Negative Reflection of Nanoscale-Confined Hyperbolic Polaritons

In this chapter, we discuss the direct visualization of nanoscale-confined polaritons negatively reflecting on subwavelength mirrors fabricated in the low-loss van der Waals crystal \(\alpha \text{-MoO}_{3}\) . Our near-field nanoimaging results unveil unconventional and broad tunability of both the polaritonic wavelength and direction of propagation upon negative reflection. On the basis of these findings, we introduce a novel device in nano-optics: a hyperbolic nanoresonator, making possible to reflect hyperbolic polaritons with different momenta back to a common point source, enhancing the intensity. These results pave way to realize nanophotonics in low-loss natural media, providing an efficient route to control nanolight, key for future on-chip optical nanotechnologies. The near-field experiments reported in this chapter were carried out in collaboration with Dr. Jiahua Duan (University of Oviedo, Spain). Sample fabrication was performed mainly by Javier Taboada Gutiérrez (University of Oviedo, Spain), Dr. Elizaveta Nikulina (CIC nanoGUNE; Spain) and Dr. Qingdong Ou (Monash University, Australia). The results were published in “Negative reflection of nanoscale-confined polaritons in a low-loss natural medium” by Gonzalo Álvarez-Pérez, Jiahua Duan et al., in Science Advances 8 (29), eabp8486 (2022).