Nonlocal Flat Optics for Z-Pinch Plasma Edge Detection

Many high-energy-density (HED) physics measurements on laboratory plasmas involve identifying edges in object images, including measuring the radii of collapsing Z-pinch plasmas and following shadowgraphy or interferometry lines. Typically, edge tracing is performed though digital signal processing or by hand. However, recent developments in “nonlocal” (i.e., wavevector-sensitive) optics enable physical analog light processing, including edge enhancement, via designing a structure’s wavevector-dependent transfer function to act as a high-pass spatial-frequency filter for incident light.

This work presents multilayer thin-film optics, which strongly transmit plasma edges and remove background features. Gradient-based optimization of each layer’s thickness and permittivity targets a second or third spatial derivative, replicating and applying the work of Xue, W., & Miller, O. D., as well as Silva, A., et al. to plasma diagnostics [1, 2]. This speed-of-light processing is simulated on Z-pinch plasmas, using interferometry images from the Laboratory of Plasma Studies’ (LPS) Cornell Beam Research Accelerator (COBRA) pulsed-power machine and 532 nm laser. By passively highlighting fringes at any time instant, the nonlocal optic can make post-processing computations faster or more effective.

[1] Xue, W., & Miller, O. D. (2021). Journal of Optics, 23(12), 125004.

[2] Silva, A., et al. (2014). Science, 343(6167), 160-163.