Interferometer for Fourier transform infrared spectrometry

An Interferometer, comprising:

• a body supporting stationary parts of the interferometer, a movable scanner assembly, and a motor;
• said stationary parts comprising a radiation source, a collimator arrangement, a beam splitter, a folding mirror, a first terminal mirror, and a second terminal mirror;
• said movable scanner assembly comprising a carrier part drivable by the motor in reciprocating guided movement relative to the body;
• and
• a retro-reflector supported by the carrier part;
• wherein, radiation originating from the radiation source and collimated into a beam of substantially parallel rays will meet an optical surface of the beam splitter at a first oblique angle of incidence to form an incident beam;
• wherein the incident beam will be split into a first, reflected partial beam that will continue along a first arm of the interferometer and a second, transmitted partial beam that will continue along a second arm of the interferometer;
• wherein the incident beam and a surface normal of the beam splitter define a reference plane;
• wherein along the first arm, the scanner assembly is arranged with the retro-reflector positioned to intercept the first partial beam and fold it towards the first terminal mirror such that the first partial beam will meet and be reflected by the first terminal mirror with substantially perfect normal incidence, and the reflected first partial beam will return through the same path along the first arm to the retro-reflector and from there to the beam splitter, where the returning first partial beam will be split into a first reflected portion returning to the collimator and a first transmitted portion continuing on an exit path;
• wherein along the second arm, the folding mirror is positioned to intercept the second partial beam at a second oblique angle of incidence and reflect it to the second terminal mirror, which is positioned to intercept and reflect the second partial beam with substantially perfect normal incidence, such that the reflected second partial beam will return through the same path along the second arm to the folding mirror and from there to the beam splitter, where the returning second partial beam will be split into a second transmitted portion returning to the collimator and a second reflected portion continuing on the exit path;
• and
• wherein the folding mirror and the second terminal mirror are positioned orthogonal to the reference plane and on opposite sides of the exit path, so that a section of the second partial beam from the folding mirror to the second terminal mirror and back to the folding mirror lies in the reference plane and will cross the exit beam twice.