Diffraction grating

In <a href="/facts/Optics/p0vq4S1T">optics</a>, a diffraction grating is an optical <a href="/facts/Grating/YMV3Ioku">grating</a> with a periodic structure that <a href="/facts/Diffraction/Mk80xXHT">diffracts</a> light, or another type of <a href="/facts/Electromagnetic_radiation/Ynx7ujCW">electromagnetic radiation</a>, into several beams traveling in different directions (i.e., different diffraction angles). The emerging coloration is a form of <a href="/facts/Structural_coloration/vg3zYCd9">structural coloration</a>. The directions or diffraction angles of these beams depend on the wave (light) <a href="/facts/Angle_of_incidence_(optics)/DTaCjhTU">incident angle</a> to the diffraction grating, the spacing or periodic distance between adjacent diffracting elements (e.g., parallel slits for a transmission grating) on the grating, and the <a href="/facts/Wavelength/kcJU0ymz">wavelength</a> of the incident light. The grating acts as a <a href="/facts/Dispersion_(optics)/cUdHnYXz">dispersive</a> element. Because of this, diffraction gratings are commonly used in <a href="/facts/Monochromator/vagojlBb">monochromators</a> and <a href="/facts/Spectrometer/IqRE8xaQ">spectrometers</a>, but other applications are also possible such as optical encoders for high-precision motion control and <a href="/facts/Wavefront/5XVoVtDQ">wavefront</a> measurement.
For typical applications, a <a href="/facts/Reflection_(optics)/BhcjDs79">reflective</a> grating has ridges or rulings on its surface while a transmissive grating has transmissive or hollow slits on its surface. Such a grating modulates the amplitude of an incident wave to create a diffraction pattern. Some gratings modulate the phases of incident waves rather than the amplitude, and these types of gratings can be produced frequently by using <a href="/facts/Holography/4J1gW0M6">holography</a>.
<a href="/facts/James_Gregory_(astronomer_and_mathematician)/W0aza1VS">James Gregory</a> (1638–1675) observed the diffraction patterns caused by a <a href="/facts/Feather/sxbf96nF">bird feather</a>, which was effectively the first diffraction grating (in a natural form) to be discovered, about a year after <a href="/facts/Isaac_Newton/4L7gTncN">Isaac Newton</a>'s <a href="/facts/Prism_(optics)/eodBFF70">prism</a> experiments. The first human-made diffraction grating was made around 1785 by <a href="/facts/Philadelphia/2bFFCCTU">Philadelphia</a> inventor <a href="/facts/David_Rittenhouse/5dAlKDPd">David Rittenhouse</a>, who strung hairs between two finely threaded screws. This was similar to notable German physicist <a href="/facts/Joseph_von_Fraunhofer/1dWvIByM">Joseph von Fraunhofer</a>'s wire diffraction grating in 1821. The principles of diffraction were discovered by <a href="/facts/Thomas_Young_(scientist)/X4RtR47L">Thomas Young</a> and <a href="/facts/Augustin-Jean_Fresnel/jb64tyGc">Augustin-Jean Fresnel</a>. Using these principles, Fraunhofer was the first to use a diffraction grating to obtain <a href="/facts/Spectral_line/HuI4Bj5f">line spectra</a> and the first to measure the wavelengths of spectral lines with a diffraction grating.
In the 1860s, state-of-the-art diffraction gratings with small groove period (d) were manufactured by <a href="/facts/Friedrich_Adolph_Nobert/TuA1FGrh">Friedrich Adolph Nobert</a> (1806–1881) in <a href="/facts/Greifswald/BLuvVmTo">Greifswald</a>; then the two Americans Lewis Morris Rutherfurd (1816–1892) and William B. Rogers (1804–1882) took over the lead. By the end of the 19th century, the concave gratings of <a href="/facts/Henry_Augustus_Rowland/Fmj2U2AW">Henry Augustus Rowland</a> (1848–1901) were the best available.
A diffraction grating can create "<a href="/facts/Rainbow/rBvLyu3u">rainbow</a>" colors when it is illuminated by a wide-spectrum (e.g., continuous) light source. Rainbow-like colors from closely spaced narrow tracks on optical data storage disks such as CDs or DVDs are an example of light <a href="/facts/Diffraction/Mk80xXHT">diffraction</a> caused by diffraction gratings. A usual diffraction grating has parallel lines (It is true for 1-dimensional gratings, but 2 or 3-dimensional gratings are also possible and they have their applications such as wavefront measurement), while a CD has a spiral of finely spaced data tracks. Diffraction colors also appear when one looks at a bright point source through a translucent fine-pitch umbrella fabric covering. Decorative patterned plastic films based on reflective grating patches are inexpensive and commonplace. A similar color separation seen from thin layers of oil (or gasoline, etc.) on water, known as <a href="/facts/Iridescence/ykc1opK8">iridescence</a>, is not caused by diffraction from a grating but rather by <a href="/facts/Thin_film_interference/UScpq8NL">thin film interference</a> from the closely stacked transmissive layers.

Diffraction grating open-in-new

Diffraction grating