Evaluation and optimization of multilayer designs for astronomical x-ray telescopes using a field-of-view- and energy-dependent figure of merit

The three most important quantities used to assess the performance of astronomical x-ray telescope optics are the on- axis collecting area, the field of view, and the half-power diameter. The first two quantities depend on the mirror packing arrangement and the multilayer coating design. In order to optimize the coating design, we have developed a figure-of-merit (FOM) that accounts for the coating response over a specified range of energies and off-axis angles. We present an example where we have used this FOM to optimize a specific coating design for the High Energy Focusing Telescope (HEFT) and to understand tradeoffs between performance and coating thickness.