Fourier Transform Infrared Spectroscopy

FTIR stands for Fourier transform infrared spectroscopy. We use our FTIR (Bruker Vertex 80) for quickly obtaining transmission and reflection spectra of a wide range of spectral frequencies – from the far infrared (FIR) to the very near infrared (NIR).

Unlike a grating spectrometer, where only a fraction of the scattered light from a grating is detected at a given time, the FTIR records the entire spectral bandwidth at all times. The way it works is that light from a broad band source is split by a beam splitter in two arms of a Michelson type interferometer. One of those beam paths is fixed while the other one can be continuously changed by the spectrometer through a moving mirror. After the light has traveled those two paths, it recombines at the beam splitter, transmits through or reflects off the sample and is detected by a detector. The interference of the light coming from the two beam paths results in an intensity pattern at the detector which depends on the path - or length difference of the two arms in the FTIR. As the spectrometer knows at all times, where the moving mirror is, the recorded intensity vs. position can be transformed into intensity vs. frequency via Fourier Transformation.

Additionally to the typical transmission and reflection configuration, our FTIR is also equipped with an ellipsometry setup which allows us to record how linearly polarized light from a source is affected by the sample.

The FTIR is an incredibly versatile instrument. One can use multiple configurations using internal and external light sources, different modulation schemes in combination with lock-in amplifiers as well as internal and external detectors which opens up many different possibilities for experiments.

Interactive view of the FTIR spectroscopy lab: Click on any image for a view as if you were in our FTIR lab!

A view of the FTIR spectrometer set-up:

A full view of the FTIR system and the surrounding lab area, including the microwave set-up: