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 Kα line (8.0keV).
@article{arxiv.1611.07856,
title = {When "Optimal Filtering" Isn't},
author = {J. W. Fowler and B. K. Alpert and W. B. Doriese and J. Hays-Wehle and Y. -I. Joe and K. M. Morgan and G. C. O'Neil and C. D. Reintsema and D. R. Schmidt and J. N. Ullom and D. S. Swetz},
journal= {arXiv preprint arXiv:1611.07856},
year = {2017}
}
Comments
Submitted to the Proceedings of the 2016 Applied Superconductivity Conference