How does a FTIR machine operate?

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SUMMARY

The FTIR (Fourier Transform Infrared) machine operates using a Michelson interferometer, which features a moving mirror to create interference patterns from a broadband source. The detector captures the intensity of radiation, converting it into an interferogram, which is a time-domain representation of the intensity variations. Importantly, the interference does not yield a single resultant frequency; instead, each frequency corresponds to a sine wave in the time domain. The laser present in the FTIR is utilized for optical alignment, ensuring accurate measurements.

PREREQUISITES
  • Understanding of Michelson interferometer principles
  • Knowledge of Fourier transforms and their applications
  • Familiarity with broadband radiation sources
  • Basic concepts of optical alignment techniques
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  • Study the operation of Michelson interferometers in detail
  • Learn about Fourier Transform techniques in spectroscopy
  • Explore the role of broadband sources in FTIR spectroscopy
  • Investigate optical alignment methods in laboratory settings
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Researchers, chemists, and laboratory technicians involved in spectroscopy and material analysis will benefit from this discussion, particularly those seeking to deepen their understanding of FTIR operation and principles.

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I know the basics about the interferometer and how this causes intereference patterns in a broadband spectrum to occur but I need to clarify a few things and I can't find the answer in any textbook:

1. The detector receives information on the intensity of radiation being received and I have often read about the interferometer being able to simutaneousily sample the entire broadband spectrum range - I don't really understand this because when the waves interfere will there not being one resultant frequency at a particular wavelength?
2 Is the laser in the FTIR machine there present for calibration purposes?

Please help if you can, I am finding it quite hard to get around some concepts
Thanks
 
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I don't really understand this because when the waves interfere will there not being one resultant frequency at a particular wavelength?
Frequency is the property of the source. The interference does no affect the source.
So there is no resultant frequency in the interference pattern.
 
The FTIR spectrometer works with a Michelson interferometer. It has a moving mirror and the intensity of the radiation of a broad-band source is converted to the interferogram - resultant intensity of the interfering rays coming from two arms one with constant length, the other with a length x(t) changing in time. One frequency in the spectrum corresponds to a sine wave in x or t. The interferogram and the original spectrum are Fourier transforms of each other.

The laser in the apparatus is for the optical alignment.

ehild
 

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