Abstract: 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.

Abstract: The invention relates to an infrared modulator for spectrometer. It comprises a light source (1), a beam splitter (2) for splitting the light from the source into two beams, a first plane mirror (4) for directing the light of the first beam, a second plane mirror (5) for directing the light of the second beam, a first cube corner mirror (7) for turning the light back to the first plane mirror (4), and a second cube corner mirror (6) for turning the light back to the second plane mirror (5). The first and second cube corner mirrors (6, 7) are arranged on a common optic axis to reflect into opposite directions and movable back and forth in the direction of said optic axis. According to the invention, the beam splitter (3) and the first and second plane mirrors (4, 5) are supported by the same support structure formed by one uniform material piece.