Fourier-transform spectroscopy

Fourier-transform spectroscopy is a measurement technique whereby spectra are collected based on measurements of the coherence of a radiative source, using the mathematical process of Fourier transformation (FT). In this technique, a spectrum is obtained by first collecting an interferogram of a signal using an interferometer, and then performing a Fourier transform on this interferogram to obtain the spectrum. This method is widely used in various fields such as physics, chemistry, and astronomy for analyzing the spectral characteristics of a sample.

Principles of Operation

Fourier-transform spectroscopy relies on the principle of interference. An interferometer is used to split a single beam of light into two paths, one of which is made to vary in length before the beams are recombined to produce interference patterns. These patterns, or interferograms, contain information about the spectral content of the light source. By applying a Fourier transform to the interferogram, the original spectral information can be reconstructed. This process is advantageous because it allows for the acquisition of high-resolution spectra without the need for a monochromator.

Types of Fourier-transform Spectroscopy

There are several types of Fourier-transform spectroscopy, each based on different configurations of interferometers and applications. The most common types include:

• Fourier-transform infrared spectroscopy (FTIR) - used primarily for identifying organic compounds and analyzing their chemical composition.
• Fourier-transform nuclear magnetic resonance (FT-NMR) - used in nuclear magnetic resonance spectroscopy for determining the structure of organic compounds.
• Fourier-transform mass spectrometry (FTMS) - combines mass spectrometry and Fourier-transform techniques for high-resolution mass analysis.

Applications

Fourier-transform spectroscopy has a wide range of applications across various scientific disciplines. In chemistry, it is used for the analysis of chemical bonds and molecular structures. In astronomy, it helps in the study of the composition of stars and planets. In environmental science, it is applied in monitoring atmospheric gases and pollutants. Additionally, it has significant applications in the fields of pharmacology and biomedical engineering for drug formulation and tissue analysis, respectively.

Advantages and Limitations

The primary advantage of Fourier-transform spectroscopy is its high spectral resolution and fast data acquisition speed. Unlike dispersive instruments, which measure intensity over a range of wavelengths sequentially, Fourier-transform spectroscopy measures all wavelengths at once, which significantly reduces the time required for analysis.

However, the technique also has limitations. It is sensitive to mechanical disturbances and thermal fluctuations, which can affect the accuracy of the interferogram. Moreover, the need for complex mathematical processing of the data requires sophisticated software and computational resources.

See Also

• Spectroscopy
• Interferometry
• Spectral resolution
• Chemical analysis

References

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  Spectrum of a blue flame

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  FTIR interferogram

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  Fourier transform spectrometer