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A spectral line may be observed either as an emission line or an absorption line. Which type of line is observed depends on the type of material and its temperature relative to another emission source. An absorption line is produced when photons from a hot, broad spectrum source pass through a cooler material.
Spectral line shape or spectral line profile describes the form of an electromagnetic spectrum in the vicinity of a spectral line – a region of stronger or weaker intensity in the spectrum. Ideal line shapes include Lorentzian , Gaussian and Voigt functions, whose parameters are the line position, maximum height and half-width. [ 1 ]
In hyperspectral imaging, a complete spectrum or some spectral information (such as the Doppler shift or Zeeman splitting of a spectral line) is collected at every pixel in an image plane. A hyperspectral camera uses special hardware to capture hundreds of wavelength bands for each pixel, which can be interpreted as a complete spectrum.
The two measured spectra can then be combined to determine the material's absorption spectrum. The sample spectrum alone is not sufficient to determine the absorption spectrum because it will be affected by the experimental conditions—the spectrum of the source, the absorption spectra of other materials between the source and detector, and ...
Solar spectrum with Fraunhofer lines as it appears visually. In 1802, English chemist William Hyde Wollaston [2] was the first person to note the appearance of a number of dark features in the solar spectrum. [3] In 1814, Joseph von Fraunhofer independently rediscovered the lines and began to systematically study and measure their wavelengths ...
In true-colour pictures, these nebula have a reddish-pink colour from the combination of visible Balmer lines that hydrogen emits. Later, it was discovered that when the Balmer series lines of the hydrogen spectrum were examined at very high resolution, they were closely spaced doublets. This splitting is called fine structure.
A hot gas under low pressure emits a "bright-line" or emission-line spectrum. A continuous spectrum source viewed through a cool, low-density gas produces an absorption-line spectrum. In the 1860s the husband-and-wife team of William and Margaret Huggins used spectroscopy to determine that the stars were composed of the same elements as found ...
If the instrument is designed to measure the spectrum on an absolute scale rather than a relative one, then it is typically called a spectrophotometer. The majority of spectrophotometers are used in spectral regions near the visible spectrum. A spectrometer that is calibrated for measurement of the incident optical power is called a ...