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Dynamic optical spectroscopy and pyrometry of static targets under optical and x-ray laser heating at the European XFEL
Ist Teil von
Journal of applied physics, 2023-08, Vol.134 (5)
Ort / Verlag
Melville: American Institute of Physics
Erscheinungsjahr
2023
Quelle
American Institute of Physics (AIP) Journals
Beschreibungen/Notizen
Experiments accessing extreme conditions at x-ray free electron lasers (XFELs) involve
rapidly evolving conditions of temperature. Here, we report time-resolved, direct
measurements of temperature using spectral streaked optical pyrometry of x-ray and optical
laser-heated states at the High Energy Density instrument of the European XFEL. This
collection of typical experiments, coupled with numerical models, outlines the
reliability, precision, and meaning of time dependent temperature measurements using
optical emission at XFEL sources. Dynamic temperatures above 1500 K are measured
continuously from spectrally- and temporally-resolved thermal emission at 450–850 nm, with
time resolution down to 10–100 ns for 1–200
μs streak camera windows, using single
shot and integrated modes. Targets include zero-pressure foils free-standing in air and
in vacuo, and high-pressure samples compressed in diamond
anvil cell multi-layer targets. Radiation sources used are 20-fs hard x-ray laser pulses
at 17.8 keV, in single pulses or 2.26 MHz pulse trains of up to 30 pulses, and 250-ns
infrared laser single pulses. A range of further possibilities for optical measurements of
visible light in x-ray laser experiments using streak optical spectroscopy are also
explored, including for the study of x-ray induced optical fluorescence, which often
appears as background in thermal radiation measurements. We establish several scenarios
where combined emissions from multiple sources are observed and discuss their
interpretation. Challenges posed by using x-ray lasers as non-invasive probes of the
sample state are addressed.