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Description
Light incident upon matter exerts a radiation pressure force, a phenomenon that enables applications such as optical tweezers and laser cooling. Typically, the matter that is moved by radiation pressure is treated as a rigid body, yet new physics and applications emerge when considering radiation pressure on elastic bodies. The simplest interaction involves pulses of laser light reflected off an elastic medium driving compression waves inside, which however does not couple radiation pressure to the resultant elastic waves. In Brillouin scattering, optical fields generate radiation pressure that couples to acoustic waves in a waveguide, but the interaction is obfuscated by many intermediate, coupled nonlinear effects.
In contrast, we report here a direct, linear coupling between radiation pressure and elastic waves in matter. It arises because the magnitude of radiation pressure on a body depends on the body's optical-scattering properties, which can change drastically when elastic waves pass through the body. The interaction breaks reciprocity in the system, causing elastic waves to grow exponentially in space--this is the non-Hermitian skin effect (NHSE) [1]. We show that the growth rate can be enhanced by orders of magnitude to measurable scales in membranes consisting of optically dispersive diffraction gratings. Our radiation-pressure system is the first proposal of a mechanical NHSE that does not require active controllers [2] nor gain/loss materials [3]. An application of our results is interstellar lightsails, which are thin and therefore flexible membranes that are accelerated by radiation pressure from high-power lasers to near-relativistic speeds.
[1] S. Yao and Z. Wang, Physical Review Letters 121(8), 086803 (2018)
[2] M. Brandenbourger et al., Nature Communications 10(1), 4608 (2019)
[3] X. Zhang et al., Nature Communications 12(1), 5377 (2021)
| I am the presenting author | Yes |
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