Characterization of the van Cittert monochromator based IR spectrophotometer

摘要

The van Cittert system consists of two identical monochromators coupled together as a subtractive system. The usual narrow slit between the two monochromators is replaced by a wide one and a part of this wide slit is covered by a lamella mounted on a fine resolution translating stage. The wide slit transmits a wide spectral range but the lamella filters out a narrow range like a notch filter. The second monochromater collects and recombines the transmitted radiation at its exit slit. Behind the exit slit and the beam forming elements can the sample be positioned. By the translation fo the lamella the center wavelength of the notch can be shifted over the whole spectral range covered by the wide slit. Carrying out spectrophotometric measurements the total transmitted power is measured at every stop of the lamella. From this array of measurement results the transmittance or the reflectance of the sample can be calculated as a function of the wavelength.