Optical Characterization of Silicon Nitride Metagrating-Based Lightsails for Self-Stabilization

We report ultrathin photonic metagratings where anisotropic scattering is designed to achieve self-stabilizing dynamics in a collimated beam of laser light. Stability necessitates a delicate balance between all scattered orders of light, which we demonstrate in a monolithic material platform suited for efficient propulsion in space. Our suspended structures are fabricated in silicon nitride membranes, which is a promising lightsail material candidate due to its wafer-level scalability and favorable mechanical and optical properties. Lightsail prototype designs are optically characterized by angle-resolved photocurrent measurements of the intensities and angles of the asymmetric ±1 diffraction orders. We infer the optically induced forces and torques from refracted and reflected light measurements and show that these are restoring along one axis by providing them as input functions to numerical simulations of lightsail dynamics. Our experimental results represent a first step toward full dynamical verification of realistic lightsail designs and pave the way for realization of stable beam-riding lightsails composed of ultrathin dielectric membranes.