How to interpret the diffraction envelope

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In summary, interpreting the diffraction envelope involves analyzing the pattern of diffracted light, which is formed when a beam of light passes through a narrow slit or aperture. The envelope represents the intensity of the diffracted light at different angles, and its shape can provide information about the size and shape of the diffracting object. By understanding the principles of diffraction and analyzing the diffraction envelope, scientists and researchers are able to gain insights into the properties of materials and particles that are too small to be observed directly.
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Bill Sellers
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Explanations of 2-slit interference sometimes show the interference pattern compared to a 1-slit diffraction pattern, and state that the latter represents a limit or envelope for the former. Is it correct to interpret the patterns as representing (directly or indirectly) the number of photons being detected at locations on the screen? If so, then wouldn’t this imply that fewer photons are detected in the 2-slit setup vs. 1-slit?
 
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Bill Sellers said:
If so, then wouldn’t this imply that fewer photons are detected in the 2-slit setup vs. 1-slit?
When you compare number of photons to the screen between a single slit and a double slit experiment, you need to specify what is the same and what is different. Of course the source intensity is the same but what about the slit width? If the same number of photons per unit time goes through the double slit arrangement as goes through the single slit, then you should collect the same number of photons at the screen.
 
  • #3
Thank you very much for taking the time to respond to my query. I'm trying to understand a graphic such as the one at http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/dslit.html. I'm guessing that the single slit envelope shows the pattern you'd get if you closed one of the slits and doubled the width of the remaining one. If that guess is correct, then presumably the same number of photons per unit time should be going through. But the interference pattern doesn't seem to reflect that--it seems to be showing fewer photons.
 
  • #4
Such graphs are usually normalized to the peak intensity, so the absolute values of the count rates are not comparable.

As a rule of thumb: If you have one slit of a certain width which is illuminated with a certain intensity and now change to a different setting with two slits close to each other, where each of the two slits gets the same intensity as the single slit and has the same size, you will have twice the field in the area of constructive interference (if it is located in the middle between the slits). Accordingly, the peak intensity will be 4 times as high as before. If you use 3 slits, it will be 9 times as high. If you use many slits...you have just built a diffraction grating.
 
  • #5
4 times--thanks, that makes sense!
 

1. What is a diffraction envelope?

A diffraction envelope is a pattern of light or other electromagnetic radiation that is produced when a wave passes through a small opening or around an obstacle. It is characterized by a series of peaks and valleys that can be used to analyze the properties of the wave.

2. How is the diffraction envelope created?

The diffraction envelope is created when a wave, such as light, passes through a small opening or around an obstacle that is a similar size to its wavelength. This causes the wave to bend and interfere with itself, creating the characteristic pattern.

3. How do you interpret the diffraction envelope?

To interpret the diffraction envelope, you must analyze the peaks and valleys in the pattern. The location and spacing of these features can provide information about the size and shape of the opening or obstacle, as well as the wavelength of the wave.

4. What factors can affect the diffraction envelope?

The diffraction envelope can be affected by a variety of factors, including the size and shape of the opening or obstacle, the wavelength of the wave, and the distance between the wave source and the diffraction medium. Additionally, the properties of the medium, such as its refractive index, can also play a role.

5. How is the diffraction envelope used in scientific research?

The diffraction envelope is used in a variety of scientific fields, such as optics, acoustics, and X-ray crystallography. It can be used to study the properties of waves and the physical characteristics of materials, as well as to develop new technologies and techniques for analyzing and manipulating waves.

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