Inverse design of nanoparticles for enhanced Raman scattering

Abstract

We show that topology optimization (TO) of metallic resonators can lead to ∼ 10 2 × improvement in surfaceenhanced Raman scattering (SERS) efficiency compared to traditional resonant structures such as bowtie antennas. TO inverse design leads to surprising structures very different from conventional designs, which simultaneously optimize focusing of the incident wave and emission from the Raman dipole. We consider isolated metallic particles as well as more complicated configurations such as periodic surfaces or resonators coupled to dielectric waveguides, and the benefits of TO are even greater in the latter case. Our results are motivated by recent rigorous upper bounds to Raman scattering enhancement, and shed light on the extent to which these bounds are achievable. * Corresponding

Approaching the upper limits of the local density of states via optimized metallic cavities

“…Since the spontaneous symmetry-breaking in the previous section suggests that optimization favors maximizing LDOS in a single direction, we now consider optimizing the polarized LDOS. That is, we maximize the power expended by a dipole current with a single orientation (similar to previous work on cavity optimization in dielectric media [14,32,33]). As above, we performed few-parameter optimization of ellipsoids, cylinders, and rectangular boxes.…”

“…Many previous authors have computationally optimized the LDOS of cavities (or equivalent quantities such as the Purcell factor Q/V), including many-parameter shape or "topology" optimization [27][28][29][30][31][32], but in most cases these works did not compare to the recent upper bounds. In many cases, these works studied lossless dielectric materials where the bound diverges (though a finite LDOS is obtained for a finite volume [14,33] and/or a finite bandwidth [13,14]). Designs specifically for LDOS of metallic resonators that compared to the bounds initially yielded results far below the bounds except for the special case of a planar surface at the surface-plasmon frequency of the material [1,34], but recent topology optimization in two dimensions came within a factor of 10 of the 2D bound [33].…”

“…In many cases, these works studied lossless dielectric materials where the bound diverges (though a finite LDOS is obtained for a finite volume [14,33] and/or a finite bandwidth [13,14]). Designs specifically for LDOS of metallic resonators that compared to the bounds initially yielded results far below the bounds except for the special case of a planar surface at the surface-plasmon frequency of the material [1,34], but recent topology optimization in two dimensions came within a factor of 10 of the 2D bound [33]. Semi-analytical calculations have also been published for resonant modes in spherical metallic voids [35], but did not calculate LDOS.…”

Inverse design in photonics by topology optimization: tutorial

“…Indeed, the main challenge when applying TopOpt is often to limit the design freedom offered by the method, in a way that conforms with fabrication constraints. Within photonics and plasmonics, TopOpt has received increasing attention over the last two decades [8,10] with recent examples of applicationss including the design of dielectric multiplexers [11], dielectric metalenses [12][13][14], extreme dielectric confinement structures [15,16], plasmonic nano-antennas [17], and plasmonic nanoparticles for solar cell 0740-3224/21/020496-14 Journal © 2021 Optical Society of America applications [18,19] and for enhanced thermal emission [20] and Raman scattering [21], to name but a few.…”

The Effects of ZnO particles on the color homogeneity of phosphor-converted high-power white LED light sources

“…With outstanding performance and remarkable features that improve the lighting efficiency, durability, power-saving as well as the low waste-emission rate, the Light-emitting diodes (LEDs) has grown passed many traditional lighting methods and become one of the most reliable light source for modern solid-state lighting [1][2][3][4]. However, to keep the development going, there must be improvements in the way that the white light in these LEDs is produced, which is integrating the blue light from a chip and yellow light from yellowish phosphor, known as YAG:Ce [5,6].…”