The mid-infrared spectral region holds significant potential for applications in energy harvesting and waste-heat recovery, radiative cooling, spectroscopy, sensing, thermal camouflage and night vision, among others. Conventional approaches to controlling mid-infrared (mid-IR) radiation with metamaterials and metasurfaces often rely on intricate fabrication methods. Commercial components for mid-IR photonics rely on materials that limit their scalability and accessibility. In this thesis, we explore how van der Waals (vdW) heterostructures, with their intrinsically anisotropic optical properties and deeply subwavelength thicknesses, enable unprecedented manipulation of thermal emission in terms of directionality, polarization, and chirality.

We first introduce a straightforward far-field method to extract the complex dielectric function of microscopic exfoliated flakes, facilitating accurate characterization of highly dispersive polar materials without sophisticated near-field instrumentation. We demonstrate how ultrathin flakes of α-molybdenum trioxide (α-MoO₃) can serve as deeply subwavelength phase retarders in the mid-IR, enabling efficient polarization control at spectral regions inaccessible to conventional bulk optical components. Moreover, we show that by simply twisting two anisotropic flakes, intrinsic mid-IR chirality can be engineered, resulting in circular dichroism in both absorption and thermal emission, effectively transforming inherently incoherent blackbody radiation into circularly polarized emission.

Finally, we develop structures based on anisotropic dielectric spacers within Salisbury screen configurations, enabling simultaneous control over the azimuthal and zenithal angles of emitted thermal radiation. Through analytical and numerical analysis, clear design principles are derived and validated using realistic materials. The results presented here establish vdW materials and their heterostructures as versatile platforms for advanced mid-infrared photonic applications, significantly enhancing our capability to precisely tailor thermal radiation across a broad range of practical applications.

Monday September 29, 14:00 h. ICFO Auditorium
Thesis Director: Prof. Dr. Georgia Papadakis