Nano-optomechanical exploration of the dynamical photothermal response of suspended nanowires to laser-induced thermal waves

Abstract: Thermal and photothermal effects play an increasing role at the nanoscale due to the general decrease of thermal conductances and to the increasing role of interfaces. Here we present a non-contact 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 1D conductor. The analysis of the dominant photothermal contributions to the nanowires response in the spectral and spatial domains allows in particular to quantify the interfacial contact resistance, to detect its internal optical resonances and to image absorption inhomogeneities. Additionally, by exploiting the temperature-induced optical reflectivity changes of the nanowire, we directly image the spatial structure of the thermal waves propagating within the nanowire. Finally we investigate how those thermal waves 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. Those methods are generic and critical to correctly understand the photothermal dynamical back action processes and improve the intrinsic sensitivity of those ultrasensitive force probes.