Spatial and Temporal Nanoscale Plasmonic Heating Quantified by Thermoreflectance

The field of thermoplasmonics has thrived in the past decades because it uniquely provides remotely controllable nanometer-scale heat sources that have augmented numerous technologies. Despite the extensive studies on steady-state plasmonic heating, the dynamic behavior of the plasmonic heaters in the nanosecond regime has remained largely unexplored, yet such a time scale is indeed essential for a broad range of applications such as photocatalysis, optical modulators, and detectors. Here, we use two distinct techniques based on the temperature-dependent surface reflectivity of materials, optical thermoreflectance imaging (OTI) and time-domain thermoreflectance (TDTR), to comprehensively investigate plasmonic heating in both spatial and temporal domains. Specifically, OTI enables the rapid visualization of plasmonic heating with sub-micron resolution, outperforming a standard thermal camera, and allows us to establish the connection between the optical absorptance and heating efficiency as well as to anal...