Experimental demonstration of an ultra-broadband subwavelength resolution probe from microwave to terahertz regime

Abstract

An ultra-broadband subwavelength resolution probe that consists of a Teflon rod and six metallic strips is developed for the near-field imaging system. The slit between two metallic strips maintains quasi-TEM modes, avoiding the problem of low coupling efficiency caused by the cutoff effect. The numerical calculations visualize the process of energy compression into a 0.047λ diameter spot with great field enhancement at the taper apex, and the probe holds subwavelength focusing behavior from 10 GHz to 0.25 THz. Although limited by the fabrication, the resolution of 0.16 and 0.25λ are still experimentally demonstrated at 14 GHz and 0.1 THz. The properties of easy fabrication and no cutoff frequency would lower the threshold of a high-resolution near-field imaging system.

Terahertz Near‐Field Metasurfaces: Amplitude–Phase Combined Steering and Electromagnetostatic Dual‐Field Superfocusing

“…Particularly, the evanescent modes should be considered to overcome the diffraction limit and sharpen the focus spot, as a result of which, one can deliver more near‐field information. In the past decade, some theories and method have been proposed to manipulate the evanescent modes or near‐field electromagnetic (EM) waves, e.g., back‐propagation, Fano resonance, near‐field probe, etc. Note that based on the diffraction integral theory, a previous study proposed a concept of radiationless electromagnetic interference (REI) and achieved a near‐field superfocusing.…”

W-Band Near-Field Microscope

“…Attempts at coupling commercial s-SNOM with an mmW source have invariably failed, because the standard tip is too short (generally between 4-20 µm) to be used to enhance the localized electric field according to standard antenna theory [14], [15], whereas long tips suitable for enhancing mmW field cannot be used with currently available scanning probe microscopy (SPM) for imaging due to inherent configuration limits. To overcome this technical barrier, a variety of aperture based or apertureless near-filed tips/probes were developed, such as low-loss dielectric material sharpened pyramidal tip with a micron-sized plane facet [16], polymethylmethacrylate rectangular tapered probe with metal coating [17], quartz (dielectric) probes excited with a horn antenna [18], Teflon probe azimuthally patterned with several copper strips [19], and microfabricated resonant micro stripline probe [20]. However, none of them was capable of achieving a resolution better than 1 µm in the mmW region.…”

Amplifying Evanescent Waves by Dispersion-Induced Plasmons: Defying the Materials Limitation of the Superlens

“…Imaging with unlimited resolution has been an intriguing dream of scientists for a few centuries. The diffraction limit indicates that the features smaller than half of the working wavelength are carried by evanescent waves which are permanently lost in conventional imaging processes [1,2]. In 2000, the plasmonic effect is demonstrated as an efficient method for breaking the diffraction limit [3], owing to its ability of resonantly amplifying evanescent components [4].…”

“…The diffraction limit indicates that features smaller than half of the operating wavelength are carried by evanescent waves that are permanently lost in conventional imaging processes . With the assistance of an elaborate probe, near-field scanning microscopy can capture the lost information and reach nanometer resolution. − Although this imaging technique has been highly commercialized, it still faces a time-consuming problem and is not suitable for many applications. In 2000, the plasmonic effect was demonstrated as an efficient method for breaking the diffraction limit, due to its ability of resonantly amplifying evanescent components .…”