Direct radiation pressure measurements for lightsail membranes

Creators: Michaeli, Lior¹; Gao, Ramon¹; Kelzenberg, Michael D.¹; Hail, Claudio U.¹; Merkt, Adrien¹; Sader, John E.¹; Atwater, Harry A. (Corresponding)¹

1. California Institute of Technology

Abstract

Ultrathin lightsails propelled by laser radiation pressure to relativistic speeds are currently the most promising route for flyby-based exoplanet exploration. However, there has been a notable lack of experimental characterization of key parameters essential for lightsail propulsion. Here we present a platform for optomechanical characterization and model development of laboratory-based lightsail prototypes. We propose an approach for simultaneous measurement of optical forces and powers based on the multiphysics dynamics induced by the excitation laser beam. By modelling the lightsail with a 50-nm-thick microscopic silicon nitride membrane suspended by compliant springs, we quantify force from off-resonantly driven displacement and power from heating-induced mechanical mode softening. With this approach, we calibrate the measured forces to the driving powers by operating the device as a micromechanical bolometer. We report radiation pressure forces of 70 fN using a collimated beam of 110 W cm−2 and noise-robust common-path interferometry. Moreover, we quantify the effects of incidence angle and spot size on the optical force and explain the non-intuitive trend by edge scattering. As lightsails will also experience lateral forces, we demonstrate measurement of in-plane motion via grating interferometry. Our results provide a framework for comprehensive lightsail characterization and optomechanical manipulation of macroscopic objects by radiation pressure forces.

Copyright and License

Acknowledgement

This work was supported by the Air Force Office of Scientific Research under grant FA2386-18-1-4095 and the Breakthrough Starshot Initiative. L.M. acknowledges support of the Fulbright Israel Postdoctoral Fellowship. We acknowledge helpful discussions with K. Schwab, M. Aellen, C. Went, Y. Kim and A. Michaeli and thank K. Shayegan for lending the piezo-actuated stage.

Data Availability

The data that support the plots within this article and other findings of this study are included in the article and are also available via GitHub at https://github.com/Starshot-Lightsail.

Supplemental Material

Supplementary Information: Supplementary Figs. 1–9 and discussion (Supplementary Notes 1–13).

Contributions

These authors contributed equally: Lior Michaeli, Ramon Gao.

L.M., R.G. and H.A.A. conceived the project. L.M. built the common-path interferometer. R.G. fabricated the devices. L.M. and R.G. built the optical setup, conducted the measurements and performed the data analysis. M.D.K. assisted with the feedback stabilization of the AOM. M.D.K. and C.U.H. provided inputs on the angle-dependent measurements. M.D.K. and A.M. designed the vacuum chamber and line with inputs from R.G. J.E.S. offered guidance with the device stiffness measurement and provided theoretical insights. L.M. and R.G. wrote the paper with inputs from all authors. H.A.A. supervised the project.

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