Restoring optical forces and torques for passive stabilization of microscopic lightsails

Directed propulsion of lightsails to relativistic speeds by laser radiation pressure demands for passive stabilization, which can be achieved with subwavelength metasurface elements. Our tailored nanophotonic design based on silicon nitride is predicted to give rise to restoring forces and torques upon small perturbations in its dynamics. By measuring the angles and intensities of the diffracted orders, we infer the light-induced pressures on our lightsail prototype. Using Michelson interferometry and laser deflection spectroscopy, we can directly observe the dynamical stability of spring-supported suspended membrane designs. Our results pave the way for lab-scale experiments on optical manipulation of microscopic lightsails.