Abstract

Surface plasmon resonance (SPR) has found wide applications in sensing down to molecular level due to its extreme sensitivity to change of dielectric properties. An unavoidable effect in SPR is surface deformation (thermal bump) due to local heating by incident laser light used in SPR. In addition, change in the reflection phase from the metal film used in SPR could also contribute to the SPR signal, and thus proper handling of the SPR signal is very important in order to broaden the potential applications of SPR. Here a simple Fabry Perot (FP) interference technique for measuring, simultaneously, the thermal bump height as well as the reflection phase shift of gold film used in SPR is reported. The shift of the FP signal is dominated by the effect of the thermal bump while it is small for the effect of the reflection phase shift due to the change of dielectric property of the metal. To support the experimental results, model simulations for the SPR system are performed and obtained good agreement with the experiment. The effect of the thermal bump on the resonance of surface plasmon is also investigated and a polarization-dependent reflection phase shift for the probe beam is observed in SPR by adjusting the thermal effect for different pumping polarization. As both amplitude and phase can be measured, our method could lead to better characterization of SPR and can also be applied to the study of active metasurfaces under external excitation.