Grant: Alliance Grants

Spectroscopy is possibly the most common tool for learning about materials. By shining light on them to see which wavelengths are absorbed, we gain insight into the quantum states that make up the molecules or materials studied. Spectroscopy is usually performed with weak incident light pulses, so each molecule absorbs either zero or one photons. As the pulse intensities increase, some molecules absorb two (or more) photons, enabling study of the interaction between the excitations. But such experiments are often hard to interpret, as they also contain responses from molecules that absorbed only one photon. Development of solar cells, functional materials, and quantum technologies requires understanding what happens when these systems have multiple excitations. This Alliance International Collaboration between the University of Ottawa and the University of Würzburg, in Germany, will develop and apply new theoretical and experimental methods to give better control of multi-excitation states in several forms of spectroscopy. Experimental spectroscopic signals contain a combination of signals resulting from one, two, three, or more interactions of the system with light. We will develop new methods to systematically separate those signals by combining spectroscopies measured with different pulse intensities, without detailed knowledge of the properties of the system under study. We will show how these separated signals provide new insight and understanding of multi-particle interactions in a variety of material and molecular systems. These new techniques will enable characterization and development of new optoelectronic materials, such as LEDs and solar cells, aiding Canada's status as a high-tech science and engineering hub.