How to observe Fresnel diffraction at home?

[jinawee]

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.

 

[ppoonamk]

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.