Near-Field Scanning Optical Microscope Combined with Digital Holography for Three-Dimensional Electromagnetic Field Reconstruction

Abstract

Near-fieldHolographydigital scanningNear-fields optical microscopy (NSOM) hasMicroscopyoptical provenMicroscopyscanning to be a very powerful imaging technique that allows overcoming the diffraction limitDiffraction limit and obtaining information on a scale much smaller than what can be achieved by classical optical imaging techniques. This is achieved using nanosized probesProbe that are placed in close proximity to the sample surface, and thus allow the detection of evanescent wavesEvanescent wave that contain important information about the properties of the sample on a subwavelength scale. In particular, some apertureAperture-basedProbeprobesAperture probe use aNanometer nanometer-sized hole to locally illuminate the sample. The far-field radiation of such probesProbe is essential to their imaging properties, but cannot be easily estimated since it highly depends on the environment with which it interacts. In this chapter, we tackle this problem by introducing a microscopy method based on full-fieldFull field off-axisHolographyoff-axis digitalHolography holographyHolographydigital thatOff-axis holography allows us to study in details the three-dimensionalImagingthree-dimensional electromagnetic field scattered by a NSOM probeProbe in different environments. We start by describing the NSOM and holography techniques independently, and continue by highlighting the advantage of combining both methods. We present a comparative study of the reconstructed light from a NSOM tip located in free space or coupled to transparentTransparent media and plasmonic mediaPlasmonic media. While far-field methodsFar-field methods, such as back-focal planeBack-focal plane imaging, can be used to infer the directionality of angular radiation patternsAngular radiation pattern, the advantage of our technique is that a single hologramHolograms contains information on both the amplitudeAmplitude and phase of the scattered light, allowing to reverse numerically the propagation of the electromagnetic field toward the source. We also presentFinite-difference time-domain method Finite-Difference Time-DomainFinite-Difference Time-Domain (FDTD) simulations (FDTD) simulations to modelModel the radiation of the NSOM tip as a superposition of a magnetic and anElectric dipole electric dipoleDipole. We finally propose some promising applications that could be performed with this combined NSOM-holographyHolography technique.