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

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.

This is a subjective speckle pattern.

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

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.

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.

If the position of the imaging system is altered, the pattern will gradually change and will eventually be unrelated to the original speckle pattern.

A photograph of an objective speckle pattern.

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

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.

The speckle pattern in the figure was obtained by pointing a laser beam at the surface of a mobile phone so that the scattered light fell onto an adjacent wall.

A photograph was then taken of the speckle pattern formed on the wall ( strictly speaking, this also has a second subjective speckle pattern but its dimensions are much smaller than the objective pattern so it is not seen in the image )

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.

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

The change in speckle size with lens aperture can be observed by looking at a laser spot on a wall directly, and then through a very small hole.

When the speckle pattern changes in time, due to changes in the illuminated surface, the phenomenon is known as dynamic speckle, and it can be used to measure activity, as in ( for example ) an optical computer mouse.

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

A more detailed discussion on laser speckle reduction can be found in

In scientific applications, a spatial filter can be used to reduce speckle.

Other methods can achieve resolving power exceeding the limit imposed by atmospheric seeing, such as speckle imaging, aperture synthesis, lucky imaging, and space telescopes, such as the Hubble Space Telescope.

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.

Resolution limits can also be overcome by adaptive optics, speckle imaging or lucky imaging for ground-based telescopes.

# 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 )

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.

All of these were obtained using speckle imaging and have higher resolution than can be obtained with e. g. the Hubble Space Telescope:

In the aperture masking technique, the bispectral analysis ( speckle masking ) method is typically applied to data taken through masked apertures, where most of the aperture is blocked off and light can only pass through a series of small holes ( subapertures ).

Although the signal-to-noise of speckle masking observations at high light level can be improved with aperture masks, the faintest limiting magnitude cannot be significantly improved for photon-noise limited detectors ( see Buscher & Haniff ( 1993 )).

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

Spatial coherence of laser beams also manifests itself as speckle patterns and diffraction fringes seen at the edges of shadow.

Speckle imaging ( also known as video astronomy ) describes a range of high-resolution astronomical imaging techniques based either on the shift-and-add (" image stacking ") method or on speckle interferometry methods.

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.

The technique, also known as dynamic speckle enables real-time monitoring of dynamical systems and video image analysis to understand biological processes.

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.

Lucky imaging ( also called lucky exposures ) is one form of speckle imaging used for astronomical photography.

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.

In 1976, component A was itself discovered to be a binary star, using speckle interferometry and the 2. 1-meter telescope at the Kitt Peak National Observatory.

In 1970 the French astronomer Antoine Labeyrie showed that information could be obtained about the high-resolution structure of the object from the speckle patterns using Fourier analysis ( speckle interferometry ).

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