High Resolution Infrared Fourier-Spectrometer IFS 125 HR (Bruker)

IFS 125HR high-resolution Fourier-transform infrared spectrometer manufactured by Bruker Optik GmbH http://www. bruker.ru  (FT spectrometer) is designed to measure optical spectra of transmission and reflection in infrared (IR) range, to determine concentrations of various organic and inorganic substances in solid and liquid phases, etc.


Fig. 1. General view of the IFS 125 HR spectrometer.

The FT spectrometer is based on the double-beam interferometer in which the displacement of an interferometric mirror results in the change in the path-length difference between the interfering beams. The spectrometer is set up as a Michelson interferometer with mirrors in the form of retroreflectors to reduce the influence of external factors. The detected light flux at the output of the interferometer as a function of the path-length difference (the interferogram) represents the Fourier transform of the detected optical spectrum. The spectrum (in the wave-number scale) is determined as a result of the special mathematical calculations (the inverse Fourier transform) of the interferogram.

The interferometer mirror moves linearly in time using the precision mechanism. The exact position of the mirror (the path-length difference in the interferometer) is determined using the reference channel. The zero value of the path-length difference (the main interferogram maximum) is determined from calculations. The FT spectrometer has a table-top design with a separate PC. The FT spectrometer represents a stationary automated device with the modular sealed optics. The sample chamber can be evacuated separately and blew down by air.

The device is equipped with a broad range of optional units and accessories including the 11o specular reflection/transmission unit, single reflection diamond attenuated total reflection (ATR) accessory, multiple ATR unit, parallel-beam transmission unit, integrating gold sphere to measure diffuse reflectance, unit for measuring absolute reflectivities etc. The FT spectrometer is equipped with the Optistat CFv cryostat by Oxford Instruments http://www.oxford-instruments.com with contact cooling and transport of refrigerant vapors. The cryostat allows one to control temperature of the sample under study within the range of 3.8-300 K with an accuracy of 0.1 K.


Fig. 2. The insert to the Optistat CFv cryostat and the regular sample holder.

The measurement process is controlled using the internal controller and PC with the OPUS software. The OPUS software is the all-inclusive program package dedicated to the most efficient usage of the FT spectrometer capabilities. The choice of the sources, optical filters, sample channels and detectors is carried out from the OPUS software without disturbing vacuum in the spectrometer. The device setup, adjustment of its parameters, control of the device operation, Fourier transform of the interferogram, output information processing including the plotting of calibration charts against the reference substances, printing and storage of the analysis results are jumperless. The OPUS software also provides the exchange (transfer) of the data with other programs to prepare documents with the measurement results.

Samples with plane mirror-like surfaces 5-10 mm in diameter are most suitable for IR measurements. The samples for transmission experiments must possess small tapering or one rough surface to exclude interference effects.

Technical data

Spectral range

11000 – 8 cm-1

0.9 – 1250 mm


Better than 0.0063 cm-1

Resolving power

Better than 106

Wavenumber accuracy

Better than 5∙10-7 x wavenumber (absolute)

1∙10-7 (relative)

Photometric accuracy

0.1% T



Scanner speeds

0.16-2.5 cm/s


Fig. 3. IR transmission spectrum of the GaAs/AlGaAs multiperiodic structure obtained using the multiple ATR unit. The inset shows the geometry of the experiment [Yu.A. Aleshchenko, V.V. Kapaev, Yu.V. Kopaev, Yu.G. Sadof’ev, and M.L. Skorikov, Multiperiodic structure for unipolar fountain laser. Quantum Electronics 40 (8), pp. 685-690 (2010)].


Fig. 4. IR reflectivity spectra of the 90 nm thick Ba(Fe0.9Co0.1)2As2 film of superconducting pnictide (Tc = 20 K) on the (La, Sr)(Al, Ta)O3 substrate measured within a broad wavenumber range at various temperatures [Yu.A. Aleshchenko, A.V. Muratov, V.M. Pudalov, E.S. Zhukova, B.P. Gorshunov, F. Kurth, and K. Iida, Observation of Multiple Superconducting Gaps in the Infrared Reflectivity Spectra of Ba(Fe0.9Co0.1)2As2. JETP Letters 94 (9), pp. 719-722 (2011)].


Fig. 5. Reflectivity R(w) of the same film at 5 K normalized to that in the normal state at 30 K. One can notice the pronounced kinks at 23.5 and 29 cm-1. They correspond to the superconducting gaps 2D.