Controlling the Thermal, Optical and Mechanical Properties of Metasurfaces for Applications Towards Laser Sails

I will discuss how the materials used in metasurface-based laser sails set limits on their thermal stability and the maximum powers that can be used for propulsion. It will be shown that under high optical intensities, non-linear processes and temperature-dependent absorption can create thermal runaway effects in commonly used dielectrics such as silicon. In particular, the combination of two-photon absorption and temperature-dependent bandgap narrowing sets the equilibrium temperature for Si-based metasurfaces in high fluence conditions, and we find the conditions where no equilibrium is achievable. We will also show that the thermal runaway can nucleate near material defects and zodiacal dust, and we demonstrate the time evolution of those processes. Design strategies for mitigating such processes and simultaneously achieving high efficiency will be proposed which include minimizing non-linear materials, and including sacrificial zones on the sail that prevent the spreading of damage. Finally, we will discuss how thermal cooling can be used to impart mechanical stability on the sail, allowing for minimal movement within the drive laser beam.