Fourier-Transform Infrared Spectroscopy (FTIR)
The FTIR is a Michelson interferometer used to measure infrared absorption of a sample. Our Bruker IFS 66v can be used in the near, mid and far IR, providing absorption spectra over an extremely wide spectral range (1-500um), using a combination of alkakli-halide and mylar beam splitters and InSb, HgCdTe (MCT), and bolometer detectors for detection.
The FTIR sends a collimated thermal source with a broad emmision spectrum through a sample and into a Michelson interferometer. The instrument sweeps the mirror in one arm of the interfermeter at a constant rate. An interferogram is produced by measuring the intensity at the output of the interferemeter as a function of time. For low-light measurements the interferogram can be built up by repeatedly stepping the mirror and collecting a single data point.
The frequency spectrum is obtained by taking the Fourier transform of the interferogram and subtracting it from a reference spectrum taken with no sample. Our FTIR is mainly used to measure FIR intraband absorption spectra of coupled quantum well and dots, but we can also use it to measure the thickness of wafers by measuring the spacing between Fabry-Perot fringes.
There are many tips and tricks on our particular machine, a Bruker IFS 66v.
In transmission THz spectroscopy experiments, changes in the optical absorption/transmission, or resonant scattering due to THz irradiation are measured. We have used this technique to investigate collective dynamics of electrons in quantum wells, and recently, as a technique for Optical Phonon Transit Time Resonance in GaN.