Samiksha Jaiswal (Editor)

Spectral resolution

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The spectral resolution of a spectrograph, or, more generally, of a frequency spectrum, is a measure of its ability to resolve features in the electromagnetic spectrum. It is usually denoted by Δ λ , and is closely related to the resolving power of the spectrograph, defined as

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R = λ Δ λ ,

where Δ λ is the smallest difference in wavelengths that can be distinguished at a wavelength of λ . For example, the Space Telescope Imaging Spectrograph (STIS) can distinguish features 0.17 nm apart at a wavelength of 1000 nm, giving it a resolution of 0.17 nm and a resolving power of about 5,900. An example of a high resolution spectrograph is the Cryogenic High-Resolution IR Echelle Spectrograph (CRIRES) installed at ESO's Very Large Telescope, which has a spectral resolving power of up to 100,000.

Doppler effect

The spectral resolution can also be expressed in terms of physical quantities, such as velocity; then it describes the difference between velocities Δ v that can be distinguished through the Doppler effect. Then, the resolution is Δ v and the resolving power is

R = c Δ v

where c is the speed of light. The STIS example above then has a spectral resolution of 51 km/s.

IUPAC definition

IUPAC defines resolution in optical spectroscopy as the minimum wavenumber, wavelength or frequency difference between two lines in a spectrum that can be distinguished. Resolving power, R, is given by the transition wavenumber, wavelength or frequency, divided by the resolution.

References

Spectral resolution Wikipedia
(Text) CC BY-SA


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