When "Optimal Filtering" Isn't
  The so-called "optimal filter" analysis of a microcalorimeter's x-ray pulses is statistically optimal only if all pulses have the same shape, regardless of energy. The shapes of pulses from a nonlinear detector can and do depend on the pulse energy, however. A pulse-fitting procedure that we call "tangent filtering" accounts for the energy dependence of the shape and should therefore achieve superior energy resolution. We take a geometric view of the pulse-fitting problem and give expressions to predict how much the energy resolution stands to benefit from such a procedure. We also demonstrate the method with a case study of K-line fluorescence from several 3d transition metals. The method improves the resolution from 4.9 eV to 4.2 eV at the Cu K$\alpha$ line (8.0keV). 
J. W. Fowler, B. K. Alpert, W. B. Doriese, J. Hays-Wehle, Y.-I. Joe,   K. M. Morgan, G. C. O'Neil, C. D. Reintsema, D. R. Sc...
physics.data-an astro-ph.IM physics.ins-det