• Krzywinski, J.; Conley, R.; Moeller, S.; Gwalt, G.; Siewert, F.; Waberski, C.; Zeschke, T.; Cocco, D.: Damage thresholds for blaze diffraction gratings and grazing incidence optics at an X-ray free-electron laser. Journal of Synchrotron Radiation 25 (2018), p. 85-90

Open Access Version

The Linac Coherent Light Source (LCLS) is upgrading the machine to high repetition rate and to extended ranges. Novel coatings, with limited surface oxidation, which are able to work at the carbon edge, are required. In addition, high-resolution soft X-ray monochromators become necessary. One of the big challenges is to design the mirror geometry and the grating profile that have high reflectivity (or efficiency) and at the same time can survive the high peak energy of the FEL pulses. For these reasons, we investigated the experimental damage threshold, at 900 eV, of two platinum-coated gratings with different blazed angles. The gratings were tested at 1o grazing incidence. To validate a model for which the damage threshold on blaze grating can be estimated by calculating the damage threshold of a mirror with an angle of incidence identical to the angle of incidence on the grating plus the blaze angle, tests on Pt coated substrates have also been performed. The results confirmed the prediction. We also investigated uncoated silicon, platinum and SiB3 (both deposited on a silicon substrate). In general, the measured damage threshold at the grazing incidence is higher than calculated under the assumption that there is no energy transport from the volume where the photons are absorbed. However, we found that for the case of SiB3 coating, the grazing incidence condition did not increase the damage threshold indicating that the energy transport away from the extinction volume is negligible.