Nano-optomechanical exploration of the dynamical photothermal response of suspended nanowires to laser-induced thermal waves
Phys. Rev. Applied 25, 064061 – Published 18 June, 2026
DOI: https://doi.org/10.1103/mlnq-flkq
Abstract
Thermal and photothermal effects play an increasing role at the nanoscale due to the general decrease in thermal conductances and the increasing role of interfaces. Here, we present a noncontact optomechanical analysis of the thermal and photothermal properties of suspended nanowires based on pump-probe response measurements: a probe laser measures the nanowire deformations and property changes caused by an intensity-modulated pump laser launching thermal waves propagating along the one-dimensional conductor. The spatiotemporal structure of the thermal waves propagating within the nanowire is imaged by exploiting the temperature-induced optical reflectivity changes of the nanowire. The analysis of the dominant photothermal contributions to the nanowire response in the spectral and spatial domains allows us to reach a quantitative understanding of their photothermal responses and, in particular, to quantify the interfacial contact resistance, detect internal optical Mie resonances, and image absorption inhomogeneities. Finally, we investigate how those thermal waves, through the temperature dependence of the local material stiffness, are responsible for a dynamical modulation of the nanowire vibration frequency in the resolved-sideband regime, providing novel analytical tools to further inspect the structural properties of nano-optomechanical systems with a large signal-to-noise ratio. The precise discrimination between the dominant photothermal mechanisms is enabled here by the measurement and analysis of their temporal transfer functions, in combination with the position and wavelength dependence of their photothermal response. The combination of those local and nonlocal measurements and analytical methods is generic and critical to correctly understand and mitigate the photothermal dynamical backaction processes. They allow us to refine our understanding of this often unwanted source of measurement backaction and help improve the intrinsic sensitivity of those ultrasensitive force probes.
