An alternative scheme is to create 3D metal tip with patterned metallic pyramids obtained via silicon template stripping. The efficiency is significantly enhanced to the level of 0.1%-1%, and the background signal is greatly suppressed and SNR level is increased a lot, opening better opportunities in nanospectroscopy 22, 23. This grating can help to transform the incident far-field laser beam into resonant generation of SPPs traveling over more than 10 µm to the tip apex and converging to an intense radiative local light spot with size of few tens of nanometers. introduced a one-dimensional (1D) grating on the shaft of a sharp conical metal taper with a tip radius of few tens of nanometers. Two major problems exist for apertureless s-SNOM, one is the weak transmission efficiency of signal light for use, the other is the strong background signal and thus bad signal-to-noise ratio (SNR) level. Besides, the resolution is limited due to aperture size, at about 50-100 nm. With a balance of luminous flux and aperture size, these deliberately designed probes still have very low optical throughput, resulting in weak signal light in use. integrated a 100 nm nanoaperture surrounded by a circular through grating that resembles a plasmonic lens on the metal coating of a conic SNOM tip 21. adopted complex-shape aperture such as H-shaped and bowtie-shaped aperture other than regular circular aperture and the transmission efficiency could increase by one order of magnitude 20. In regard to metal-coated tapered fiber tip in a-SNOM, Xu et al. Many schemes have been developed and adopted to relieve the difficulty of very low transmission efficiency intrinsic with classical a-SNOM and s-SNOM instruments. 1b, can have high resolution by reducing the tip apex size, but suffers both low throughput and low signal contrast. 1a, a-SNOM can have high resolution and high contrast by reducing the aperture size, but suffers low throughput, while the s-SNOM, as schematically illustrated in Fig. The classical SNOM techniques can be classified into the “aperture SNOM” (a-SNOM) 3, 4, 5, 6, 7, 8 and “aptertureless or scattering SNOM” (s-SNOM) 9, 12, 13, 14, 15, 16, 17, 18, 19 categories. In early 1980s, the great success of scanning tunneling microscopy (STM) and atomic force microscopy (AFM) stimulated the invention of SNOM 5, 6, 7, 8, 9, and since then a wide variety of SNOM instruments have been developed, advanced, and placed into applications for basic sciences 10, 11. Among different means of super-resolution optical imaging schemes and technologies, scanning near-field optical microscopy (SNOM) is a purely optical technique that can effectively lift the diffraction limit of resolution 1, 2, 3, 4. History tells us that this is never an easy task. Meanwhile, it is also highly desired that the advancement in the imaging resolution of nanoscopy is not in the price of severe degradation in many other advantages of conventional optical microscopy. In recent decades there has been increasing demand to lift this limitation and push the resolution down to nanometer scale, thus effectively upgrading optical microscopy into optical nanoscopy. But it also determines the spatial resolution of optical imaging to be micrometer scale at best, thanks to the diffraction effect of light wave, and this becomes the biggest disadvantage of conventional optical microscopy. Optical microscopy offers a bridge connecting macroscopic and microscopic world through imaging, spectroscopy, and other means in space-time domain. This high-resolution, high throughput, and high contrast SNOM would open up a new frontier of high spatial-temporal resolution detecting, imaging, and monitoring of single-molecule physical, chemical, and biological systems, and deepen our understanding of their basic science in the single-molecule level. Numerical simulations and optical measurements show that this specially designed and fabricated tip has 10% transmission efficiency, ~ 5 nm spatial resolution, 20 dB signal-to-noise ratio, and 7000 pixels per second fast scanning speed. Here we present design and 3D printing of a fiber-bound polymer-core/gold-shell spiral-grating conical tip that allows for coupling the inner incident optical signal to the outer surface plasmon polariton with high efficiency, which then adiabatically transport, squeeze, and interfere constructively at the tip apex to form a plasmonic superfocusing spot with tiny size and high brightness. Scanning near-field optical microscopy (SNOM) offers a means to reach a fine spatial resolution down to ~ 10 nm, but unfortunately suffers from low transmission efficiency of optical signal.

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