Photonic Metasurfaces as Relativistic Light Sails for Doppler‐Broadened Stable Beam‐Riding and Radiative Cooling
Mohammad Mahdi Salary, Hossein Mosallaei
Abstract
Abstract In this work, an all‐dielectric photonic metasurface with a flat macroscopic geometry is shown to provide a viable solution toward realization of a relativistic light sail driven by radiation pressure from high‐power lasers offering passive beam‐riding stability, efficient acceleration, and radiative cooling is demonstrated. A critical challenge that is addressed is sustaining acceleration and stability over the Doppler‐broadened propulsion band which is crucial for achieving relativistic velocities and requires the metasurface to maintain a high reflectivity and wide phase coverage over a broad bandwidth. For this purpose, a zero‐contrast dielectric metasurface consisting of a graded pattern of c‐Si nanodisks connected by a thin matched sublayer on top of a thin silica layer, featuring an average areal mass density of 0.54 g m −2 is used. The nanostructured silicon layer is mainly responsible for efficient acceleration and self‐stabilization of beam‐riding while the thin silica layer enhances the thermal emissivity to preserve the integrity of meta‐sail under intense illumination power via radiative cooling. The role of phase gradient, nanocraft center of mass, Doppler shift, and chromatic dispersion on the interplay between stability and acceleration of the meta‐sail is identified. Moreover, motion trajectory and local steady‐state temperature of the meta‐sail during acceleration are estimated.