Project: Fourier Transform Spectrophotometer

At the present time, dispersion spectrometers based on scanning monochromators utilizing diffraction gratings are the most common solution for ultraviolet and visible (UV-Vis) spectroscopy, supplemented with usually less precise CCD-matrix models.

Our project suggests a new design of FTS and a unique method of interferogram processing, which opens up the possibility of the application of the Fourier transform spectroscopy to the visible and even UV spectral range.

This novel approach provides high accuracy of movable mirror positioning in the Michelson interferometer. This allows the expansion of the shortwave boundary of the working range from NIR down to vacuum UV.

Most of modern UV-Vis spectrometers utilize dispersion elements (prisms and diffraction gratings) in order to obtain radiation spectra, whereas
the use of the Fourier Transform spectrophotometers is limited to the NIR and IR range.
Disadvantages of grating based spectrophotometers:

Advantages of Fourier transform spectrophotometers
  • Time of interferogram acquiring and the whole spectrum calculation is comparable with time of registration of a single spectral point in grating spectrometer. As a consequence, Fourier transform spectrometer enhances signal-to-noise ratio comparing to a scanning monochromator (Fellgetts advantage)
  • High throughput due to no slit being used to diaphragm light beam, which also improves signal-to-noise ratio (Jaquinots advantage)
  • High accuracy of wavenumbers over spectrum. Once a device is calibrated for a single wavelength, the calibration over the whole spectrum is achieved
  • High resolution, constant in the whole frequency range
  • Wide spectral range with no high orders typical for grating spectrometer
  • No light scattering at grating
  • High speed (100-1000 times higher than for scanning grating device)
  • Interferogram accumulation mode allows the reduction of the noise and the expansion of the spectrum registration dynamic range
Prospects of the development
  • Working spectral range 4000 through 50000 cm-1 (wavelengths 2500 through 200 nm) with a single photodetector (no switching)
  • Spectral resolution better than 5 cm-1
  • Detectors: Silicon and InGaAs
  • Light source: halogen-deuterium lamp
  • Signal-to-noise ratio in recording electrical channels better than 120 dB (24-bit ADC)
  • Controllable registration rate up to 32 spectra per second (equivalent rate of stepwise scanning 73600 nm/s)
  • Key element is the Michelson interferometer based on two movable mirrors, moving according to harmonic law that provides required phase retardation
  • Active anti-vibration system
  • Autoadjustment