TU Berlin

Workgroup of Prof. ThomsenInfrared - lab

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Infrared - lab


Besides the spectroscopy in the near-UV and visible spectral range and as a complementary method to Raman spectroscopy we perform infrared absorption and reflection measurements on crystalline and powder samples.  This is done using a BRUKER IFS 66 v vacuum Fourier-spectrometer.
The Fourier-spectrometer is essentially a Michelson interferometer, which can be illuminated by different infrared sources ( SiC Globar, Hg arc discharge).  The controlled movement of the scanning mirror (M1, see figure)  produces an interferogram signal on the detector, which is modulated by the sample and the device characteristics.  The detector output is digitized, fourier transformed and converted (via the autocorrelation function) to a power spectrum of the measurement. During measurements the interferometer is evacuated to avoid absorption by atmospherical water vapour.
In the far-infrared region ( smaller  700 cm -1) we use an extremly sensitive liquid He cooled Si bolometer as detector, in the mid-ir a liquid nitrogen cooled MCT semiconductor device is applied.  By replacing few parts of the ir-optics the spectrometer is suited for both reflection and absorption spectroscopy. With a He flow cryostate the samples can be cooled to 25 K during measurements. The spectrometer is constructed in a way to support various extentions, detectors etc. so that, for example, the measurement of infrared photoluminescence is possible, as well.
Some technical data :
Spectral range 10 cm-1 ( 1 mm wavelength ! ) to 7000 cm-1
max. resolution 0.25 cm-1


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