Broadband FTIR Spectroscopy

To measure the reflectivity and transmission of a material we employ a Bruker Vertex 80v Fourier transform infrared spectrometer. Originally invented by A. Michelson this interferometer works by splitting the light into two paths before recombining them and sending the light to the sample. One path length is fixed and the other moving. By measuring the intensity of the light versus position of the mirror, one can quickly determine the intensity versus frequency via a fast Fourier transform. With the FTIR we can measure a materials transmissivity and/or reflectivity from 0.8 meV (10 cm-1) to 4.3 eV (35,000 cm-1) with 8 µeV (0.07 cm-1) resolution. These experiments are performed in ultrahigh vacuum (10-8 mBarr) at temperatures ranging from 4 K to 420 K.