Multiwavelength Surface‐Enhanced Raman Spectroscopy Using Rainbow Trapping in Width‐Graded Plasmonic Gratings

Abstract

as plasmonic hot-spots. [2] The resulting spectroscopic technique, known as surface-enhanced Raman spectroscopy (SERS), [3] surpasses the inherently low sensitivity of Raman by counterbalancing its low scattering efficiency [4] through spatial localization of the sample molecules proximal to the hot-spots on SERS substrates. So far colloidal nanoparticles of various shapes and sizes have been extensively used in SERS; [5][6][7][8][9] however, the lack of control over their relative orientation and separation limits efficient plasmonic coupling therebetween. [10] While this issue is addressed in SERS substrates made of immobilized nanoparticles, [11][12][13][14] interparticle gaps in these substrates are typically optimized to generate maximum field confinement for single wavelengths. Broadband SERS substrates can be made by immobilizing a mixture of nanoparticles resonant over a range of laser wavelengths on surface plasmon polariton (SPP)-supporting thin films. [15,16] However, the magnitude of SERS signal enhancement and the broadband nature of such substrates remain highly dependent on the nanoparticle-film separation as well as the interparticle distances which are difficult to control in practice. More robust broadband SERS substrates have been recently fabricated by sputtering randomly sized silver nanoparticles on glass-silver-glass multilayered substrates, [17] yielding plasmonic resonances over the 400-1100 nm

Rainbow Trapping with Long Oscillation Lifetimes in Gradient Magnetoinductive Metasurfaces

“…Most previous works can be classified as dispersion engineering, where waveguides with tailored dispersion characteristics are the key to make waves of different wavelengths halt at desirable positions. Gratings were widely utilized to slow down surface plasmons to a * 230159363@seu.edu.cn † shijun@caltech.edu ‡ 101010074@seu.edu.cn § dsievenpiper@eng.ucsd.edu standstill to obtain rainbow trapping [18][19][20][21]. Similar phenomena were also reported in photonic crystals [22][23][24] as well as metal-insulator-metal tapered plasmonic waveguides [16].…”

Multiresonant plasmonics with spatial mode overlap: overview and outlook

“…In this section, we briefly discuss the strategy to build multiresonant plasmonic systems through the optical coupling between delocalized plasmonic modes based on rainbow trapping effect in graded grating structures [157][158][159][160][161]. Figure 9A and B represent a width-graded rainbow trapping 1D plasmonic nanograting structure [161]. We can consider each groove unit as a lossy Fabry-Perot resonator supporting SPP standing waves bouncing back and forth between the two silver side walls.…”

“…A multiresonant plasmonic system based on the optical coupling between delocalized plasmonic modes[161]. (A) The SEM image of a width-graded rainbow trapping 1D plasmonic nanograting consisting of 29 in-plane MIM rectangular grooves separated from each other by 100 nm thick mesas.…”

Tunable rainbow light trapping in ultrathin resonator arrays

“…We then utilise these calculations to design resonator arrays capable of rainbow trapping by varying the width and length of the contained nanogrooves and, for the first time, by varying both parameters together. These arrays are fabricated using a multilayer thin-film deposition and focused ion beam (FIB) milling technique whereby groove-widths as small as 5 nm are attainedan order of magnitude smaller than that reported in previous rainbow trapping studies 31,33 , which provide extremely large localised field enhancements up to 10 3 . Finally, the rainbow trapping capabilities of these devices are demonstrated via far-field hyperspectral microscopy.…”

“…Typically, these designs consist of arrays of resonators, with resonant wavelengths determined by the size, shape and composition of the individual units 3 . Combining nanostructures with different resonant wavelengths, for example multiresonant nanoparticles 29 and nanocavities [30][31][32][33] , into a single device provides tunable, position-dependent rainbow field enhancement. However, given the lack of analytical solutions for these resonators, it is not feasible to accurately predict the resonant properties of the nanostructures at the design stage without running a large number of iterative detailed simulations.…”