Fourier Transform Spectrometer
Fourier Transform Spectrometer is installed into a primary vacuum tank (see picture) which lies on pneumatic system to avoid
external vibrations. The room is temperature controlled (▒1K). All systems are computer-driven.
- It is Connes's type interferometer, that is to say stepping mode of cat's eyes.
- Internal modulation synchronized with stepping displacement in order to remove the continuous component of interferometric signal.
- Automatic search of zero path difference.
- Eventual correction of non linearity detector.
- Eventual correction of amplified chain.
- 3m path difference.
- Focus of entrance mirror: 1040mm
- Diameter of entrance diaphragm: from 0.5 to 8mm depending of spectral range and resolution.
- "Cat's eyes"
- Beam splitters.
- Mirror's servosytem
- Mobile mirror of the "cat's eye" type. The cat's eye moves with the help of three actuators (see figure):
- Piezo-ceramics stacks are installed on the convex mirror of the cat's eye:
they are the basic actuators of the servo system (in fact a second stack is installed
on the fixed cat's eye, in opposition). The use of the both stacks allow very precise translations of the order of ▒10Ám.
- A linear motor shift the cat's eye of the order of one millimeter.
- The carriage move with the help of a torque motor along a track. This performs the larger 1.5 m displacement.
- Beam splitter
HeNe laser stabilized on Iodine absorption line.
This computer-controlled laser allows to know and to control the path difference with a precision better than l HeNe/32,
that is to say <10-8m.
More detailed information is given in Reference:
"Reims High Resolution Fourier Transform Spectrometer. Data Reduction for ozone".
J.J. Plateaux, A. Barbe and A. Delahaigue. Spectrochemica Acta, vol. 51A, No.7, pp.1153-1169 (1995).