# Why in Huygens–Fresnel, Point source should be as small as wavelength?

• payam
In summary, the Huygens-Fresnel principle states that for diffraction pattern configuration, each point on the aperture must be considered as a point source of light. When creating a simulation for diffraction, it is important to use a size for each point source that is comparable to or smaller than the wavelength being used. This ensures accurate results and a reasonable simulation runtime. The definition of a point source is a source significantly smaller than the wavelength, but in some simulations, extended sources can be used as long as their sizes are comparable to the wavelength.
payam
In Huygens–Fresnel principle, to configure the diffraction pattern after an aperture, we need to consider each point on aperture as a point source of light.
I need to make a simulation for diffraction. Here I will need to introduce the size of each point source.
my question is why the size of these point sources should be as large as the used wavelength ?

Because if they were any larger they would be extended sources - not point sources - affecting the results, and if they were smaller your simulation would take longer than necessary to run. I would use a size a bit smaller to be on the safe side. A quarter wavelength seems appropriate.

Thanks Dauto.
So there is a definition for point source in terms of angular divergence?
what is the definition of a point source?

payam said:
Thanks Dauto.
So there is a definition for point source in terms of angular divergence?
what is the definition of a point source?

A point source is a source significantly smaller than the wavelength of the radiation being emitted. Otherwise it is an extended source.

payam said:
Here I will need to introduce the size of each point source.

By definition, a point has zero size, doesn't it?

jtbell said:
By definition, a point has zero size, doesn't it?

Yes, it does, but (s)he is talking about some kind of simulation. It's not exactly clear how the simulation works but it is conceivable that an infinite number of point sources could be replaced with a finite number of extended sources and as long as the sizes are comparable to the wavelength or smaller the simulation might produce viable results. Again, not knowing exactly how the simulation is supposed to work, I'm going out on a limb trying to make sense of it. May be the OP should explain the simulation better?

## 1. Why is the point source important in Huygens-Fresnel principle?

The Huygens-Fresnel principle states that every point on a wavefront acts as a source of secondary spherical waves. This means that all the points on a wavefront are equally important in determining the direction of propagation of the wave. Therefore, the point source is crucial in this principle as it allows us to analyze complex wave phenomena by breaking them down into simpler spherical waves.

## 2. How does the size of the point source affect the Huygens-Fresnel principle?

The size of the point source directly affects the accuracy of the Huygens-Fresnel principle. If the point source is smaller than the wavelength of the wave, the secondary spherical waves will be more precise and the principle will hold true. However, if the point source is larger than the wavelength, the secondary waves will be distorted and the principle will not accurately describe the wave behavior.

## 3. Why is it important for the point source to be as small as the wavelength?

When the point source is as small as the wavelength, the secondary spherical waves will be able to accurately represent the original wavefront. This allows for a more accurate analysis of wave phenomena and helps us to understand complex wave behavior. It also allows for the Huygens-Fresnel principle to be applied in a wide range of situations.

## 4. Can the point source ever be smaller than the wavelength?

No, the point source cannot be smaller than the wavelength as it is a theoretical concept used in the Huygens-Fresnel principle. In reality, a point source cannot exist as it would have an infinite intensity. However, for practical purposes, the point source is considered to be smaller than the wavelength when the size of the source is significantly smaller than the wavelength.

## 5. How does the Huygens-Fresnel principle apply to different types of waves?

The Huygens-Fresnel principle can be applied to a wide range of wave phenomena, including electromagnetic waves, acoustic waves, and water waves. This is because it is a fundamental principle that describes the behavior of any type of wave, regardless of its nature. However, the specific equations and calculations may vary depending on the type of wave being analyzed.

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