High energy resolution fluorescence detection (HERFD)
From Online Dictionary of Crystallography
High energy resolution fluorescence detection (HERFD) requires measurement of the fluorescence lines with an instrumental energy bandwidth on the order of or below the core hole lifetime broadening of the absorption edge (see XES). A HERFD-XAS experiment measures the intensity of the fluorescence line as a function of the incident energy (fluorescence-detected XAS, secondary process detection) and may yield spectral features with line broadenings that are smaller than the lifetime broadening of the core hole excited state of absorption. HERFD has to be understood within the framework of resonant X-ray emission spectroscopy (RXES). A HERFD-XAS spectrum may present a good approximation to the absorption cross section with reduced lifetime broadening. This is, however, not necessarily the case and has to be carefully verified.