Retrieving Plasmonic Enhancement Factor with Optical Thermometry

The electromagnetic enhancement factor (M) of a plasmonic nanostructure is the crucial quantity that characterizes its enhanced optical effect. Retrieving it experimentally is however stymied by the uncontrollable nuances in nanometer scale and by the lack of a method to gauge the local field. We propose a method to determine the enhancement factor of a plasmonic structure with narrow gaps between adjacent metal nanoparticleshot spotsby exciting the nanoparticles using a light pulse to assess their temperature rise with simultaneously generated inelastic scattering radiation and retrieving the electric field at the gap based on its simple relation with the field inside the nanoparticles. The acquired enhancement factors of Ag nanoparticle arrays with different gaps agree with the values extracted by surface-enhanced Raman scattering and those predicted theoretically. This study demonstrates a general method to retrieve the enhancement factor of the plasmonic systems that are composed of hot spots.