Coherent X-rays at MAMI

Abstract

Abstract. Coherent radiation in the range from soft X-rays up to hard X-rays, produced by the lowemittance electron beam of MAMI, can be used for various applications. Novel types of interferometers have been developed for the measurement of the complex index of refraction of thin self-supporting foils. For the vacuum ultraviolet and soft X-ray region the interferometer consists of two collinear undulators, and a grating spectrometer. A foil placed between the undulators causes a phase shift and an attenuation of the oscillation amplitude. The complex index of refraction has been measured at the L 2,3-absorption edges of nickel. A novel method is described for the measurement of the X-ray magnetic circular birefringence. For the hard X-ray region the interferometer consists of two foils at which the 855 MeV electron beam produces transition radiation. Distinct interference oscillations have been observed as a function of both, the photon emission angle and the distance between the foils. The refractive index decrement δ(ω) of a 2 µm thick nickel sample foil has been measured at X-ray energies around the K absorption edge at 8333 eV and at 9930 eV with an accuracy of better than 1.5 %. The line width of parametric X radiation (PXR) was measured in backward geometry with a Si single-crystal monochromator. Upper limits of the line width of 42 meV, 50 meV, and 44 meV, have been determined for the (333), (444) and (555) reflections at photon energies of 5932 eV, 7909 eV, and 9887 eV, respectively. Small angle scattering of the electrons in the crystal leads to a stochastic frequency modulation of the exponentially damped wave train which results in the line broadening. To elucidate the quest if the production of PXR is a kinematical or a dynamical process the radiation from silicon single-crystal targets, emitted close to the electron direction, has been studied. The observed interference structures and the narrow-band radiation in forward direction shows that PXR is produced in a dynamical process. .Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity) -41.60.-m Radiation by moving charges -41.50.+h X-ray beams and X-ray optics PACS.

Miniature magnetic devices for laser-based, table-top free-electron lasers

“…The electron beam energy was set to 705 and 405 MeV as these energies lead to a radiation energy of E n 860 eV for the fundamental and the third harmonic, respectively. This photon energy coincides with two L-absorption edges of a thin Ni foil (E L2 854:7 eV, E L3 871:9 eV [23]) providing the required high-resolution online calibration of the linewidth of the undulator radiation. Electron beam focusing was optimized for a minimum linewidth taking into account beam divergence as well as the analytical off-axis field distribution of an undulator.…”

“…It was read out by an efficient x-ray CCD camera (pixel size 13 13 m 2 ) some 6.7 m further downstream [11,23]. Succeeding the first experiment, the undulator was carefully retuned to the most critical minimum gap height of g 1:5 mm (K 0:45).…”

Parametric X-ray radiation in the Smith-Purcell geometry for non-destructive beam diagnostics

“…For the numerical considerations we employ the characteristics of the Mainz microtron MAMI [13,14]. As a result for the radiation wavelength λ = 3 × 10 −8 cm, the emittance = 3 × 10 −7 cm and γ = 2 × 10 3 the coherent length reaches…”

“…First of all, we compare the relative contributions into the total radiation intensity N PXR−SPG from the parts of the electron beam that are moving in crystal and in vacuum (pure SP radiation) respectively, analogously to the ideal case. According to the qualitative estimation (14) and Eq. (63) of the ideal case the Smith-Purcell radiation can be significant when the beam propagates close to the crystal surface (a 0 is small) and possesses a small transversal width ∆a.…”

Novel optical interferometry of synchrotron radiation for absolute electron beam energy measurements

“…The method is based on interferometry with two spatial separated light sources driven by relativistic electrons [17][18][19]. The basic idea will be explained by means of the schematic drawing shown in Fig.…”