Advanced Optical Diagnostics

Understanding complex materials with highly heterogeneous structures and properties is a significant scientific and engineering challenge. The multi-scale behavior of these materials is very difficult to model and predict, resulting in significant gaps in understanding for many important classes of materials including granular materials such as sand and soil, energetic materials, and engineered composites.

The behavior of these materials under high-strain-rate loading is even more complex, due to the extreme conditions of pressure, temperature, and strain under such loading. For example, Figure 1 below demonstrates a high-pressure shock wave propagating through collection of spherical particles, and the highly stochastic path of the stress and strain due to the random nature of the particle orientations is apparent. In order to better understand how these complex materials behave, advanced experimental diagnostics that can measure how the material responds both in time and space are needed.

Figure 1. Simulated shock compression of a random packing of silica (sand) particles.

Multilayer optical structures, a class of 1-dimensional photonic crystals, have the potential to provide this essential information. By recording the changes of the multilayer’s unique optical signature under dynamic loading, an optical pressure sensor with high temporal and spatial resolution can be demonstrated. These multilayers sensors have the potential to provide significant insight into the mechanisms driving the behavior of complex heterogeneous materials.

Figure 2. Reflectance spectra of a Distributed Bragg Reflector (DBR) multilayer structure under laser-driven shock compression. The shift to lower wavelengths as a function a time represent the time-resolved pressure state of the material.