FTIR is a method of molecular spectroscopy and one of the most important application fields of He-Ne lasers. For FTIR an infrared light source is used to illuminate a sample.
A part of the light is absorbed. The spectrum of the light which passes the sample is characteristic for the molecules and chemical compounds in the sample. So, a sample can be scanned for many different components leaving there “spectroscopic fingerprints”. The method is used in laboratories e.g. for inspection of food or pharmaceutical products as well in industrial environmental to observe the quality of products or environmental parameters.
The heart of the spectrometer is a Michelson interferometer formed by a moving and a reference mirror. For each position of the moving mirror a signal is measured at a detector. All these data form a so called interferogram which is finally translated into the full spectrum by a computer based Fourier transform algorithm. The light source of the interferometer is a He-Ne laser which measures exactly the position if the moving mirror.
He-Ne lasers are especially suited for FTIR because of their
- excellent beam quality
- long coherence length
- unbeatable price performance ratio