Controlling photothermal forces and backaction in nano-optomechanical resonators through strain engineering

TL;DR

This paper demonstrates how nanoscale structural design can control photothermal forces in nano-optomechanical systems, enabling tailored backaction effects for improved device performance.

Contribution

It introduces a method to engineer the sign and magnitude of photothermal forces via structural design, validated experimentally in a nanobeam zipper cavity.

Findings

Geometry change controls photothermal force magnitude and sign

Backaction effects can be minimized or maximized through design

Experimental validation in nanobeam zipper cavity

Abstract

In micro- and nanoscale optomechanical systems, radiation pressure interactions are often complemented or impeded by photothermal forces arising from thermal strain induced by optical heating. We show that the sign and magnitude of the photothermal force can be engineered through deterministic nanoscale structural design, by considering the overlap of temperature and modal strain profiles. We demonstrate this capability experimentally in a specific system: a nanobeam zipper cavity by changing the geometry of its supporting tethers. A single design parameter, corresponding to a nanoscale geometry change, controls the magnitude of the photothermal backaction and even its sign. These insights will allow engineering the combined photothermal and radiation pressure forces in nano-optomechanical systems, such that backaction-induced linewidth variations are deterministically minimized if needed, or maximized for applications that require cooling or amplification at specific laser detuning.