Research in the Fourkas group lies at the intersection of physical chemistry, optical physics, materials science, nanotechnology, and cellular biophysics. Our research focuses on the use of ultrafast lasers and nonlinear optical techniques to probe, control and fashion condensed matter. Specific areas of interest include:
Nonlinear optical spectroscopy of liquids
Chemical and physical processes in liquids are governed by an intricate interplay between intermolecular structure and dynamics. This interplay becomes all the more important for processes that occur at liquid/solid interfaces, such as heterogeneous catalysis, lubrication, and separations. Our group uses nonlinear optical spectroscopy to study the relationship between the structure and dynamics of bulk liquids, confined liquids, and interfacial liquids. We are developing new spectroscopic tools for probing interface-specific dynamics of liquids, with a current particular interest being understanding the behavior of electrolyte solutions in polar, aprotic organic liquids at liquid/silica interfaces. We are also working on theoretical techniques to extract maximum information from experimental data from nonlinear optical techniques. This work is complemented by molecular dynamics simulations that give direct insights into molecular-level behavior and spectroscopic properties. (See: Natural Sciences 2022, 2, 20210099; Journal of Molecular Liquids 2023, 375, 121315)
Applications of multiphoton absorption
Multiphoton absorption, which is the simultaneous absorption of two or more photons, enables photophysical and photochemical events to be localized in regions with dimensions of 100 nm or less. We harness this phenomenon to perform high-resolution imaging and perform additive and subtractive manufacturing on these distance scales. We also develop methods for determining the order of multiphoton absorption down to the single nanoparticle limit, enabling us to elucidate the mechanisms underlying complex photochemical and photophysical events. (See: Frontiers in Nanotechnology 2022, 4; Journal of Physical Chemistry A 2019, 123, 7314–7322)
Understanding and controlling triplet dynamics
The generation of triplet states is often deleterious to photochemical and photophysical processes, as such states lower fluorescence quantum yields, can serve as bottlenecks to emission, and can even lead to permanent photobleaching. On the other hand, triplet states can be useful in applications such as driving radical reactions and upconverting the wavelength of incident light. We are using a combination of novel experimental methods, kinetic modeling, and rational design to develop new means of controlling triplet dynamics, with eyes towards a wide range of existing and new applications. (See: iScience 2022, 25, 103600; Phys. Chem. Chem Phys. 2022, 24, 28174–28190)
Multicolor lithography
Achieving better resolution in photolithography has typically relied on moving to ever shorter wavelengths of light for exposure. The semiconductor industry, for instance, is pushing forward with technology that is based on the use of extreme ultraviolet (EUV) light, which is challenging to generate, propagate, and manipulate. We are exploring alternative methods of attaining similar resolution that are based on using multiple wavelengths of light in or near the visible range to achieve resolution that may rival that of EUV lithography. This project combines our expertise, and that of our collaborators, in photochemistry, optics, and materials. (See: Optical Materials Express 2019, 9, 3006–3020).
Cellular biophysics
The natural environments of living cells typically feature physical cues, such as collagen fibers, with some dimensions on the order of 100 nm. We use multiphoton fabrication, in combination with other methods, to create substrates with features in this size range. These substrates can be used to study and control the behavior of cells. We and our collaborators have discovered a new mechanism by which cells interaction with topography of this typical dimension: the topography causes selective nucleation and propagation of actin polymerization, in a phenomenon that we have named esotaxis. Esotaxis is broadly conserved across eukaryotic cell types, and offers new opportunities for controlling a wide range of cell behaviors. (See: Proceedings of the National Academy of Sciences USA 2023, 120, e2218906120; Proceedings of the National Academy of Sciences USA 2021, 118, e2021135118).