Young double slit experiment

In summary, the interference pattern disappears when determining which slit a photon or atom has gone through, but this can be done without destroying the particle. In a smokey environment, the diffusion of particles can act as a detector volume to measure position, but this may not have a significant impact on the interference pattern. By using polarizers at perpendicular angles, the interference can be eliminated, but setting them at parallel angles preserves the interference pattern with lower contrast.
  • #1

Jip

20
2
Hi,
My question is the following:
As well known, the interference pattern disappears when one determines which slit the photon has gone through. This also holds for atoms and molecules. Now I understand how the actual experiment works for eg. an atom: They send excited atoms that can decay in some cavity coupled to a photomultiplier; this way one can be sure whether the atom has been through slit 1 or slit 2.

But how does the experiment work with photons? What does it mean here to determine which slit the photon has gone through? (in particular, without destroying the photon!)

Related to this: lasers can be seen by eye if they go through some smoke. What if the double slit experiment is realized in some smokey environment? Does the diffusion on the particles "measure" the photon position? If so, we should see on the screen some interference for photons that have not been measured + two peaks corresponding to photons that have been measured.
Is that correct? If so, does anyone have references to provide?

Many thanks!
 
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  • #2
You can use a polarizer - not all photons will go through, but if they do you know which slit they went through if you measure the polarization.

Jip said:
What if the double slit experiment is realized in some smokey environment? Does the diffusion on the particles "measure" the photon position?
Yes, but only the position of particles that get scattered, they won't make it through the slits anyway (if they get scattered before). Smoke behind the double-slits acts like a three-dimensional detector volume.
Well, a few photons might get scattered very close to a slit, but probably not enough to make a visible difference.
 
  • #3
Just to add to mfb's comment: Typically you would set the left polarizer at perhaps 0 degrees, and the right at 90 degrees. I.e. any angles where they are perpendicular. That eliminates the interference.

If you make them parallel (the same angles), there WILL be interference. In this manner, you can see that the interaction with the polarizer itself does NOT determine the interference. It is the relationship between them that controls.
 
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  • #4
Yep, and then you can set the left polarizer to 0 deg and the right one to any angle ##\alpha##. If ##\alpha \neq 90^{\circ}##, you only get uncertain which-way information but the interference pattern is preserved with lower contrast :-).
 

1. What is the Young double slit experiment?

The Young double slit experiment is a classic experiment in physics that demonstrates the wave-like nature of light. It involves a light source, two parallel slits, and a screen. When light passes through the slits, it diffracts and creates a pattern of light and dark bands on the screen, known as interference fringes.

2. How does the Young double slit experiment show the wave-like nature of light?

The interference fringes produced in the Young double slit experiment can only be explained by the wave theory of light. This is because the bright and dark bands are created by the constructive and destructive interference of light waves passing through the two slits. This phenomenon is not possible if light is considered as a particle.

3. What is the purpose of using two slits in the Young double slit experiment?

The two slits in the Young double slit experiment are used to create two coherent light sources. This means that the light waves passing through the two slits have a constant phase relationship with each other. This is necessary for the interference pattern to form on the screen. If only one slit is used, there will be no interference and the pattern will not be observed.

4. Can the Young double slit experiment be performed with other types of waves?

Yes, the Young double slit experiment can be performed with other types of waves, such as sound waves or water waves. In fact, Thomas Young originally performed this experiment using water waves. The interference pattern formed by these waves follows the same principles as that of light waves, demonstrating the wave-like nature of all types of waves.

5. What are the real-world applications of the Young double slit experiment?

The Young double slit experiment has many practical applications, particularly in the field of optics. It is used in the design of optical instruments, such as telescopes and microscopes, to reduce the effects of diffraction and improve image quality. It is also used in the development of optical coatings for lenses and mirrors, as well as in the study of diffraction of light through various materials.

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