High-spectral-resolution absorption measurements with free-electron lasers using ghost spectroscopy

We demonstrate a simple and robust high-resolution ghost spectroscopy approach for x-ray and extreme ultraviolet transient absorption spectroscopy at free-electron laser sources. To retrieve the sample response, our approach requires only an online spectrometer before the sample and a downstream bucket detector. We validate the method by measuring the absorption spectrum of silicon, silicon carbide, and silicon nitride membranes in the vicinity of the silicon L2,3 edge and by comparing the results with standard techniques for absorption measurements. Moreover, we show that ghost spectroscopy allows the high-resolution reconstruction of the sample spectral response to optical pumps using a coarse energy scan with self-amplified spontaneous emission radiation.