Coherent X-ray radiation generated by a beam of relativistic electrons in a single crystal under conditions of multiple scattering

The dynamic theory of the coherent X-ray radiation of a divergent beam of relativistic electrons generated in a single-crystal wafer under conditions of the multiple scattering of incident particles is developed. Radiation cross sections are averaged over the divergent beam of rectilinear trajectories of electrons. Expressions describing the spectral-angular characteristics of parametric X-ray radiation and diffracted transition radiation under conditions of multiple scattering are obtained. Conditions under which the contribution of diffracted brehmsstrahlung can be disregarded are shown, and the spectral-angular characteristics of parametric X-ray radiation and diffracted transition radiation are calculated numerically for such conditions.     

The X-ray radiation of ultrarelativistic electrons in a crystal

The properties of the coherent X-ray radiation of the ultrarelativistic electrons in a crystal are considered. The total number of X-ray and resonant γ-ray quantum emitted in a crystal under diffraction conditions are calculated.     

Coherent X-ray diffraction radiation produced by microbunched beams passing close to the edge of a slab

With use of formulas for single-particle X-ray transition and diffraction radiation (XTR and XDR), we obtain expressions for spectral-angular distributions and total numbers of emitted quanta in coherent X-ray transition radiation (CXTR2) and coherent X-ray diffraction radiation (CXDR) arising when a microbunched beam of electrons, respectively, intersects the interfaces of a slab or flies at small distance from the edge of the slab. Comparison of obtained results with those known for CXTR from a single interface is performed. It is shown on the basis of numerical calculations that experimental study of CXDR is at present possible on the Linac Coherent Light Source (LCLS, SLAC).     

第三代同步辐射光源X射线相干性测量研究

随着高性能第三代同步辐射光源的建成开放,基于X射线相干特性的实验方法得到了快速发展和广泛应用.作为一个典型的例子,X射线相位衬度成像已经成为常规的X射线实验方法并向用户开放.相干散射、相干衍射成像、光子关联谱等X射线实验方法正日益受到重视,在高空间分辨、时间分辨等研究领域已显示出其独特的优越性.因此,研究和测量第三代同步辐射的空间相干特性对进一步发展这些新的实验方法具有重要意义.基于Talbot自成像原理成功测量了上海光源X射线成像线站发射的X射线的空间相干长度,并进而测得了相应光源的空间尺度.光子能量为33.2 keV时,测得的X射线光束垂直方向空间相干长度为8.84μm,对应的光源尺寸为23μm,测量结果与理论分析相符.     

Coherent X-ray radiation generated by a relativistic electron in an artificial periodic structure

A theory of coherent X-ray radiation from a relativistic electron crossing an artificial periodic layered structure in the Laue scattering geometry is constructed. The expressions describing the spectral-angular radiation parameters are obtained. It is shown that the radiation yield in such a medium may substantially exceed the radiation yield in a crystal under analogous conditions.     

X-ray scattering in the presence of a strong laser field

Remarkable modifications of electron scattering in the presence of a strong, low frequency radiation field have been found by Kroll and Watson several years ago. It is shown that these modifications have their exact counterparts in the corresponding X-ray scattering by free and bound electrons. In view of the rapid development towards coherent X-ray sources, such induced radiation processes may become accessible to experimental verification in the near future.     

Diffracted transition radiation of relativistic electrons in an artificial periodic structure

A theory concerning the coherent X-ray radiation of relativistic electrons crossing an artificial periodic medium in Laue scattering geometry has been constructed. Expressions describing the spectralangular characteristics of radiation in the Bragg scattering direction have been obtained and studied. Radiation is considered in analogy with that in the crystal medium as a result of the coherent summation of the contributions of two radiation mechanisms, in particular, parametric X-ray radiation (PXR) and diffracted transition radiation (DTR). It is shown that the DTR yield from a layered target can exceed the particle radiation yield in a single-crystal radiator by one order or more under similar conditions.     

Interference effects in X-ray radiation from relativistic electrons moving at a small angle to an atomic plane

X-ray radiation of relativistic electrons interacting with a set of parallel atomic planes is considered. The anomalous behavior of the radiation due to the interplay of parametric and coherent bremsstrahlung emission mechanisms, which simultaneously occur under specific conditions, is studied.     

Coherent X-ray radiation from a relativistic electron in a combined medium

A theory of coherent X-ray radiation from a relativistic electron crossing a combined medium that consists of amorphous and crystal plates is constructed within the dynamic diffraction theory. The field reflection asymmetry relative to the target surface determined by the angle between the atomic planes and the target surface is taken into account in the theory. The expressions describing the spectral-angular densities of parametric X-ray and diffracted transition radiations in this medium are derived and investigated.     

Polarization of photons emitted in the process of resonant coherent excitation of relativistic ions under planar channeling conditions

Owing to the recent observation of the strong anisotropy of characteristic X-ray radiation accompanying the resonant coherent excitation of relativistic Fe²⁴⁺ ions under planar channeling conditions in a silicon crystal, the resonant coherent excitation method can be considered as a candidate for a source of polarized X-ray radiation. The Stokes parameters of the radiation have been calculated using the density matrix approach. The behavior of the polarization characteristics of the radiation in various directions has been explained by considering the properties of the resonance part of the crystal field, which excites an ion and has the form of an elliptically polarized electric field.     

