Physics: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 [math]\displaystyle{ \Delta\lambda }[/math], and is closely related to the resolving power of the spectrograph, defined as [math]\displaystyle{ R = \frac{\lambda}{\Delta\lambda}, }[/math] where [math]\displaystyle{ \Delta\lambda }[/math] is the smallest difference in wavelengths that can be distinguished at a wavelength of [math]\displaystyle{ \lambda }[/math]. 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.[1]
Doppler effect
The spectral resolution can also be expressed in terms of physical quantities, such as velocity; then it describes the difference between velocities [math]\displaystyle{ \Delta v }[/math] that can be distinguished through the Doppler effect. Then, the resolution is [math]\displaystyle{ \Delta v }[/math] and the resolving power is [math]\displaystyle{ R = \frac{c}{\Delta v}, }[/math] where [math]\displaystyle{ c }[/math] 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.[2] Resolving power, R, is given by the transition wavenumber, wavelength or frequency, divided by the resolution.[3]
See also
References
- ↑ - CRIRES Instrument page at ESO
- ↑ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "resolution in optical spectroscopy". doi:10.1351/goldbook.R05319
- ↑ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "resolving power, R, in optical spectroscopy". doi:10.1351/goldbook.R05322
Further reading
- Kim Quijano, J., et al. (2003), STIS Instrument Handbook, Version 7.0, (Baltimore: STScI)
- Frank L. Pedrotti, S.J. (2007), Introduction to optics, 3rd version, (San Francisco)
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