Inverse Design of Diffractive Relativistic Meta‐Sails via Multi‐Objective Optimization

Abstract

Photonic propulsion of light sails using the radiation pressure of an intense laser beam is a promising route to achieve relativistic velocities for deep space exploration. A successful photonic design of such relativistic sails requires efficient acceleration and maintaining stability of the beam‐riding across a Doppler‐broadened propulsion band due to considerable red‐shift of the wavelength in the frame of the moving sail. While efficient acceleration of the sail requires maximizing the optical force along the beam propagation direction, the stability degree of the sail depends on the magnitude of lateral forces in the transverse plane of the beam. This establishes a trade‐off between these two requirements which calls for their synergistic engineering. In this work, an evolutionary multi‐objective optimization technique for the inverse design of diffractive relativistic meta‐sails with a genetic pixelated geometry is adopted. The goal is to identify a set of Pareto optimal solutions which provides the designer with an intuitive understanding of the ultimate trade‐off between acceleration and stability degree of the sail in a vast design space, and allows for a well‐informed decision on the best design given the requirements for the acceleration time and distance as well as the tolerance with respect to mispointings and misalignments.

Multifunctional metasails for self-stabilized beam-riding and optical communication

“…The quantity C ¼ k 1 k 4 + k 2 k 3 describes the coupling between the displacement and rotational degrees of freedom. 20,31,32 A larger magnitude of the coupling between the displacement and rotation yields a lower tolerance of the beam-riding stability with respect to the displacement and rotational offsets, which results in a larger residual motion at the terminal velocity. This is while in case of a positive coupling, slightest perturbations in the position and orientation of the metasail with respect to the beam center can cause the metasail to be expelled from the beam area.…”

“…27,28 More recently, lightsails made of nanophotonic structures and metasurfaces have been shown to not only maximize the acceleration by providing an optimal tradeoff between mass and reectivity, 16,29,30 but also to enable the selfstabilization of beam-riding with at macroscopic geometries. [20][21][22]31,32 These metasails can offer complex wavefront control by relying on phase discontinuities created by their constituent nanoantennas rather than relying on a gradient propagation phase delay in conventional conformal structures. 33 Metasurfaces are also ideal platforms for achieving versatile multifunctional photonic components.…”

“…A common approach to achieve this goal is to use shared aperture interleaved metasurfaces, in which two or multiple sub-arrays are interspersed, each of which is associated with a different phase function. [34][35][36][37][38] Although previous demonstrations of metasails have relied on diffraction or resonant phase tuning to enable wavefront engineering, [20][21][22]31,32 the use of the geometric Pancharatnam-Berry (PB) phase shi seems to be a more natural choice, especially when it comes to a multifunctional design. The use of PB phase not only gives rise to a dispersionless phase discontinuity suitable for the broadband response required across the Doppler-broadened propulsion band for stable beam-riding, but also yields minimal crosstalk between the phase response of the interleaved subarrays in a multifunctional shared aperture platform owing to its non-resonant nature.…”

Multiscale Photonic Emissivity Engineering for Relativistic Lightsail Thermal Regulation

“…Pioneering work on relativistic lightsails has included passive beam-riding stability ,, and maximizing reflectivity on a per-mass basis , in sails composed primarily of Si, SiO 2 , ,,, and Si 3 N 4 . , In these works, the sail’s temperature has largely been a secondary consideration rather than a primary target to be minimized. Here, we propose a method to select sail designs by co-optimizing both their thermal performance and reflectivity, and explore for the first time the use of MoS 2 as a highly reflective material for photonic lightsails.…”

“…We adopt the ultrahigh vacuum (UHV) sublimation temperature T sublimation of the sail materials as a thermal limit. Note that since the UHV sublimation temperature is less than the 1 atm melting temperature selected as the thermal limit in other recent lightsail studies, , this represents a conservative design decision. In our case, we adopted K, which is the lower UHV sublimation point among the two materials used , (see Supporting Information).…”