Absorptive Fabry–Pérot Interference in a Metallic Nanostructure

In conventional optics, the Fabry–Pérot (FP) effect is only considered for transparent materials at a macroscopic dimension. Down to the nanometer scale, for absorptive metallic structures, the FP effect has not been directly observed so far. It is unclear whether such a macroscopic effect still holds for a subwavelength metallic nanostructure. Here, we demonstrate the probing of FP interference in a series of nanometer-thick Au films with subwavelength hole arrays. The evidence from both linear and second harmonic generation signals, together with angle-resolved investigations, exhibit features of a FP effect. We also derive an absorptive FP interference equation, which well explains our experimental results. Our results for the first time experimentally confirm the long-persisting hypothesis that the FP effect holds ubiquitously in a metallic nanostructure.