The speckle effect is observed when radio waves are scattered from rough surfaces such as ground or sea, and can also be found in ultrasonic imaging.

When lasers were first invented, the speckle effect was considered to be a severe drawback in using lasers to illuminate objects, particularly in holographic imaging because of the grainy image produced.

It was later realized that speckle patterns could carry information about the object's surface deformations, and this effect is exploited in holographic interferometry and electronic speckle pattern interferometry.

The speckle effect is also used in stellar speckle astronomy, speckle imaging and in eye testing using speckle.

For many years telescope performance was limited by this effect, until the introduction of speckle interferometry and adaptive optics provided paths to remove this limitation.

The speckle pattern which is observed when laser light falls on an optically rough surface is also a diffraction phenomenon.

The speckle pattern which is seen when using a laser pointer is another diffraction phenomenon.

An example of deleterious mechanically induced modulation is speckle noise created in a multimode fiber by an imperfect splice or imperfectly mated connectors.

This is a subjective speckle pattern.

A speckle pattern is an intensity pattern produced by the mutual interference of a set of wavefronts.

A less familiar example of speckle is the highly magnified image of a star through imperfect optics or through the atmosphere ( see speckle imaging ).

A speckle pattern can also be seen when sunlight is scattered by a fingernail.

When we observe an illuminated surface, we detect the average energy of the light at the surface ; thus the brightness of a given point on a surface which has been illuminated by a set of random scatterers with a single frequency, is constant over time, but varies randomly from point to point, i. e. it is a speckle pattern.

If light of low coherence ( i. e. made up of many wavelengths ) is used, a speckle pattern will not normally be observed, because the speckle patterns produced by individual wavelengths have different dimensions and will normally average one another out.

When an image is formed of a rough surface which is illuminated by a coherent light ( e. g. a laser beam ), a speckle pattern is observed in the image plane ; this is called a “ subjective speckle pattern ” – see image above.

It is called " subjective " because the detailed structure of the speckle pattern depends on the viewing system parameters ; for instance, if the size of the lens aperture changes, the size of the speckles change.

# Long exposure images of these changing speckle patterns result in a blurred image of the point source, called a seeing disc

Unfortunately, the phase differences between adjacent image picture elements (" pixels ") also produce random interference effects called " coherence speckle ", which is a sort of graininess with dimensions on the order of the resolution, causing the concept of resolution to take on a subtly different meaning.

This setup is used to avoid speckle noise form being generated from interference of the two waves within the scattering medium, which would occur if they were both propagated through the medium.

Speckle contrast reduction is essentially the creation of many independent speckle patterns, so that they average out on the retina / detector.

The fact that many of the speckle imaging methods have multiple names results largely from amateur astronomers re-inventing existing speckle imaging techniques and giving them new names.

An analogy with water waves may help to understand the speckle phenomenon.

Image: Zeta bootis short exposure. png | Typical short-exposure image of this binary star from the same dataset, but without using any speckle processing.

One more recent type of speckle interferometry called speckle masking involves calculation of the bispectrum or closure phases from each of the short exposures.

When laser light which has been scattered off a rough surface falls on another surface, it forms an “ objective speckle pattern ”.

The " size " of the speckles is a function of the wavelength of the light, the size of the laser beam which illuminates the first surface, and the distance between this surface and the surface where the speckle pattern is formed.

Rotating diffusers — which destroys the spatial coherence of the laser light — can also be used to reduce the speckle.

While it may provide less anatomical detail than techniques such as CT or MRI, it has several advantages which make it ideal in numerous situations, in particular that it studies the function of moving structures in real-time, emits no ionizing radiation, and contains speckle that can be used in elastography.

# It causes the images of point sources ( such as stars ), which in the absence of atmospheric turbulence would be steady Airy patterns produced by diffraction, to break up into speckle patterns, which change very rapidly with time ( the resulting speckled images can be processed using speckle imaging )

In the 1980s methods were developed which allowed images to be reconstructed interferometrically from these speckle patterns.

