Definition of diffraction grating

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Photonics Dictionary

diffraction grating

A diffraction grating is an optical component consisting of a surface with a periodic structure of equally spaced, parallel grooves or rulings. These rulings act as an array of closely spaced slits or reflective elements that cause incoming light to diffract or spread out into its component wavelengths.

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When monochromatic light (light of a single wavelength) illuminates a diffraction grating, the grooves cause the light to interfere constructively and destructively, resulting in a pattern of bright and dark bands known as a diffraction pattern or spectral pattern. The angles at which these bands appear depend on the wavelength of the incident light and the spacing between the grooves on the grating.

Diffraction gratings are characterized by parameters such as:

Groove density: The number of grooves per unit length, usually specified in lines per millimeter (l/mm) or lines per inch (l/in).

Grating period: The distance between adjacent grooves, typically measured in micrometers (µm) or nanometers (nm).

Blaze angle: The angle at which the grooves are cut or ruled into the grating surface, affecting the intensity distribution of the diffracted light.

Diffraction gratings can be classified into two main types based on their operating principle:

Transmission gratings: These gratings are transparent, with the grooves typically ruled or etched into a glass or plastic substrate. Transmission gratings are commonly used in spectroscopy, where they disperse light into its component wavelengths for analysis.

Reflection gratings: In reflection gratings, the grooves are typically ruled or replicated onto a reflective surface, such as a metal-coated substrate. Reflection gratings are widely used in applications such as laser systems, telecommunications, and optical instruments.

Diffraction gratings have numerous applications in various fields, including:

Spectroscopy: Dispersing light into its spectral components for analysis of atomic and molecular properties.

Astronomy: Spectrographs use diffraction gratings to analyze the light emitted or reflected by celestial objects.

Laser systems: Gratings are used for wavelength selection, tuning, and dispersion in lasers and laser-based systems.

Optical communications: Gratings are employed in wavelength division multiplexing (WDM) systems for transmitting and receiving multiple optical signals over a single optical fiber.

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