Measurement-Aware Computational Modeling for Optical Spectrometry in Scattering-Dominated Systems.

Computational modeling is widely used to interpret optical spectrometric data; however, most prevailing approaches extrapolate isolated-particle optical cross sections to finite concentrations without explicitly accounting for photon transport, multiple scattering, and instrument geometry. In scattering-dominated systems, this simplification introduces systematic discrepancy between theoretical predictions and measured extinction and polarization signals, often misattributed to intrinsic material changes. Here, we develop a measurement-aware, physics-guided computational framework that integrates electrodynamic theory with Monte Carlo photon transport simulations and supervised least-squares parameter estimation under realistic experimental conditions. Rather than relying on direct extrapolation of single-particle responses, the framework forward-simulates photon trajectories within a finite sample volume, explicitly incorporating multiple scattering and detector collection constraints. A limited set of effective parameters, including collection geometry and refractive index, is inferred through cross-validated regression to enable quantitative comparison with experimental measurements. Using spherical polystyrene suspensions spanning three size regimes (100, 380, and 1060 nm) and broad concentration ranges, the model reproduces experimentally measured UV-Vis extinction spectra exhibiting pronounced nonlinear concentration dependence. The framework captures regimes in which Beer-Lambert extrapolation predicts optical densities of 5-9, whereas measured signals remain below 4 within the instrument's linear dynamic range due to geometry-dependent photon redistribution. Spatial- and polarization-resolved simulations further show that multiple scattering reshapes both intensity and polarization in an orientation-, concentration-, and aperture-dependent manner, fundamentally altering the mapping between concentration and detected signal. By explicitly incorporating transport effects as part of the measurement process, this approach enables consistent extraction of effective refractive indices across independent particle sizes and data sets. The results establish a quantitative framework for reconciling theory with experiments in scattering-dominated optical systems and provide a scalable pathway for modeling more complex absorbing and emissive materials.