Höfler, H.H.HöflerKnothe, M.M.KnotheRiedel, W.J.W.J.RiedelSchmidtke, G.G.Schmidtke2022-03-082022-03-081993https://publica.fraunhofer.de/handle/publica/302785In a derivative spectrometer, a liquid crystal arrangement (32) which is controlled by a control line (34) is located in the plane of an entrance slit of the monochromator (31) which permits light emitted by a light emitting surface (30) to pass through a light-passing window whose position and form is changeable in such a way that firstly, optical errors can be corrected and secondly, that the wavelength of the light leaving the exit slit (19) can be changed at a high modulation frequency in order to implement derivative methods. An arrangement comprising an electron beam tube can also be used instead of a liquid crystal arrangement (32).de608621patent1991-4126547