摘要： Engineering the photothermal effect in plasmonic materials is of paramount importance for many applications such as cancer therapy, chemical synthesis, cold catalysis and more recently for metasurfaces. Evaluation of plasmonic heating at the nanoscale is challenging and generally requires sophisticated equipments and/or temperature-sensitive probes such as fluorescent molecules or materials. Here we propose to use water vapor as probe to evaluate the local heating around plasmonic nanoparticles. We demonstrated the concept for the case of a plasmonic colloidal film composed by a bi-modal nanoporosity. In particular we exploit the thermal and light water liquid-vapor phase transitions taking place into the nanoporous medium that can be triggered by external stimulus such as heating or irradiation to obtain structural and optical variations in the films. Estimation of the local temperature was then obtained by using spectroscopic ellipsometry acquired by a multimodal chamber. More generally, this method offer a simple and general approach to determine local temperature that only requires a nanoporous material and water vapor, such as environmental humidity. In addition this approach can be further generalized to other materials, vapor molecules or optical technique.