# Light intensity profile along all radial distances

• XLAYZ
In summary: However, as the beam travels away from the antenna, the intensity decreases as the radial distance increases.
XLAYZ
Hello,

I have an ordinary light (not laser) collimated to produce a parallel beam. After traveling a distance in air, the beam has diverged significantly. The intensity decreases as the radial distance increases. Now I need to estimate the intensity profile along all radial distances inside the beam. All what I found was about laser beam and Gaussian beam, it is not the same thing. Could anyone please show me what theory and which formula I need to use?

Thank you in advance!

Once we are more than a certain distance from the source (the boundary of the Radiation Near Field), the intensity falls with the inverse square law. This applies along any radial.
The boundary of the radiation Near Field is quite indistinct, and for a collimated beam is sometimes given as the Rayleigh Distance = diameter of source^2 / 2 lambda.
The same applies to laser beams, radio beams and microwave beams, water waves etc.

When you say "radial" which radius do you mean? The radius ##R## of a sphere centered at the source or the radius ##r## of the circular spot of collimated light at distance ##R## from the source?

kuruman said:
When you say "radial" which radius do you mean? The radius ##R## of a sphere centered at the source or the radius ##r## of the circular spot of collimated light at distance ##R## from the source?
Sorry, I mean the radial distance from the axis of the beam with circular cross section.

Sorry, I had misunderstood the meaning of"radius". If the radiating aperture is circular and uniformly illuminated, we see a tapered central lobe, followed by a succession of nulls and gradually diminishing peaks, known as sidelobes. This is called an Airy pattern, named after the former Astronomer Royal. See Wiki, https://en.wikipedia.org/wiki/Side_lobe
Close to the antenna, within the radiation near zone, the beam is essentially parallel.

## 1. What is a light intensity profile along all radial distances?

A light intensity profile along all radial distances is a graphical representation of the intensity of light at different distances from a central point. It shows how the intensity of light changes as you move away from the source in all directions.

## 2. How is a light intensity profile along all radial distances measured?

A light intensity profile along all radial distances is typically measured using a light intensity meter or a spectrophotometer. These devices measure the amount of light at different distances from a source and create a graph of the results.

## 3. What factors can affect the shape of a light intensity profile along all radial distances?

The shape of a light intensity profile along all radial distances can be affected by several factors, including the type of light source, the distance from the source, and any obstructions or reflections in the environment.

## 4. How is a light intensity profile along all radial distances useful in research?

A light intensity profile along all radial distances is useful in research as it can provide information about the distribution of light from a source. This can be helpful in understanding how light interacts with different materials or how it affects living organisms.

## 5. Can a light intensity profile along all radial distances be used to compare different light sources?

Yes, a light intensity profile along all radial distances can be used to compare different light sources. By measuring and graphing the intensity of light from different sources at various distances, researchers can determine which source produces the most consistent or strongest light output.

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