wavelengthresolving

Wavelength resolving, often referred to as spectral resolution, is the ability of an optical instrument to distinguish between two close wavelengths of light or other electromagnetic radiation. It describes how finely an instrument can separate spectral features such as emission or absorption lines. The key metric is the resolving power R = λ/Δλ, where Δλ is the smallest difference in wavelength that can be distinguished at wavelength λ. A higher R indicates finer distinction between nearby wavelengths.

In dispersive instruments such as grating or prism spectrometers, Δλ depends on the dispersive power of the element, the optical design, and the width of the entrance slit, as well as how the spectrum is sampled by the detector. In practice, the instrument function or line spread function determines whether two lines are resolved; the Rayleigh criterion is often used as an idealized limit in diffraction-limited systems.

Resolution is wavelength-dependent and may vary across the spectral range of an instrument. Tradeoffs exist between resolution, signal-to-noise, and spectral coverage: increasing dispersion or narrowing the slit improves resolution but reduces light throughput. Detector pixel size and readout also constrain Δλ through sampling.

Applications span chemistry, physics, astronomy, and remote sensing, where resolving power determines the ability to identify species, measure Doppler shifts, or detect fine spectral features. Common laboratory spectrometers reach modest to high resolving powers (thousands to tens of thousands), while high-resolution instruments used in astronomy can exceed 100,000. See also spectral resolution, diffraction, spectrometer.