Experimental determination of the diffraction efficiency and high-order suppression of gratings for synchrotron radiation

Abstract

We present new experimental data on diffraction efficiency measurements on gratings for the first undulator beamlines at BESSY II. The measured data will be compared with results from electromagnetic theory. A good suppression of higher orders, i.e. the sum of higher orders from higher energies which are diffracted into the same angle as the first order, has been an important point during the design process of the beamlines at BESSY II. For this purpose lamellar grating structures have been optimized and specified. The measurements were carried out with a triple axis vacuum diffractometer at the BESSY I PM 4 beamline in an energy range from 70 to 1200 eV. We measured the diffraction efficiencies of the first order and the corresponding second and third order at discrete energies E, i.e. second and third order efficiency at 2E and 3E respectively. To improve the accuracy of the measurements, the higher orders from the PM 4 beamline had to be taken into account. We used a calculation scheme starting at the highest energy, in which the diffraction efficiency of the grating under test and the higher orders from the monochromator have been evaluated simultaneously. The calculated higher orders of the monochromator were then recursively used as input for the calculation at lower energies. The gratings were measured at different angular settings, hence enabling different degrees of high order suppression. It was determined, that with appropriate angular settings, the higher orders of monochromator gratings can be significantly reduced.