Characterization of Lightsail Light-Matter Interaction and Nonlinear Dynamics by Microscopic Common-Path Vibrometry*

Dynamic control of macroscopic objects with light has recently became a flourishing research front, largely catalyzed by the ambitious goal of the Breakthrough Starshot Initiative to launch laser-driven lightsails for space exploration. However, for a high-intensity optical drive the heat generated in the lightsail will inevitably affect its dynamics. We have developed a method based on a microscopic common path vibrometer to perform sensitive optical measurements and characterize the light-matter interaction and heat-induced nonlinearity of lightsails. We report the observation of rich nonlinear dynamics in optically pumped tethered silicon nitride lightsails. These include high-order parametric instabilities, injection locking, frequency-mixing and hysteresis induced by Duffing nonlinearity. We find that the spectral positions of the parametric instability tongues deviate from the expected subharmonic <!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>2 style='font-size:12.0pt;mso-ansi-font-size:12.0pt;mso-bidi-font-size:12.0pt;
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