Time dependence of Bragg forward scattering and self-seeding of hard x-ray free-electron lasers

Free-electron lasers (FELs) can now generate temporally short, high power x-ray pulses of unprecedented brightness, even though their longitudinal coherence is relatively poor. The longitudinal coherence can be potentially improved by employing narrow bandwidth x-ray crystal optics, in which case one must also understand how the crystal affects the field profile in time and space. We frame the dynamical theory of x-ray diffraction as a set of coupled waves in order to derive analytic expressions for the spatiotemporal response of Bragg scattering from temporally short incident pulses. We compute the profiles of both the reflected and forward scattered x-ray pulses, showing that the time delay of the wave $\tau$ is linked to its transverse spatial shift $\Delta x$ through the simple relationship $\Delta x = c\tau \cot\theta$, where $\theta$ is the grazing angle of incidence to the diffracting planes. Finally, we apply our findings to obtain an analytic description of Bragg forward scattering relevant to monochromatically seed hard x-ray FELs.Comment: 11 pages, 6 figure

Single-Photon Entanglement in the keV Regime via Coherent Control of Nuclear Forward Scattering

Generation of single-photon entanglement is discussed in nuclear forward scattering. Using successive switchings of the direction of the nuclear hyperfine magnetic field, the coherent scattering of photons on nuclei is controlled such that two signal pulses are generated out of one initial pump pulse. The two time-resolved correlated signal pulses have different polarizations and energy in the keV regime. Spatial separation of the entangled field modes and extraction of the signal from the background can be achieved with the help of state-of-the-art x-ray polarizers and piezoelectric fast steering mirrors.Comment: minor changes, updated to the final version; 4 pages, 2 figure

Hybrid forms of beat phenomena in nuclear forward scattering of synchrotron radiation

In nuclear forward scattering (NFS) of synchrotron radiation, inter-resonance interferenceleads to a quantum beat (QB), and intra-resonance interference to a dynamical beat (DB).In general both interference processes determine the time evolution of NFS. Only in thecase of far distant resonances the resulting interference pattern can be interpreted as awell distinguishable combination of QB and DB. Multiple scattering by near neighbouringresonances, by contrast, leads to a hybridisation of QB and DB. In particular, asymmetricalcontinuous distributions of resonances make QB and DB blend into a fast hybrid beat withthickness dependent period and distribution sensitive modulatio

Понятие и признаки произвола

Mössbauer time spectra were studied under the condition of abrupt inversion of the hyperfine magnetic fields. The 14.4-keV nuclear resonance of 57Fe in an 57FeBO3 crystal was excited by synchrotron radiation pulses in Bragg-diffraction conditions. Fast inversion of the crystal magnetization and the hyperfine magnetic fields causes the time reversal of the quantum-beat pattern in the Mössbauer time spectra

Pulse propagation of synchrotron radiation through a nuclear two-resonance system

Pulse propagation through a two-resonance medium was investigated in nuclear forward scattering (NFS) of synchrotron radiation (SR). The SR pulse was coherently transmitted through a target system exhibiting two equivalent resonances, the energy separation of which was varied via the Doppler effect. This allowed a continuous change from a single-resonance medium to a two-resonance system with adjustable splitting. For increasing splitting, the observed time evolutions of NFS changed from a dynamical beat (DB) via hybrid forms of beating into a DB-modulated quantum beat. The experimental results were consistently fitted using a dynamical theory for NFS of SR