About I08-SXM

X-ray microscopes in general require uniform energy-dependent illumination and especially SXMs are designed as high-flux, moderate energy resolution and broad photon energy range instruments to be operated as highest lateral resolutions. Such requests considerations on high thermal stability and lowest vibrations; a simple X-ray beam preconditioning and low-aberration stigmatic refocusing scheme that preserves the coherence properties of the highly brilliant X-ray source; as well as selecting the right monochromator scheme adapted to the photon energy range. 

At I08-SXM, the X-rays are generated by a 4.5 m long Apple-II helical undulator-type insertion device that provides linear horizontal and vertical polarised X-rays in the 250-4200 eV photon energy range using 1st to 5th harmonics, and 250-1200 eV circular polarised light. The first element in the optical scheme is a beam defining aperture of 1 mm², which adapts the limited acceptance ange of the microprobe forming optic in the end station, and reduces drastically the total power inicident on the first mirror optical components. A first vertically focusing mirror with Au and Ni coatings is operated at 0.7 deg incidence angle and acts as low-band pass filter in order to suppress any spurious and undesired radiation. This mirror collimates also the beam into a SX-700 type plane grating monochromator to be operated over a 250 - 4200 eV photon energy range. Vertically collimated beam geometry allows the plane grating monochromator to be operated in fixed-exit geometry with free selection of the fixed-focus value. A slit system downstream of the first mirror has mainly the purpose of beam cleaning. Stigmatic, low-aberration refocusing of the beam has magnifications of 0.03 in horizontal and 0.2 in vertical considering a source size of 300 micron in horizontal and 50 micron in vertical. This is difficult to achieve by means of toroidal mirror refocusing with optimised magnification of 1, and is thus performed by combination of a horizontally focusing cylindrical mirror and a vertically refocusing elliptical mirror. These two refocusing mirrors generate a stigmatic focus used as exit slit of the monochromator and as secondary source for the microscopes.