Design of Near-field Probes in Terahertz and Optical Band

One of the fundamental limitations in terahertz and optical imaging, is the spatial resolution limited to half of the wavelength which is caused by the wave nature of light, and is known as the Rayleigh diffraction limit. Such resolution is insufficient for the study of many objects and phenomena including biological cells, mobile carriers in semiconductor nano-devices, as well as heat transfer and electromagnetic interference phenomena in nano-electronic circuits. In recent decades, some efforts have been made to introduce and develop techniques to overcome this limitation, including methods based on using near-field and detecting evanescent waves. In most of the proposed methods, a near-field probe is used to concentrate the field near the sample, and to couple the near-field (evanescent field) into radiation or propagating wave. In this paper, with an emphasis on the fundamental aspects of the near-field technique, we review, investigate, and work on a harmonized set of basic definitions associated with near-field imaging. The diffraction limit and its theoretical origin, the applications of near-field imaging, possibility to achieve sub-wavelength resolution in accordance with Heisenberg uncertainty principle have been explored. Finally, by describing the design process of three near-field imaging probes, their capabilities are investigated.