spectral resolution

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 $\Delta\lambda$ , and is closely related to the resolving power of the spectrograph, defined as

$R = \frac{\lambda}{\Delta\lambda},$

where $\Delta\lambda$ is the smallest difference in wavelengths that can be distinguished at a wavelength of $\lambda$ . 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.[http://www.eso.org/instruments/crires/ - CRIRES Instrument page at ESO]

Doppler effect

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

$R = \frac{c}{\Delta v},$

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.{{GoldBookRef|title=resolution in optical spectroscopy|file=R05319}} Resolving power, R, is given by the transition wavenumber, wavelength or frequency, divided by the resolution.{{GoldBookRef|title=resolving power, R, in optical spectroscopy|file=R05322}}

spectral resolution

Doppler effect

IUPAC definition

See also

References

Further reading