Time-resolved Sensing of Shock Pressure Distributions Using OPTO-Mechanical Multi-layer Photonic Crystal Structures*

We are investigating the design and application of optomechanical sensors based on a \textit{Distributed Bragg Reflector (DBR)} composed of dielectric stacks of alternating high and low refractive index materials, and an \textit{Optical Micro Cavity (OMC)} composed of a dielectric cavity-layer placed between two metal mirrors. These 1-D photonic crystal structures generate size-tunable characteristic spectral changes observed as reflectance peak (for DBRs), or minima (for OMCs) as a function of pressure. Unlike commonly utilized piezoresistive/piezoelectric stress sensors, which provide volume-averaged responses, optomechanical sensors can provide mapping of spatially and temporally resolved pressures, and their distributions across a shocked surface. In this presentation, responses obtained by directly subjecting the DBR (\textasciitilde 5 \textmu m thick) and OMC (\textasciitilde 1 \textmu m thick) structures to homogeneous and heterogeneous pressures, using laser-driven shocks and time-resolved spectroscopy enabled by spectrograph-coupled streak camera, will be described, along with results of optomechanical simulations utilizing a custom multi-physics framework. The results reveal a highly time-resolved spectral response to shock loading manifesting as wavelength shifts as a function of pressure, which correlate well with simulations. The ability to capture pressure distributions with micro-scale spatial variations is also demonstrated for particulate materials.