A simple spherical grating by-pass monochromator dedicated to soft x-ray emission spectroscopy

PoLIFEMo (Polarized Light Improved Flux Efficiency Monochromator) is the name of a spherical grating monochromator designed with the purpose of maximizing the photon intensity on a sample. The device is mainly conceived to improve performances of an x-ray emission spectrometer, whose limiting factor is often the counting rate. By keeping the exit slit fixed, it is possible to let a small spot size (similar to 35 mu m vertically) on a sample placed just near the exit slit, without the need of postgrating refocusing optics. No entrance slit is used because of the low beam divergence, allowing the use of a virtual source in a converging beam geometry. The tuning of the output energy is done by translating and pitching the spherical grating. The resolving power is higher than 1000 over the whole energy range (500-1500 eV). A detailed analysis of the optical performances is given, mostly in comparison with the Dragon-type monochromator, The actual realization of the device is described, together with the specific motivations and the experimental performances. PoLIFEMo has been installed on beam line ID12B at the European Synchrotron Radiation Facility since July 1996. (C) 1998 American Institute of Physics.