Common-path confocal interferometric surface plasmon microscopy

Surface plasmon (SPs) microscopy can measure local changes of refractive index on the nano scale and has been successfully applied in biomedical or semiconductor material fields. Here, we propose and develop a novel common-path confocal interferometric SPs microscopy. This technique delivers quantitative high spatial resolution sensitive to refractive index and offers the advantages of simplicitye, low cost, low environmental requirements, and high signal-to-noise ratio. The so-called V(z) effect is the period oscillation by the relative phase between the reference and the SPs signal and obtained by scanning the sample along the optical axis (z direction) with a Piezo-electric stage. We demonstrate that the image contrast can be controlled by varying the sample defocus without substantially degrading spatial resolution. We also verify the technique theoretically and experimentally.