Optical microcavity structures for time-resolved meso-scale sensing of pressure during shock-compression of heterogeneous materials

Abstract

Optical microcavity structures (OMCs) exhibit unique spectral responses that can be correlated to externally applied loads, with the potential to be used as time-resolved pressure sensors during dynamic or shock-compression loading of heterogeneous materials. Particulates, engineered composites, and energetic materials are examples of heterogeneous materials that display complex meso-scale behaviors, affecting their shock-compression response. A fundamental challenge is the lack of experimental diagnostics available for spatiotemporal measurements of the shock-compression conditions generated in heterogeneous materials. This work presents the theoretical and experimental development, and evaluation, of OMCs, as time-resolved pressure sensors with meso-scale spatial sensitivity. Laser-driven uniaxial-strain shock-compression of OMCs demonstrated shifts of characteristic spectral peaks to shorter wavelengths (blueshifts) that unambiguously correlate with simultaneous velocimetry measurements for deducing the shock pressure. An optomechanical model was developed to predict the spectral response of OMCs as a function of pressure. When informed with quality empirical data, the model showed quantitative matching with the experimentally observed blueshift. Subsequent experiments and simulations of spatially heterogeneous shock loading demonstrated the ability of OMCs to not only resolve multiple pressures but also to capture the subtle features present in shock-compressed heterogeneous materials, all while maintaining nano-second level temporal resolution. The overall results provide the theoretical and empirical foundation and demonstrate the unique potential of OMCs as sensors for capturing the complex meso-scale pressure histories needed to enable new insights into the complex shock-compression response of heterogeneous materials.