# Please, can someone explain me spatial coherence?

• azatkgz
In summary, spatial coherence refers to the spatial extent over which all frequency components of a wave are in phase with each other. It is related to the size of a source and can be measured using a Young's double-slit interferometer. The van-Cittert-Zernike theorem states that the far-field diffraction pattern of a beam is proportional to the spatial coherence. Longitudinal coherence, which refers to the waveband, can cause the far-field diffraction pattern to appear smoother when passing through a pinhole.

#### azatkgz

Please,can someone explain me spatial coherence?

Spatial coherence is the spatial extent over which all the frequency components of a wave are in phase (or close to it) with each other.

As waves propagate they tend to lose their spatial coherence due to the phases of different frequency components drifting apart.

Claude.

Spatial coherence is related to the size of a source, and means how well you can predict the field values *over there*, if I know what it is *here*. A point source produces a perfectly spatially coherent wavefront, while an infitely large source is perfectly spatially incoherent.

The van-Cittert-Zernike theorem is a very profound statement and worth spending time to understand. Briefly, the far-field diffraction pattern of a beam is proportional to the spatial coherence.

Spatial coherence is typically measured by a Younng's double-slit interfereometer, where the slit spacing is a measure of the spatial coherence.

Spatial coherence is the reason the holograms on credit cards look good outside in the sun, and terrible inside under fluorescent lights.

what does the SHORT longtudinal coherence do to its far-field diffraction when it passes through a pinhole? Thanks.

Andy Resnick said:
Spatial coherence is related to the size of a source, and means how well you can predict the field values *over there*, if I know what it is *here*. A point source produces a perfectly spatially coherent wavefront, while an infitely large source is perfectly spatially incoherent.

The van-Cittert-Zernike theorem is a very profound statement and worth spending time to understand. Briefly, the far-field diffraction pattern of a beam is proportional to the spatial coherence.

Spatial coherence is typically measured by a Younng's double-slit interfereometer, where the slit spacing is a measure of the spatial coherence.

Spatial coherence is the reason the holograms on credit cards look good outside in the sun, and terrible inside under fluorescent lights.

As I mentioned privately, since 'longitudinal' coherence refers to the waveband, the far-field diffraction pattern will appear smoothened out: each color will give a (for example) Airy pattern, but if there is a broad spectrum of colors, the total pattern will appear as a smooth blob.

## 1. What is spatial coherence?

Spatial coherence refers to the degree to which different parts of a wave or signal are in phase with each other. In simpler terms, it describes how well the different parts of a wave or signal are aligned with each other.

## 2. Why is spatial coherence important?

Spatial coherence is important because it is a key factor in determining the quality of imaging and sensing systems. It also affects the behavior of light and other electromagnetic waves, making it crucial in fields such as optics and telecommunications.

## 3. How is spatial coherence measured?

Spatial coherence is typically measured using interference patterns, which are created when two or more coherent waves interact with each other. These patterns can be analyzed to determine the level of coherence between the waves.

## 4. What factors affect spatial coherence?

The main factors that affect spatial coherence are the distance between the sources of the wave or signal, the wavelength of the wave, and any disturbances or obstructions in the path of the wave.

## 5. How is spatial coherence used in real-world applications?

Spatial coherence has many practical applications, such as in holography, imaging techniques like optical coherence tomography, and in the design of high-speed communication systems. It is also important in fields such as astronomy, where it helps in the analysis of astronomical images and signals.