Multilayer mirror for x rays below 190 eV

La/B4C multilayers have been fabricated by magnetron sputtering for use as x-ray mirrors at energies below 190 eV, particularly for detection of boron K and alpha x rays at 183 eV, their performance has been compared with tha t of Mo/B4C multilayers, which are currently the best-performing multilayer s for this energy range. Transmission electron microscopy and synchrotron s oft-x-ray reflectometry were used to study the structural quality of the mu ltilayers and their performance as x-ray mirrors. The results show a signif icant improvement of the peak reflectivity and the spectral purity, indicat ing that La/B4C has a high potential to replace Mo/B4C in many x-ray optica l applications below 190 eV. (C) 2001 Optical Society of America.