Diffraction refers to the deflection of waves at an obstacle. This obstacle can be a single slit, a double slit, or a multiple slit. This article explains everything about diffraction at a single slit. The topic is part of the theory of waves and belongs to the subject of physics.
What is diffraction?
In general, diffraction is the deflection of waves by an obstacle. Diffraction is also sometimes referred to as diffraction. Diffraction of rectilinear propagation of waves occurs when a wave hits an obstacle or goes through a gap. These waves can be sound waves, light waves or water waves, among others. Diffraction can also be explained using Huygens’ principle.
Diffraction occurs when there is an obstacle in the way of a wave. Only part of the wave front then gets past the obstacle and part does not. Using Huygens’ principle, it is possible to determine the light distribution behind the obstacle.
The interference (link) has already been explained in another article. The terms interference and diffraction are quite similar as they basically describe the same phenomenon. Therefore, it is important to know the distinction. One speaks of diffraction when only a single slit is considered. When several columns interact, we speak of interference.
- Diffraction is the deflection of waves at an obstacle. This can be a single slit, double slit or multiple slit.
- Diffraction is described according to Huygens’ principle.
- Unlike interference, when light diffracts, you only look at a single slit.
The Huygensian principle
The Huygens principle is a principle after Christiaan Huygens and can also be called the Huygens-Fresnel principle. It states that every point of a wave front can be considered as the starting point of a new wave. One also speaks of the elementary wave. The new position of the wavefront results from the superimposition of all elementary waves, also known as superposition.
Huygens’ principle says that the light wave continues past an obstacle as if a new elementary wave were emanating from each point of the opening. These waves propagate in the same medium and at the same speed as the original wave.
Source: www.wikipedia.de
- Huygens’ principle states that every point on a wave front can be regarded as the starting point of a new wave.
The diffraction of light at a single slit
As mentioned above, diffraction of light occurs when light hits an obstacle. These obstacles can be single slit, double slit, or multiple slit, also known as grating. In this article we deal with the diffraction of light at a single slit.
Light diffraction occurs when a light wave hits a single slit. Diffraction occurs at this slit and a new wave front is formed behind the slit according to Huygens’ principle. These elementary waves propagate uniformly in all directions behind the slit and are superimposed.
They form an interference pattern. This is caused by constructive and destructive interference of the elementary waves. The article on interference explains destructive and constructive interference. Just click on the term and you will get to the article.
In some places minima can be observed where no light arrives. The elementary waves interfere destructively here. At other locations, maxima can be observed where the elementary waves interfere constructively.
The minimums
Minima are the points on the screen where no light arrives. That means there is a minimum when all elementary waves interfere destructively. This occurs when the path difference Δs between the upper and lower marginal ray is equal to a multiple of the wavelength. You can find out what the path difference is in the article on phase shift and path difference. Therefore, for the minima:
Δs=k⋅λ
Δs stands for the path difference and λ for the wavelength of the incident wave. k stands for a multiple.
The maxima
Maxima are the points on the screen between the minima where the most light arrives. A maximum occurs when only a few waves interfere destructively. This occurs when the path difference Δs between the upper and lower marginal ray is equal to a multiple of the wavelength plus half a wavelength. Therefore, for the maxima:
Δs=k⋅λ+0.5⋅λ= ⋅λ
The figure below shows how the diffraction of light at a single slit can be illustrated by a diagram.
Source: www.mikrokristalle.com
- Light diffraction occurs when a light wave hits a single slit. After the gap, a new wave front is formed, which spreads out evenly in all directions and is superimposed.
- An interference pattern results from constructive and destructive interference of the waves.
- Minima are places where no light arrives. The elementary waves interfere destructively. The following applies: Δs=k⋅λ
- Maxima are points where the most light arrives. The elementary waves interfere constructively. The following applies: Δs= ⋅λ
The angle α
A connection can now also be established between the angle α and the positions of the minima or maxima. The intended angle is shown in the diagram below. It can be calculated by the formula: sinα=Δs/d
d stands for the size of the gap, i.e. the gap width.
This formula can now be applied to maxima and minima, respectively, by replacing Δs with the respective formulas for maxima and minima that have already appeared earlier in the article.
The following then results for the minima: sinα=(k⋅λ)/d
The maxima are: sinα=(0.5⋅λ+k⋅λ)/d =⋅λ
What applies to the diffraction of light at a single slit?
The following applies to the diffraction of light at a single slit:
- The smaller the slit that the light goes through, the more the light bends around that slit.
- The intensity of the light decreases as the angle increases.
- As a rule, the gap is larger than the wavelength of the incident light. There is therefore a whole wavefront, since a new elementary wave emanates from every point in the slit.
Diffraction at a single slit – everything important at a glance
- Diffraction is the deflection of waves at an obstacle. This can be a single slit, double slit or multiple slit.
- Diffraction is described according to Huygens’ principle.
- Huygens’ principle states that every point on a wave front can be regarded as the starting point of a new wave.
- Light diffraction occurs when a light wave hits a single slit. After the gap, a new wave front is formed, which spreads out evenly in all directions and is superimposed.
- An interference pattern results from constructive and destructive interference of the waves.
- Minima are places where no light arrives. The elementary waves interfere destructively. The following applies: Δs=k⋅λ
- Maxima are points where the most light arrives. The elementary waves interfere constructively. The following applies: Δs= ⋅λ
- The relationship between the angle and the positions of maxima and minima can be described as follows: sinα=Δs/d