Multifrequency Excitation and Detection Scheme in Apertureless Scattering Near-field Scanning Optical Microscopy

We introduce a novel excitation and detection scheme in near-field optical microscopy, based on the bi-modal excitation of an AFM tip and a multifrequency detection scheme in SNOM (MF-SNOM). Using this method, we experimentally demonstrate enhanced sensitivity, implying improved spatial resolution in optical measurements. This model predicts a set of experimental parameters relevant for the suppression of optical background in the detected signal. We observe that in the multimodal excitation method, the solution space for these parameters spreads over a two-dimensional plane, thus allowing further degrees of freedom in near-field measurements. We experimentally showed [1] that this scheme allows for a two-fold enhanced sensitivity in the measurement of a near field signal as a function of tip-sample distance. Our measurements of 500nm gold nanorods, with resolved lateral optical features of the order of 7nm, imply that this enhanced sensitivity leads to an improved resolution in the x-y plane.

[1] H. Greener, M. Mrejen, U. Arieli, and H. Suchowski, “Multifrequency excitation and detection scheme in apertureless scattering near-field scanning optical microscopy,” Opt. Lett. 42, 16 (2017).