Abstract
We describe a laser-driven x-ray plasma source designed for ultrafast x-ray absorption spectroscopy. The source is comprised of a 1 kHz, 20 W, femtosecond pulsed infrared laser and a water target. We present the x-ray spectra as a function of laser energy and pulse duration. Additionally, we investigate the plasma temperature and photon flux as we vary the laser energy. We obtain a 75 μm FWHM x-ray spot size, containing ∼106 photons/s, by focusing the produced x-rays with a polycapillary optic. Since the acquisition of x-ray absorption spectra requires the averaging of measurements from >107 laser pulses, we also present data on the source stability, including single pulse measurements of the x-ray yield and the x-ray spectral shape. In single pulse measurements, the x-ray flux has a measured standard deviation of 8%, where the laser pointing is the main cause of variability. Further, we show that the variability in x-ray spectral shape from single pulses is low, thus justifying the combining of x-rays obtained from different laser pulses into a single spectrum. Finally, we show a static x-ray absorption spectrum of a ferrioxalate solution as detected by a microcalorimeter array. Altogether, our results demonstrate that this water-jet based plasma source is a suitable candidate for laboratory-based time-resolved x-ray absorption spectroscopy experiments.
Highlights
The study of the structural dynamics in matter has been enabled by experimental tools such as time-resolved x-ray diffraction and absorption.[1,2] The short wavelength of x-ray light enables materials to be probed at the atomic level and the large penetration depth of hard x-ray light is well suited for the study of crystals, molecules, and protein structures
Since the acquisition of x-ray absorption spectra requires the averaging of measurements from many laser pulses, we present data on the source stability, including single pulse measurements of the x-ray yield and the x-ray spectral shape
We have presented an x-ray plasma source for ultrafast x-ray absorption spectroscopy
Summary
The study of the structural dynamics in matter has been enabled by experimental tools such as time-resolved x-ray diffraction and absorption.[1,2] The short wavelength of x-ray light enables materials to be probed at the atomic level and the large penetration depth of hard x-ray light is well suited for the study of crystals, molecules, and protein structures. The development of laser-driven plasma sources has enabled ultrafast XAS measurements to be performed in laboratory settings.[8–10] Important characteristics of these table-top x-ray sources relevant for time-resolved XAS are: ultrashort pulse durations, a continuous spectrum from soft to hard x-ray energies, intrinsic all optical and, in principle, jitter-free synchronization with the exciting light source, sufficient photon fluxes, and long-term stability. Liquidtarget sources have clear benefits for stable, long-term operation: the target is replenished and debris can be removed from the surfaces of the target enclosure, in some cases by the same pumping action that evacuates the enclosure In this manuscript, we describe an x-ray plasma source with a water target designed for ultrafast XAS. Our results demonstrate that this water-jet based plasma source is a suitable candidate for laboratory-based time-resolved x-ray absorption spectroscopy experiments
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