Ultrasoft (C,N,O) x-ray fluorescence detection: Proportional counters, focusing multilayer mirrors, and scattered light systematics (invited)

Ultrasoft x-ray detection is discussed as applied to the fluorescence yield near edge spectroscopy (FYNES) technique. We describe a progression of improved ultra-high vacuum compatible soft x-ray proportional counters for FYNES measurements. The importance of energy dispersive detection is discussed and examples shown. Scattered light background problems are quantified and compared for several real samples. Finally, focusing multilayer mirror collection is introduced for reducing scattered light background and improved elemental differentiation in the fluorescence signal.