A spectrometer is an analytical instrument used to measure and analyze the properties of light across a specific portion of the electromagnetic spectrum. It can be used to identify materials, determine their concentration, and analyze the structure of molecules by observing their interaction with light. Spectrometers work by dispersing light into its component wavelengths (spectrum) and measuring the intensity of light at each wavelength.
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A spectrometer measures a signal as a function of a spectral variable. An optical spectrometer commonly separates wavelengths with an optical prism or a diffraction grating, then records the separated light with a photodetector. A spectrograph records many spectral positions together; a monochromator selects a narrow interval for a subsequent measurement.
An entrance slit, collimating optics, dispersing element and focusing optics make a simple grating instrument. Narrowing the slit can distinguish closer spectral lines but admits fewer photons. A lamp with known spectral lines calibrates the wavelength scale, while a blocked input estimates background. Brightness at a detector position becomes a sample optical spectrum only after accounting for the instrument's wavelength-dependent response.