Possibility of X-ray pulse compression using an asymmetric or inclined double-crystal monochromator.

It is shown theoretically that the asymmetric or inclined double-crystal X-ray monochromator may be used for X-ray pulse compression if the pulse is properly chirped. By adjusting the mutual distance of the two asymmetric or inclined crystals it should be possible to achieve even a sub-femtosecond compression of a chirped free-electron laser pulse. The small d-spacing of the crystal enables a more compact scheme compared with the currently used grating compression scheme. The asymmetric cut of the crystal enables the acceptance of a larger bandwidth. The inclined cut has larger tunability.

X-ray collimation by crystals with precise parabolic holes based on diffractive-refractive optics.

Two crystals with precise parabolic holes were used to demonstrate sagittal beam collimation by means of a diffractive-refractive double-crystal monochromator. A new approach is introduced and beam collimation is demonstrated. Two Si(333) crystals with an asymmetry angle of α = 15° were prepared and arranged in a dispersive position (+,-,-,+). Based on theoretical calculations, this double-crystal set-up should provide tunable beam collimation within an energy range of 6.3-18.8 keV (Θ(B) = 71-18.4°). An experiment study was performed on BM05 at ESRF. Using 8.97 keV energy, the beam profile at various distances was measured. The experimental results are in good agreement with theoretical predictions. Owing to insufficient harmonic suppression, the collimated (333) beam was overlapped by horizontally diverging (444) and (555) beams.

Diffractive-refractive optics: (+,-,-,+) X-ray crystal monochromator with harmonics separation.

A new kind of two channel-cut crystals X-ray monochromator in dispersive (+,-,-,+) position which spatially separates harmonics is proposed. The diffracting surfaces are oriented so that the diffraction is inclined. Owing to refraction the diffracted beam is sagittally deviated. The deviation depends on wavelength and is much higher for the first harmonics than for higher harmonics. This leads to spatial harmonics separation. The idea is supported by ray-tracing simulation.

Diffractive-refractive optics: X-ray splitter.

The possibility of splitting a thin (e.g. undulator) X-ray beam based on diffraction-refraction effects is discussed. The beam is diffracted from a crystal whose diffracting surface has the shape of a roof with the ridge lying in the plane of diffraction. The crystal is cut asymmetrically. One half of the beam impinges on the left-hand part of the roof and the other half impinges on the right-hand side of the roof. Owing to refraction the left part of the beam is deviated to the left whereas the right part is deviated to the right. The device proposed consists of two channel-cut crystals with roof-like diffraction surfaces; the crystals are set in a dispersive position. The separation of the beams after splitting is calculated at a distance of 10 m from the crystals for various asymmetry and inclination angles. It is shown that such a splitting may be utilized for long beamlines. Advantages and disadvantages of this method are discussed.

X-ray pulse stretching after diffraction.

The development of ultrashort X-ray pulse sources requires optics that keep the pulse length as short as possible. One source of pulse stretching is the penetration of the pulse into a crystal during diffraction. Another source is the inclination of the intensity front when the diffraction is asymmetric. The theory of short X-ray pulse diffraction has been well developed by many authors. As it is rather complicated, it is sometimes difficult to foresee the pulse behavior (mainly stretching) during diffraction in various crystal arrangements. In this article, a simple model is suggested that gives a qualitatively similar shape to the diffracted pulse which follows from exact theory. It allows proposal of what experimental arrangement is optimal to minimize the pulse stretching during diffraction. First, the effect of pulse stretching due to penetration into a crystal surface is studied. On the basis of this, the pulse profile change during diffraction by two crystals, either symmetric or asymmetric, is predicted.

Diffractive-refractive optics: X-ray collimator.

Diffractive-refractive optics are x-ray focusing monochromators based on the diffraction on profiled crystal surface. Diffraction on longitudinal parabolic groove machined in crystal surface forms a sagittaly focused synchrotron radiation beam. Such kind of monochromator may be realized as a crystal with parabolic hole, where the beam is diffracted on the inner wall of the hole. Two such asymmetrically cut crystals set into antiparallel position, creating a dispersive (+,-,-,+) arrangement, form a sagittaly focusing x-ray monochromator which should be practically aberration-free. The focusing properties of such kind of monochromator are discussed in detail and it is shown for the first time that it can be used not only for focusing but also for creating highly parallel monochromatic beam in the broad region of the Bragg angles. This device with parabolic hole has not been tested experimentally yet.

Ray-tracing analysis of diffractive-refractive X-ray optics.

Ray-tracing simulations of mistuned sagittal diffractive-refractive X-ray lenses (DRXL) are presented. In this article, firstly the characteristic aberrations for various types of crystal misalignments within one-crystal and four-crystal DRXLs are considered, and the sensitivity of such an optical system to the mutual misalignment of its components is discussed. The simulations reveal that a DRXL is not too sensitive to the adjustment of its components. In the second part of this article the performance of such lenses with ideal and approximate profiles is examined. Comparative analysis of parabolic and cylindrical DRXLs showed that, in the case when the linear source size is comparable with the acceptance of the lens, the performances of parabolic and cylindrical DRXLs are practically the same.