According to an aspect, there is provided a spectrometer comprising a first and second enclosed volumes. The second enclosed volume is formed by an absorption cell for containing a sample gas. The first enclosed volume of the spectrometer comprises an interferometer with a source of electromagnetic radiation, a first focusing mirror adapted to focus electromagnetic radiation received from the interferometer to the absorption cell, a second focusing mirror adapted to focus electromagnetic radiation received from the absorption cell and a detector adapted to detect electromagnetic radiation focused by the second focusing mirror. Moreover, the spectrometer comprises a main frame plate on which elements in the first enclosed volume are mounted and which is fixed to the absorption cell arranged on an opposing side of the main frame plate.