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Grating-assisted coupling enhancing plasmonic tip nanofocusing illuminated via radial vector beam
摘要： Tip-enhanced Raman spectroscopy (TERS) is a very useful method to achieve label-free and super-resolution imaging, and the plasmonic tip nanofocusing plays a decisive role for TERS performance. Here, we present a method to enhance the nanofocusing characteristic of a plasmonic tip integrated in a grating near the tip apex. Simulation results show that the grating near the tip apex can significantly improve the electric field intensity of the nanofocusing field compared with a conventional bare tip, under axial excitation of a tightly focused radial vector beam. The electric field enhancement characteristic is quantified in relation with the groove number of grating, excitation wavelength, period of grating, and numerical aperture of the micro-objective (MO). These simulation results could be a good reference to fabricate a plasmonic tip for TERS applications, which is an effective way to promote the development of tip-enhanced near-field optical microscopy.
关键词： tip-enhanced Raman spectroscopy,radial vector beam,plasmonic tip nanofocusing,surface plasmon polariton
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Towards Near-Field Coupling of Surface Plasmon Polaritons across Few-Nanometer Gaps between two Laterally Tapered Gold Waveguides
摘要： Nanofocusing of light in combination with an efficient energy transfer of metallic nanostructures is a key task towards ultrafast, all-optical switching on the nanoscale. A possible realization of such a device is based on two tapered plasmonic nanostructures separated by a few-nanometer gap, in which information transport is controlled via strong coupling of the electromagnetic near-field and excitonic molecules in the gap region of the waveguides. The fabrication of such mesoscopic nanostructures that can concentrate free-propagating light to few-nanometers dimensions remains challenging due to the desired nanometer precision in the gap region. Here, we report on the fabrication of a plasmonic nanostructures consisting of a pair of both striped and tapered waveguides in 200 nm thick Au films with gap sizes and radii of curvature down to 11 nm using a Focused Ion Beam-based “Sketch and Peel” lithography process. Curved focused-ion beam written gratings in the waveguides enable the in- and out-coupling and focusing of surface plasmon polaritons into the nanostructure. The propagation of these SPPs is afterwards monitored using far-field confocal microscopy. We find a relatively constant transmission of light for large gap sizes, accompanied by a drastically increase for gap sizes below 20 nm. This increase for small gap sizes can be approximated best by fitting an exponential decay with a decay length of 8 nm suggesting a significant energy transport through near-field coupling of the two waveguides. These experimental findings are in accordance to finite element method and finite difference time domain calculations that show a strong localization of the electric field in the gap region of the two waveguides. The profound electric field strength and the spatial confinement of the electric fields suggest such plasmonic waveguides as prototypical structures for probing the strong coupling between propagating surface plasmon polaritons in adjacent, however separated plasmonic waveguides on one hand and between SPP waves and single quantum emitters that are placed in the gap region of the waveguides on the other hand. The realization of such coupling could enable the ultrafast, remote switching on the nanoscale.
关键词： ultrafast switching,nanofocusing,near-field coupling,surface plasmon polaritons,plasmonic nanostructures
更新于2025-09-16 10:30:52
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Round-tower plasmonic optical microfiber tip for nanofocusing with a high field enhancement
摘要： A round-tower (RT) plasmonic tip based on an optical microfiber for nanofocusing is proposed. Its operation principle is systematically analyzed by theoretical methods. Four operation regions of the theoretical model of the plasmonic tip are identified for the first time in this study. In addition, the near-field performances of the plasmonic optical microfiber tip are investigated by a finite-element simulation. The results reveal that the field enhancement at the tip apex can be improved by adjusting the slope angle of its surface plasmon polariton region. Remarkably, the proposed RT plasmonic tip can achieve a significantly enhanced field at the tip apex and simultaneously focus the optical spot to a few nanometers. The characteristics of superfocused optical spot and ultrahigh field enhancement are promising for applications in scanning near-field optical microscopy, optical recording, nanolithography, and biosensing.
关键词： Plasmonic tip,Optical microfiber,Finite-element simulation,Nanofocusing
更新于2025-09-12 10:27:22
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Plasmonic Nanolenses Produced by Cylindrical Vector Beam Printing for Sensing Applications
摘要： Interaction of complex-shaped light fields with specially designed plasmonic nanostructures gives rise to various intriguing optical phenomena like nanofocusing of surface waves, enhanced nonlinear optical response and appearance of specific low-loss modes, which can not be excited with ordinary Gaussian-shaped beams. Related complex-shaped nanostructures are commonly fabricated using rather expensive and time-consuming electron- and ion-beam lithography techniques limiting real-life applicability of such an approach. In this respect, plasmonic nanostructures designed to benefit from their excitation with complex-shaped light fields, as well as high-performing techniques allowing inexpensive and flexible fabrication of such structures, are of great demand for various applications. Here, we demonstrate a simple direct maskless laser-based approach for fabrication of back-reflector-coupled plasmonic nanorings arrays. The approach is based on delicate ablation of an upper metal film of a metal-insulator-metal (MIM) sandwich with donut-shaped laser pulses followed by argon ion-beam polishing. After being excited with a radially polarized beam, the MIM configuration of the nanorings permitted to realize efficient nanofocusing of constructively interfering plasmonic waves excited in the gap area between the nanoring and back-reflector mirror. For optimized MIM geometry excited by radially polarized CVB, substantial enhancement of the electromagnetic near-fields at the center of the ring within a single focal spot with the size of 0.37λ2 can be achieved, which is confirmed by Finite Difference Time Domain calculations, as well as by detection of 100-fold enhanced photoluminescent signal from adsorbed organic dye molecules. Simple large-scale and cost-efficient fabrication procedure offering also a freedom in the choice of materials to design MIM structures, along with remarkable optical and plasmonic characteristics of the produced structures make them promising for realization of various nanophotonic and biosensing platforms that utilize cylindrical vector beam as a pump source.
关键词： plasmonic nanostructures,cylindrical Vector Beam printing,Sensing Applications,nanofocusing,plasmonic nanolenses
更新于2025-09-12 10:27:22
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Fabrication of a precise ellipsoidal mirror for soft X-ray nanofocusing
摘要： In X-ray focusing, grazing incidence mirrors offer advantages of no chromatic aberration and high focusing ef?ciency. Although nanofocusing mirrors have been developed for the hard X-ray region, there is no mirror with nanofocusing performance in the soft X-ray region. Designing a system with the ability to focus to a beam size smaller than 100 nm at an X-ray energy of less than 1 keV requires a numerical aperture larger than 0.01. This leads to dif?culties in the fabrication of a soft X-ray focusing mirror with high accuracy. Ellipsoidal mirrors enable soft X-ray focusing with a high numerical aperture. In this study, we report a production process for ellipsoidal mirrors involving mandrel fabrication and replication processes. The fabricated ellipsoidal mirror was assessed under partial illumination conditions at the soft X-ray beamline (BL25SU) of SPring-8. A focal spot size of less than 250 nm was con?rmed at 300 eV. The focusing tests indicated that the proposed fabrication process is promising for X-ray mirrors that have the form of a solid of revolution, including Wolter mirrors.
关键词： soft X-ray,fabrication process,ellipsoidal mirror,nanofocusing,X-ray focusing
更新于2025-09-04 15:30:14