Interference effects in the coherent X-ray radiation of relativistic electrons in two- and three-layer targets

A dynamic theory of the coherent X-ray radiation of relativistic electrons in “amorphous medium–single-crystal” and “amorphous medium–free-space–single-crystal” targets is developed. Expressions for the spectral-angular distributions of diffracted transition radiation (DTR), parametric X-ray radiation, and a term describing their interference are obtained. The spectral-angular density of the DTR is represented as a sum of terms describing the diffracted transition radiation from various boundaries and a term describing the interference of these components. Interference effects in the spectral-angular and angular densities of radiation are studied.     

上海软X射线自由电子激光外种子运行模式的模拟研究

上海软X射线自由电子激光用户装置（SXFEL）是我国首台可以运行在水窗波段的自由电子激光装置,未来可以为5个实验线站供光,其主要运行模式为自放大自发辐射模式以及外种子模式。本文就SXFEL的外种子模式进行了从头到尾的模拟研究,主要包括EEHG-HGHG混合级联与单级EEHG两种方案。模拟结果表明,虽然EEHG-HGHG混合级联模式较为复杂,但能够产生更高功率的高次谐波辐射。除此之外,我们还研究了各种三维效应对EEHG的影响。模拟和分析结果表明,通过上述两种方案,采用紫外波段的种子激光,用户可以得到全相干、窄带宽、短脉冲的水窗波段自由电子激光。     

X-ray transition radiation of electrons with energy of 300 to 900 MeV in periodic multifoil radiators

Results of experiments conducted at the Tomsk synchrotron to study resonant X-ray transition radiation generated by relativistic electrons in periodic multifoil radiators are reviewed. Both the internal synchrotron beam and the external secondary electron beam from the pair magnetic γ-spectrometer with energies ranging from 300 to 900 MeV were used in the experiments. The radiators consisted of many thin amorphous foils of various materials. The generation of X-ray radiation in a compound radiator consisting of a multifoil radiator and a crystal is also studied. In this case, the resonant X-ray transition radiation generated in the multifoil radiator is diffracted in the crystal and emitted at Bragg angles, together with the parametric X-ray radiation generated in the crystal. Spectral and angular properties of the resonant X-ray transition radiation and diffracted resonant X-ray transition radiation are investigated. The ratio between the contributions from the diffracted resonant X-ray transition radiation and other types of radiation to the total coherent X-ray radiation flux generated by electrons in periodic structures and crystals is estimated.     

Change in the spatial coherence function at Bragg reflection of an X-ray beam

The influence of coherent properties of an X-ray source (X-ray tube, synchrotron radiation source, free-electron X-ray laser) on the spatial field distribution and the spatial coherence function of this field has been theoretically considered for Bragg reflection from a single crystal.     

Quantum theory of laser cooling: Statistical description of the process dynamics

A dynamic theory of coherent X-ray radiation generated in a periodic layered medium by a relativistic electron multiply scattered by target atoms has been developed. The expressions describing the spectral–angular characteristics of parametric X-ray radiation and diffracted transition radiation are derived. Numerical calculations based on the derived expressions have been performed.     

Sizes of X-ray radiation coherent domains in thin SmS films and their visualization

Technical Physics - The size of X-ray radiation coherent domains (250 ± 20 Å) is determined in a thin polycrystalline SmS film using X-ray diffraction patterns (θ–2θ...     

X-ray surface waves generated by the resonant coherent excitation of relativistic ions in crystals

X-ray ion radiation, caused by resonant coherent excitation (RCE) in a crystal, arises at the crystal-vacuum interface and propagates along the surface, generating a so-called surface wave. The dependence between the surface-wave intensity and the departure angle of characteristic X-ray radiation upon RCE is investigated in a kinematic approximation of diffraction theory. It has been shown that the angular dependence for the intensity of this radiation leaving the crystal surface differs substantially from the radiation intensity inherent to the decay of ion states excited by RCE.     

Controlling the spectral shape of coherent soft X-rays

We demonstrate the generation of arbitrarily shaped spectra of coherent soft X-ray radiation by adaptive control of the driving laser pulse. The selection of both narrow and wide spectral ranges as well as suppression of high-harmonic emission in a selected wavelength region is achieved. Feedback-controlled spectral engineering of coherent soft X-rays paves the way to shaping of soft X-ray pulses and coherent control of electron dynamics in the sub-femtosecond regime.     

Coherent radiation diagnostics of parameters of nanostructures at electron accelerators

The possibility of observing and diagnosing parameters of nanoobjects in a substance by using coherent X-ray radiation arising from the direct interaction of accelerated electrons with the object of interest is discussed. It is analytically shown that analysis of the generated radiation allows the microstructural features of the nanoobject to be studied. To illustrate the main conclusions, coherent radiation generated by relativistic electron scattering on fullerene is considered.     

Fully coherent hard X-ray generation by two-stage phase-merging enhanced harmonic generation

Cascading stages of seeded free electron lasers (FELs) is a promising way to produce fully coherent X-ray radiation. We study a new approach to produce coherent hard X-rays by cascading the recently proposed phase-merging enhanced harmonic generation (PEHG) The scheme consists of one dogleg and two PEHG configurations, and may be one of the leading candidates for the extracted undulator branch in future X-ray FEL facilities. FEL physics studies show that such a scheme is feasible within the present technology and can provide high brightness X-ray radiation pulses with narrow bandwidth and full coherence The radiated peak power at 1 Å wavelength converted from an initial 200 nm seed laser is over 2 GW.