Self‐Focusing Non‐Diffracting Special Beam in Hyperbolic Media

Abstract The field of non‐diffracting special beams, distinguished by their non‐diffracting characteristics during propagation in free space, has experienced substantial progress over the last decade. However, the exploration of special beams has been predominantly focused on isotropic background media, with limited attention given to their behavior in anisotropic backgrounds, such as elliptical or hyperbolic media. In this study, the characteristics of non‐diffracting wave propagation in anisotropic media is investigated, specifically the hyperbolic media by means of using α‐MoO ₃ , a van der Waals (vdW) crystal that supports in‐plane hyperbolic surface phonon polariton in the mid‐infrared (MIR) spectrum as the platform. Specifically, it is demonstrated that the special beams can be constructed under various isofrequency contours by the application of coordinate transformation scheme. More intriguingly, it is revealed that the special beam propagation in hyperbolic media can exhibit the distinctive feature of self‐focusing. This investigation provides new perspectives for the understanding of special beam formations and introduces new possibilities for complex beam manipulation in extreme anisotropic environments within the MIR regime.