, Volume 8, Issue 2, pp 715-722
Date: 22 Dec 2012

Sensing Nanometer Depth of Focused Optical Fields with Scanning Surface Plasmon Microscopy

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Evanescent wave imaging has been developed in the past decades for discriminating sub-micronic structures confined on a planar surface from bulk medium. However, this imaging method assumes a correct orientation of the objective lens versus the normal of the sample plane (null tilt angle) for a uniform evanescent illumination of the sample. Here, we propose to use the \(V(Z)\) response of a heterodyne scanning microscope coupled to a high numerical aperture lens to compensate the tilt, scanning images in three dimensions. This method can be used in standard glass to dielectric reflection regime or coupled to surface plasmon resonance. We show that in the second case, we can afford tilt angle corrections better than 10 \(^{-4}\) radian. As an illustration, this method is applied to a patterned surface with nanometer-squared silica islets and to adsorbed nanoparticles.