Topology-optimized distributed 3d anisotropic Raman emission

TL;DR

This paper introduces a topology optimization method for 3D SERS substrates that maximizes Raman signals from randomly oriented anisotropic molecules, addressing modeling challenges and demonstrating manufacturable, broadband-enhanced designs.

Contribution

A novel trace formulation for rotational averaging of anisotropic Raman tensors and a topology optimization framework for manufacturable 3D SERS substrates.

Findings

Metallic designs provide broadband enhancement and robustness.

Dielectric designs offer narrower, quality-factor-limited gains.

Lengthscale constraints prevent unphysical field divergences.

Abstract

Topology optimization (TO) of 3D surface-enhanced Raman scattering (SERS) substrates faces challenges in managing field singularities and modeling orientation-averaged anisotropic molecules. We present 3D TO for manufacturable SERS substrates that maximize spatially averaged signals from randomly oriented, anisotropic molecules in both elastic and inelastic scattering. A new trace formulation provides a closed-form rotational average of anisotropic Raman tensors, which are not equivalent to isotropic molecules because of tensor nonlinearity. Optimized silver and Si3N4 devices show that lengthscale constraints are sufficient to suppress designs that rely on unphysical mathematical field divergences at sharp corners. Metallic designs deliver broadband enhancement and remain robust to typical Raman shifts, whereas dielectric designs yield narrower, quality-factor-limited gains that are inferior to metallic designs for quality factors below about 500. Our approach readily incorporates additional physics, such as a nonlinear damage model. Together, these results provide a practical route to improved manufacturable SERS substrates and extend naturally to other distributed-emitter design problems.