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

Abstract

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 L 2,3 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.

Free electron laser stochastic spectroscopy revealing silicon bond softening dynamics

“…The spectrum clearly displays two EUV transmission drops assigned to the spin-orbit split resonances of the 2p levels at 99.76 eV (L 3 edge) and 100.45 eV (L 2 edge), corresponding, respectively, to emission features C and E. The present data are compared with (i) a spectrum from a nominally identical sample obtained by a synchrotron measurement (at the BEAR beamline of the Elettra synchrotron [61], yellow line) with comparable energy resolution and acquisition time; (ii) a measurement performed at FERMI by using narrow-band (seeded-mode) FEL emission and scanning the photon energy (gray line). It is worth noticing the lower-energy resolution of about 75 meV due to the reduced number of experimental points collected in the same acquisition time (2 h); and (iii) a measurement performed at FERMI (in SASE-like mode) obtained by exploiting the ghost spectroscopy method (green line) [18]: The energy and temporal resolution, as well as the acquisition time, are comparable.…”

“…In this respect, it is highly desirable to develop multiplexing approaches capable of simultaneously exploiting a large spectral bandwidth without the need for spectral filtering and photon-energy scanning. An elegant and effective solution to multiplex-based spectroscopy is represented by correlation spectroscopy methods based on the determination of the statistical fluctuations introduced by the interaction of the light pulses with the sample; such approaches have been realized both in the optical region [14,15] as well as in the x-ray range [16][17][18][19].…”