Spectral resolution

The spectral resolution or resolving power of say a spectrograph, or, more generally, of a frequency spectrum, is a measure of its power to resolve features, say in the electromagnetic spectrum. It is usually defined by

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R = λ / Δλ,

where Δλ is the smallest difference in wavelengths that can be distinguished, at a wavelength of λ. So, for example, the Space Telescope Imaging Spectrograph (STIS) can distinguish features 0.17 nm apart at a wavelength of 1000 nm, giving it a resolving power of about 5,900.

The spectral resolution can also be expressed in terms of physical quantities, say velocity; then it describes the difference between velocities Δv that can be distinguished through the Doppler effect. Then, the definition is

R = c / Δv,

where c is the speed of light. The STIS example above then has a spectral resolution of 51 kilometres per second.

References

Hatim

1. Kim Quijano, J., et al. (2003), STIS Instrument Handbook, Version 7.0, (Baltimore: STScI)