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SECTION CONTENT
Fourier Transfer Spectrometer
Introduction
Ozone facilities
Experiment set-up
Synthetic spectra
Data reduction
Assignment of lines

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.

GENERAL DESIGN

  • 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.

OPTICAL DESIGN

  • 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.
    • CaF2
    • ZnSe
    • SiO2

MECHANICAL DESIGN

  • 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

WAVELENGTH REFERENCE

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).