Broadband, High-Reflectivity Dielectric Mirrors at Wafer Scale: Combining Photonic Crystal and Metasurface Architectures for Advanced Lightsails

Highly ambitious initiatives aspire to propel a miniature spacecraft to a neighboring star within a human generation, leveraging the radiation pressure of lasers for propulsion. One of the main challenges to achieving this enormous feat is to build a meter-scale, ultra-low mass lightsail with broadband reflectivity. In this work, we present the design and fabrication of such a lightsail composed of two distinct dielectric layers and patterned with a photonic crystal structure covering a 4" wafer. We overcome the crucial challenge of achieving broad band reflection of >70% spanning over the full Doppler-shifted laser wavelength range during spacecraft acceleration, in combination with low total mass in the range of a few grams when scaled to meter size. Furthermore, we find new paths to reliably fabricate these sub-wavelength structures over macroscopic areas and then systematically characterize their optical performance, confirming their suitability for future lightsail applications. Our innovative device design and precise nanofabrication approaches represent a significant leap toward interstellar exploration.