Monochromator

A monochromator is an optical instrument that selects a narrow band of wavelengths from a broader source, typically using a dispersive element and adjustable slits.

Diffraction grating: An optical element with regularly spaced grooves that diffracts light into wavelength-dependent directions. A common dispersive element spreads the source into wavelengths before selection.
Electromagnetic spectrum: The full range of electromagnetic radiation, organized by frequency or wavelength. A monochromator selects a small region from this much broader range.
UV–visible spectroscopy: A technique that measures how ultraviolet and visible light is absorbed or transmitted by a sample. The instrument selects illumination wavelengths for absorbance measurements.
Optical bandpass filter: An optical filter that transmits a wavelength interval while attenuating wavelengths outside it. It selects a band without scanning a dispersive spectrum through an exit slit.
Prism: A transparent optical element that refracts light, with different wavelengths bending by different amounts. Prisms can disperse a source so the monochromator selects one spectral region.
Wavelength: The spatial period of a wave, measured between successive points in the same phase. It is the quantity that a monochromator separates and selects.
Fluorescence spectroscopy: A method that studies light emitted by a substance after it absorbs light at shorter wavelengths. Monochromators select excitation or emitted wavelengths in many fluorescence instruments.
Fourier-transform spectroscopy: Spectroscopy that derives a spectrum from measurements of an optical signal's interference pattern. It acquires spectral information through interferometry rather than monochromator-based dispersion.
Entrance slit: A narrow aperture that defines the incoming light beam's width and angular spread. Its width helps determine how sharply the instrument can separate wavelengths.
Dispersion (optics): The dependence of an optical material's refractive index or an optical system's response on wavelength. Wavelength-dependent deflection makes spectral selection possible.

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