Nonlinear optics is a subfield of physics studying the interaction between matter and intense light, typically laser light. Nonlinear optical phenomena can change the properties of light, such as its wavelength. These modifications have allowed the development of numerous laser devices, including wavelength-tunable and pulsed lasers.
Although nonlinear processes result in drastic changes in the properties of the interacting light, they are, by their nature, extremely inefficient. Conventionally, this issue is solved by utilizing phase-matching schemes and optical resonators. Phase matching is a concept which can be used for coherent build-up of nonlinear responses during propagation inside a nonlinear optical material. Optical resonators are systems into which light waves can be coupled, which boosts optical processes occurring inside the resonator. Traditional optical resonators consist of two or more high-quality mirrors.
“The traditional components relying on phase-matching schemes and optical resonators work like a dream. Unfortunately, such components are incompatible with modern microphotonics,” Timo Stolt says.
Metamaterials enable flat photonic components
In his dissertation, Stolt investigates nonlinear optical metamaterials, which could enable nonlinear optics in microphotonics. Metamaterials are artificial structures consisting of nanoscale building blocks. So far, metamaterials have allowed the miniaturization of numerous optical components, including lenses, polarizers, and optical filters.
Stolt’s doctoral research focuses on plasmonic metamaterials consisting of metal nanoparticles arranged in periodic lattices. Such structures exhibit resonances that can be used to store light energy, and consequently, boost light-matter interaction. Stolt utilized this so-called resonant enhancement when developing metamaterials with tunable and broadband nonlinear responses. Furthermore, he also utilized the phase-control aspect of these resonances and demonstrated phase matching in structures consisting of stacked nanoparticle arrays.
“In principle, resonant metamaterials are extremely thin optical resonators with additional functionalities, such as phase matching of nonlinear processes. In other words, we brought well-known enhancement techniques to the microscopic scale,” Stolt explains.
Overall, the results of Stolt’s work could pave the way toward tunable, efficient, and multifunctional nonlinear metasurface components. Such components could be utilized, for example, in ultraviolet laser sources, photon pair sources, or metasurface-based holography.
Timo Stolt, born and raised in Tuusula, is currently working in the Nonlinear Optics Group at Tampere University.
Public defence on Friday 22 March
The doctoral dissertation of M.Sc. (Tech.) Timo Stolt in the field of physics titled Nonlinear Optics using Resonant Metamaterials will be publicly examined at the Faculty of Engineering and Natural Sciences at Tampere University at 12 o’clock on Friday 22nd of March 2024 at Hervanta campus, Tietotalo, auditorium TB109 (Korkeakoulunkatu 1, Tampere). The Opponent will be Professor Rupert Oulton from Imperial College London. The Custos will be Professor Martti Kauranen from the Faculty of Engineering and Natural Sciences.