Multilayer coating design methods for a high-energy x-ray imaging optic with complex design requirements

Imaging of x-rays with energies >15 keV is a necessity for several applications in high-energy density physics experiments. Multilayer-coated, Wolter-type glancing-incidence optics offer higher collection efficiency than pinhole cameras or Kirkpatrick-Baez style mirrors, and can achieve spatial resolution of 10-100um over 1-8 mm fields of view with throughput similar to 1-10%. Designing the multilayer coating is a complex optimization problem, involving multiple tradeoffs. A narrow energy bandwidth (similar to 1keV) is desirable to exclude background, but a broad angular acceptance is desirable for the optic to image a large field (similar to 1-8 mm). A Wolter optic's net reflectivity is two-bounce R-2 = R-1*R-2 for a wide range of pairs of incidence angles theta(1), theta(2). In addition, the multilayer coating can be modified in several ways, such as varying the period thickness through the stack, and along the length of the optic. Parallelized searches using ordinary gradient-descent and Markov-Chain Monte Carlo (MCMC) have been applied to design an optic to image Z-pinch plasmas on the Z Machine at Sandia National Laboratories. Methods are tested to design an appropriate cost function for this search, and to reduce computational cost to search the parameter space efficiently.