Another issue is the presence of substantial speckle noise which lowers the overall signal-to-noise ratio of particle images.

In one technique called shift-and-add ( also called image stacking ), the short exposure images are lined up by the brightest speckle and averaged together to give a single output image.

By shining a laser ( whose smooth wavefront is an excellent simulation of the light from a distant star ) on a surface, the resulting speckle pattern can be processed to give detailed images of flaws in the material.

If a photographic plate or another 2-D optical sensor is located within the scattered light field without a lens, a speckle pattern is obtained whose characteristics depend on the geometry of the system and the wavelength of the laser.

A laser shining into the mixture produces a speckle pattern that results from the motion of the particles.

Laser speckle on a digital camera image from a green laser pointer.

In the output of a multi-mode optical fiber, a speckle pattern results from a superposition of mode field patterns.

If the relative modal group velocities change with time, the speckle pattern will also change with time.

However, speckle patterns can be observed in polychromatic light in some conditions.

Jazz is good not only because it promotes wholeness but because of its decided sexual effect.

The general effect is tragic.

He is a dreamer of the good society with a plan to put into effect, and he is an individual craftsman with something to make for himself and the people of his time.

The interesting thing about Mr. Lyford's approach, and the approach of the contributors to The Agreeable Autocracies ( Oceana Publications, 1961 ) to the situation of American civilization, is that it is concerned with comprehending the psychological relationships which are having a decisive effect on American life.

If `` Jack the Courtier '' is really to be taken as Swift, the following remark is obviously Steele's comment on Swift's change of parties and its effect on their friendship: `` I assure you, dear Jack, when I first found out such an Allay in you, as makes you of so malleable a Constitution, that you may be worked into any Form an Artificer pleases, I foresaw I should not enjoy your Favour much longer ''.

In this domain the simple fact of coexistence in the same local, national, and world community is enough to guarantee that we cannot refrain from having some effect, large or small, upon Gentile-Jewish relations.

In the calm which follows the reading of a poem, for example, is the effect produced by the enforced quiet, by the musical quality of words and rhythm, by the sentiments or sense of the poem, by the associations with earlier readings, if it is familiar, by the boost to the self-esteem for the semi-literate, by the diversion of attention, by the sense of security in a legitimized withdrawal, by a kind license for some variety of fantasy life regarded as forbidden, or by half-conscious ideas about the magical power of words??

He is, rather, concerned with the effect on society and he wants the poets to join his fight for justice.

In Krutch's view, this is one way to show how literature may be moral in effect without employing the explicit methods of a moralist.

If Krutch is correct, tragedy may have quite the opposite effect.

This is not to deny the existence of pogroms and ghettos, but only to assert that these horrors have had an effect on the nerves of people who did not experience them, that among the various side effects is the local hysteria of Jewish writers and intellectuals who cry out from confusion, which they call oppression and pain.

We submit that this is a most desirable effect of the law -- and one of its principal aims.

Since appeals to morality, to humanity, and to sanity have had such small effect, perhaps our last recourse is the deterrent example.

The effect of radiation is cumulative over the years -- and on to succeeding generations.

A recent study on radiation exposure by the AEC's division of biology and medicine stated: `` The question of the biological effect of ( radiation ) doses is not considered '' herein.

A 5-percent royalty is paid on any production during the period the contract is in effect ; ;

A significant effect discovered during the study is the existence of Prandtl numbers reaching values of more than unity in the nitrogen dissociation region.

Another effect discovered is the large coefficient of thermal diffusion tending to separate nitrogen from the oxygen when temperature differences straddling the nitrogen dissociation region are present.

The pre-1960 rate of Federal participation with respect to any State's base allotment, as well as the adjusted rate in effect during the 1960 - 1962 period, is designated by the statute as that State's `` adjusted Federal Share ''.