# Diffraction (physics)

the diffraction or diffraction is the “diverson” from waves (like light - and other electromagnetic waves, water or acoustic waves) at an obstacle. With diffraction features itself the wave in the geometrical shadow region of the obstacle (gap, lattice can , Catch mirror etc.) spread. To the diffraction it comes by emergence of new waves along in accordance with a wave front the Huygens principle. These can lead by overlay to interference features.

## diffraction from light waves

to ways of the Wellennatur of the light deviates his material behavior partly strongly from that one, which expect the geometrical opticswould leave. Like that the sharpness of a photo is limited by the size of (numeric aperture) of the lens with the photography diffraction-causes. Z is very remarkable. B. the occurrence of colors of the rainbow on the back of CDs (diffraction of same angles) or thatSquint-learn a thin oil film on water (diffraction of same thickness). The physical model for diffraction is the Huygens principle. For the computation of diffraction patterns the Kirchhoff diffraction integral is used, whose two border lines are the Fresnel diffraction (near field approximation) and the Fraunhofer diffraction (far field approximation). ThoseOverlay of the elementary waves can to mutual reinforcement (constructional interference) or to mutual weakening (destructive interference) or extinction to lead, see also with Gangunterschied.

In contrast to it the refraction of waves in media with different refractive index without attention that can Wellennatur of the light by the geometrical optics to be described. With the wave optics one can describe both refraction and diffraction, while the geometrical optics cannot describe the diffraction.

Diffraction can be among other things well observed, if geometrical structures oneRole play, whose size is comparable with the wavelength of the used waves.

### examples of diffraction of light

interference at the double gap
interference at the double gap
a wave meets on two closely together lying columns, behind it overlay the two partial jets. Ita set of interference maxima results with the characteristic that the distance difference of the two partial jets is an integral multiple of the wavelength.
Diffraction at the single gap
one divides a light bundle, which is diverted at a single gap in a certain direction into thoughts,in two halves, these two portions of the light bundle can overlay constructionally or destructively. At a gap so again a set of diffraction maxima results.

### Light and Roentgen diffraction at the lattice

• optical lattice: Are arranged in regular intervals many column, results a set of diffraction reflexes, whose arrangement corresponds to those, which one expects with a double gap with the same distance. With increasing amount of thatSingle column the reflexes become however ever sharper lines. Since the situation of the reflexes depends on the wavelength of the light, one can use optical lattices for the separation of different wavelengths. That is in the Monochromator and with the spectroscopy the case. Itin practice very frequently regular arrangements are used of reflecting and not reflecting strips as reflecting gratings. The back CD works similarly!
• Roentgen diffraction: This is used in crystallography for determining and measuring crystal lattices. The wavelength that X-ray is comparable with the lattice spacings in the crystal, and the crystal lattice works as multidimensional optical lattice.

## diffraction of further kinds of wave and its use

in principle apply for regularities, which apply to the diffraction of light waves, also to other wave features.Even if they are hardly to be compared in their effects.

• In the acoustics:
The diffraction of sound is important for the computation of noise zones.
• In particle physics
one concerns oneself among other things with the electron diffraction.
• In the seismology
Since seismic waves (seismic waves) at the surface and in the underground reproduce themselves, its diffraction can serve for the investigation of many structures between earth's crust and earth core. One knows z. B. profilweise laid out geophones as kind diffraction grating regard and from thatOverlay of artificial quake waves the process of coal seams determine. On the other hand the waves of earthquakes become z. B. at the border between Earth's mantle and core bent, with which for a long time the shell structure of the earth is investigated.
• There
are water waves in the water interesting overlaysof waves (quay wall, motorboats etc.). One can use similar effects for the detection of structures under water.
• In the quantum theory each particle has also in principle wave characteristics, thus is possible, although experimentally with difficulty accessible a diffraction of particle beams. Itz could. B. the diffraction by jets from C 60 molecules in the experiment to be proven.