We describe an instrument designed for studying the electronic structure of bulk, surface, and deep solid–solid interface. The analysis is made by soft-x-ray emission spectroscopy induced by electron bombardment. The target is placed under ultrahigh vacuum and can be prepared and treated in situ. High resolution is achieved both as concerns the photon energy and the electron-beam energy. Tests have been made in the dispersive mode and in the characteristic isochromat mode. In both cases experimental resolution is in good agreement with the expected one.

The light reflected by an uncoated Fabry-Perot etalon presents dark rings which give a very sensitive measurement of the variations of the return optical path in the etalon. By measuring the diameters of these rings as a function of the etalon temperature T, we get a sensitive measurement of the derivative dn/dT of the index of refraction n. We have made this experiment with a fused silica etalon and we have achieved a 2% relative uncertainty on dn/dT, comparable to the uncertainty of the best experiments.