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Functional extreme nonlinear nanomaterials

Periodic Reporting for period 2 - NONLINMAT (Functional extreme nonlinear nanomaterials)

Reporting period: 2019-02-01 to 2020-07-31

Metasurfaces that mimic artificial order in the matter have recently opened an exciting gateway to reach unprecedented properties and functionality for the modification of light propagation. The artificial “atoms” and “molecules” of the metasurface can be tailored in shape and size, the lattice constant and inter-atomic interaction can be precisely tuned. Furthermore, using symmetry and polarization state properties topological Berry phase effects can greatly enhance the functionality of such surfaces.
With this project, we explore the revolutionary physics of nonlinear optical Berry phase metasurfaces, covering nonlinear optical frequency generation and wave dispersion engineering as well as real-time reconfiguration of nonlinear optical properties. Novel unique nonlinear optical properties of metasurfaces that arise from their specific topological configurations open up exciting new venues for device development in the fields of all-optical data processing, optical meta-nanocircuits, phase conjugating perfect mirrors, and background-free nonlinear holography. We investigate the possibilities of strongly enhanced nonlinear light-matter interaction and novel nonlinear optical processes that are based on nonlinear topological Berry phase effects coupled to inter- and intersubband transitions of novel 2D materials. Single layers of transition metal dichalcogenides will allow reconfigurable nonlinear optical properties by changing the valley band transitions.
The project covers the development of innovative fabrication technologies, fundamental investigations of the origin and the design of effective nonlinearities with controlled phase, experimental characterizations, as well as device development. The findings of the project based on highly nonlinear reconfigurable metasurfaces based on symmetry and topological effects will impact interdisciplinary research fields including condensed matter physics, optoelectronics, and biophotonics. Fast optical switches and frequency converter in miniaturized and integrated systems for quantum information technology might benefit from the small footprint and the design freedom of metasurfaces.
During the first half of the project, we focused our research on the development of nonlinear metasurfaces for functional elements, like nonlinear holograms. Within our studies, we investigated the possibilities to increase the information capacity of metasurface holograms consisting of ultrathin layers of nanostructured materials. Therefore, new design algorithms and suitable structure design of the unit-cells were developed. Such algorithms are necessary for obtaining high-quality holographic images and information recovery from the metasurfaces when they are illuminated by particular light states.
Furthermore, we studied the performance of plasmonic, hybrid, and purely dielectric metasurfaces for nonlinear light conversion. In such a way, the illuminating light at a particular frequency can be converted to two or three times the frequency, allowing to go from near-infrared light to the visible. For that, we developed a concept that can tailor the spatial phase of this conversion process, which is mandatory for nonlinear beam shaping and holography. First, metasurfaces were fabricated and tested for their optical performance. With some impressive experiments, we were able to show for the first time some imaging of objects by a nonlinear metalens, which led to the conclusion that the traditional lens equation for linear ray optics can be modified to include nonlinear optical effects.
Another part of the project studied the potential of active materials for dynamically tunable or switchable optical metasurface holograms. Such metasurfaces can reveal different information by externally stimulated by some trigger. We showed that chemical processes, as well as temperature, can be used to obtain such behavior when particular materials are combined.
We are expecting that we can improve the efficiency of the nonlinear metasurface with some new techniques several orders of magnitude compared to our previously shown structures. This would be very important for developing some application and use these metasurfaces outside the research lab. Furthermore, we are targeting the development of optical trapping devices that can be used in integrated on-chip biophotonic applications.
Switchable nonlinear hybrid metamaterial