the University of Ottawa have solved a decades-old problem of distinguishing single and multiple light excitations.

“Laser light is widely used to learn about many kinds of materials using a broad set of techniques called spectroscopy,” says uOttawa physics and SUNLAB professor, and study co-author Jacob Krich. “We have developed a new spectroscopic method that is easy to apply and gives access to information about what happens when materials absorb more than one photon.”

The interaction of laser light with all kinds of materials is used to learn about biological, chemical and solid-state systems. Frequently, researchers are interested in the behaviour of materials after they’ve been “excited” just once — that is, after they absorb a single photon. To reach this limit, scientists turn down the power in the laser, which makes signals harder to measure and noisier.

The method developed by the team of physicists and physical chemists has a broad range of applications. It would be particularly useful in studying systems with closely-packed light absorbers, such as those found in organic materials or biological light-harvesting complexes.

Krich and his colleagues believe their method is easy to implement for any spectroscopic research group. He highlights the team’s finding hidden structure in the well-known interaction of light with matter.

The study used the “transient absorption” method, with multiple laser powers and a newly-derived formula to systematically separate the effects from just one excitation from those from multiple excitations — up to six — in samples.

The scientists intend to expand the method and use it to analyze energy transport in new photovoltaic materials, which convert light energy into electrical energy.

The study, “Separating single- from multi-particle dynamics in nonlinear spectroscopy” is published in Nature.

P. Malý, J. Lüttig, P. A. Rose, A. Turkin, C. Lambert, J. J. Krich, and T. Brixner, Separating single- from multi-particle dynamics in nonlinear spectroscopy, Nature 616, 280–287 (2023). DOI: 10.1038/s41586-023-05846-7