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1. Slowing down x-ray photons in a vibrating recoilless resonant absorber

   https://doi.org/10.1038/s41598-022-24114-8  

   Khairulin, I. R.; Radeonychev, Y. V.; Kocharovskaya, Olga (December 2022, Scientific Reports)

   Abstract Recently, an observation of acoustically induced transparency (AIT) of a stainless-steel foil for resonant 14.4-keV photons from a radioactive 57 Co Mössbauer source due to collective uniform oscillations of atomic nuclei was reported [Phys Rev Lett 124,163602, 2020]. In this paper, we propose to use the steep resonant dispersion of the absorber within the AIT spectral window to dramatically reduce a propagation velocity of γ-ray and x-ray photons. In particular, we show that a significant fraction (more than 40%) of a 97-ns γ-ray single-photon wave packet from a 57 Co radioactive source can be slowed down up to 3 m/s and delayed by 144 ns in a 57 Fe-enriched stainless-steel foil at room temperature. We also show that a similarly significant slowing down up to 24 m/s and a delay by 42 ns can be achieved for more than 70% of the 100-ns 14.4-keV x-ray single-photon pulse from a synchrotron Mössbauer source available at European Synchrotron Radiation Facility (ESRF) and Spring-8 facility. The propagation velocity can be widely controlled by changing the absorber vibration frequency. Achieving the propagation velocity on the order of 1–50 m/s would set a record in the hard x-ray range, comparable to what was obtained in the optical range. 

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2. Diffraction data from aerosolized Coliphage PR772 virus particles imaged with the Linac Coherent Light Source

   https://doi.org/10.1038/s41597-020-00745-2  

   Li, Haoyuan; Nazari, Reza; Abbey, Brian; Alvarez, Roberto; Aquila, Andrew; Ayyer, Kartik; Barty, Anton; Berntsen, Peter; Bielecki, Johan; Pietrini, Alberto; et al (December 2020, Scientific Data)

   Abstract Single Particle Imaging (SPI) with intense coherent X-ray pulses from X-ray free-electron lasers (XFELs) has the potential to produce molecular structures without the need for crystallization or freezing. Here we present a dataset of 285,944 diffraction patterns from aerosolized Coliphage PR772 virus particles injected into the femtosecond X-ray pulses of the Linac Coherent Light Source (LCLS). Additional exposures with background information are also deposited. The diffraction data were collected at the Atomic, Molecular and Optical Science Instrument (AMO) of the LCLS in 4 experimental beam times during a period of four years. The photon energy was either 1.2 or 1.7 keV and the pulse energy was between 2 and 4 mJ in a focal spot of about 1.3μm x 1.7μm full width at half maximum (FWHM). The X-ray laser pulses captured the particles in random orientations. The data offer insight into aerosolised virus particles in the gas phase, contain information relevant to improving experimental parameters, and provide a basis for developing algorithms for image analysis and reconstruction. 

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3. Transient lattice deformations of crystals studied by means of ultrafast time-resolved x-ray and electron diffraction

   https://doi.org/10.1063/1.5029970  

   Li, Runze; Sundqvist, Kyle; Chen, Jie; Elsayed-Ali, H_E; Zhang, Jie; Rentzepis, Peter_M (June 2018, Structural Dynamics)

   Ultrafast lattice deformation of tens to hundreds of nanometer thick metallic crystals, after femtosecond laser excitation, was measured directly using 8.04 keV subpicosecond x-ray and 59 keV femtosecond electron pulses. Coherent phonons were generated in both single crystal and polycrystalline films. Lattice compression was observed within the first few picoseconds after laser irradiation in single crystal aluminum, which was attributed to the generation of a blast force and the propagation of elastic waves. The different time scales of lattice heating for tens and hundreds nanometer thick films are clearly distinguished by electron and x-ray pulse diffraction. The electron and lattice heating due to ultrafast deposition of photon energy was simulated using the two-temperature model and the results agreed with experimental observations. This study demonstrates that the combination of two complementary ultrafast time-resolved methods, ultrafast x-ray, and electron diffraction will provide a panoramic picture of the transient structural changes in crystals. 

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4. Acoustically induced transparency for synchrotron hard x-ray photons

   https://doi.org/10.1038/s41598-021-86555-x  

   Khairulin, I. R.; Radeonychev, Y. V.; Antonov, V. A.; Kocharovskaya, Olga (April 2021, Scientific Reports)

   Abstract The induced transparency of opaque medium for resonant electromagnetic radiation is a powerful tool for manipulating the field-matter interaction. Various techniques to make different physical systems transparent for radiation from microwaves to x-rays were implemented. Most of them are based on the modification of the quantum-optical properties of the medium under the action of an external coherent electromagnetic field. Recently, an observation of acoustically induced transparency (AIT) of the⁵⁷Fe absorber for resonant 14.4-keV photons from the radioactive⁵⁷Co source was reported. About 150-fold suppression of the resonant absorption of photons due to collective acoustic oscillations of the nuclei was demonstrated. In this paper, we extend the AIT phenomenon to a novel phase-locked regime, when the transmitted photons are synchronized with the absorber vibration. We show that the advantages of synchrotron Mössbauer sources such as the deterministic periodic emission of radiation and controlled spectral-temporal characteristics of the emitted photons along with high-intensity photon flux in a tightly focused beam, make it possible to efficiently implement this regime, paving the way for the development of the acoustically controlled interface between hard x-ray photons and nuclear ensembles. 

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5. Dynamic optical spectroscopy and pyrometry of static targets under optical and x-ray laser heating at the European XFEL

   https://doi.org/10.1063/5.0142196  

   Ball, O_B; Prescher, C.; Appel, K.; Baehtz, C.; Baron, M_A; Briggs, R.; Cerantola, V.; Chantel, J.; Chariton, S.; Coleman, A_L; et al (August 2023, Journal of Applied Physics)

   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. 

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