HERFD: High Energy Resolution Fluorescence Detected

The high-energy-resolution fluorescence detection technique, HERFD, makes possible to overcome some of the main limitations of conventional XAS. This technique consists of measuring the X-ray absorption spectrum via monitoring the intensity of a fluorescence line corresponding to a specific excited state decay process using a narrow energy resolution. This is generally achieved through the use of a crystal analyser to select a narrow energy band from the sample’s emission line. 

HERFD-XANES is applying the high-energy-resolution fluorescence detection technique to the near edge structures of the absorption spectra. As this is XANES it tends to be in the hard X-ray range.