How to observe Fresnel diffraction at home?

In summary, the conversation revolved around using a homemade setup to observe the difference between Fraunhofer and Fresnel diffraction. The main components mentioned were a He-Ne laser, a short-focal lens, a pinhole, and an adjustable aperture. There were also questions about alternative materials, the type of lens needed, and the recommended size for the pinhole. It was suggested that the same effects could be observed with a sharp razor blade and that a positive lens would be needed to convert the laser beam into a converging cone of light. Diffraction at the exit pupil would cause Fresnel rings near the focus.
  • #1
jinawee
28
2
I would like to see the difference between Fraunhofer and Fresnel diffraction with a homemade setup. Has anyone achieved this?



In this example, it seems that the main components are a He-Ne laser, a short-focal lens, a pinhole and an adjustable aperture.

I have some doubts about the possible alternative materials. Would a common laser pointer have the same effect? What lens should I need? What pinhole do you recommend? I've seen that the optimum size is around 0.1-1 mm.

Thanks.
 
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  • #2
You could observe the same effects at the edge of a sharp razor blade.
You will need a positive lens to covert your laser beam into a converging cone of light that passes through the exit pupil. Diffraction at the exit pupil
causes Fresnel rings near the focus, which get smaller as the camera approaches the focus.
 

Related to How to observe Fresnel diffraction at home?

1. How can I create a diffraction pattern at home?

To create a diffraction pattern at home, you will need a small point light source, such as a laser pointer or a small LED flashlight. Place the light source in a dark room and shine it through a small slit or opening onto a screen. This will create a diffraction pattern on the screen that you can observe.

2. What is the difference between Fresnel and Fraunhofer diffraction?

The main difference between Fresnel and Fraunhofer diffraction is the distance between the source of light and the screen where the diffraction pattern is observed. In Fresnel diffraction, the distance is small and the pattern is observed close to the light source, while in Fraunhofer diffraction, the distance is large and the pattern is observed far from the light source.

3. Can I use a regular flashlight for Fresnel diffraction?

No, a regular flashlight will not work for Fresnel diffraction because the light emitted is not a point source. To observe Fresnel diffraction, you need a point light source that emits coherent light, such as a laser pointer or an LED flashlight.

4. How does the size of the slit affect the diffraction pattern?

The size of the slit has a significant impact on the diffraction pattern. A wider slit will produce a wider central maximum and smaller diffraction fringes, while a narrower slit will produce a narrower central maximum and larger diffraction fringes. The width of the slit also affects the intensity of the diffraction pattern.

5. Is it possible to observe Fresnel diffraction without a screen?

Yes, it is possible to observe Fresnel diffraction without a screen by using a diffraction grating. A diffraction grating is a surface with many fine, evenly spaced lines that act as multiple slits and produce a diffraction pattern when light is shone on it. This pattern can be observed without the need for a screen.

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