Theoretical and experimental investigation of the plasmonic probe The diffraction limit does not permit us to reveal information from dimensions smaller than roughly one half of the wavelength. Hence it was traditionally impossible to optically interact selectively with nanoscale features. However with the increasing trend towards nanoscience and nanotechnology nano optics science emerged. A central goal of nano optics is to extend optical techniques to length scales beyond the diffraction limit. In recent years several new approaches have been developed to overcome this limitation. Tip enhanced near field microscopy techniques such as TERS and PiFM are among the innovations built around an AFM system. In this work first an algorithm for batch processing of the measured AFM data is introduced and utilized to analyze the height distribution of the inactivated SARS CoV 2 samples. In the next chapter plasmonic probes as the crucial components of any near field optical microscopy techniques are modeled and investigated. Here complex and realistic particle shapes are used to analyze particle based probes’ near and far field behavior. It has been shown that only the frontmost particle is decisive for the near field signal. On the other hand the rest of nanoparticles enhance the scattering intensity. Apart from the optical responses the mechanical properties of tips are also modeled because higher harmonics of the tip’s oscillations are the foundation of new patents such as torsional force microscopy and photo induced force microscopy (PiFM). In the last chapter the PiFM is introduced and employed in various applications i.e. plasmonic probe’s quality field mapping and optical response of the plasmonic NPs.