Optics: Fresnel diffraction - adjustable slit | MIT Video Demonstrations in Lasers and Optics

Optics: Fresnel diffraction - adjustable slit
Instructor: Shaoul Ezekiel
View the complete course: ocw.mit.edu/RES...
License: Creative Commons BY-NC-SA
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[@sadiqsaleem5883]

I think Fresnel did not used any type of lens in his experiment but Fraunhofer used two lenses to make the beam of light parrallel so that the distance between light source and the screen could be infinity. We get the fringes because of the constructive and destructive interference and can be observed by the help of Michelson interferometer. #Feedback_Please :)

[@VineetBhakhar]

Stunning!

[@hamdaniyusuf_dani]

I think the fringes in so called Fresnel diffraction here are actually interference pattern between direct light beam and specularly reflected light beam by the edges of the slit, just like the case of Lloyd's mirror.

[@volkerblock]

No!!!!!

[@hamdaniyusuf_dani]

@@volkerblock There's also light beams diffracted by each edges that contribute to the interference pattern.

[@vujean8670]

That was awesome

[@vrindaasokan9062]

Mr.Shaoul Ezekiel, why are we using a short focal length lens?

[@darranedmundson1505]

He wants a bright point source of illumination. Without the lens, almost all of the light wouldn’t hit the pinhole. The effect on the screen would still be there … but it would be so dim as to be invisible.

[@alfredli4032]

​@@darranedmundson1505 The primary reason use a lens here is considering the same observation distance, the Fresnel diffraction pattern has a significantly smaller size than Fraunhofer diffraction pattern which makes it very hard for clealy demonstration with a camera at that time. A short focal length lens is employed precisely to "unfold" the diffraction pattern on the screen. Additionally, placing the slit behind the pinhole ensures that the incident wave at the entrance surface of the slit still is a spherical wave. Imrovements of the brightness is just a side effect.

[@nazmulhasanshadhin2489]

Can I use a laser pointer of 650 nm wavelength to do the experiment??

[@volkerblock]

yes

[@volkerblock]

You can also carry out the experiments yourself at home with the simplest means (green laser pointer and simple slot). A Cornu-Sparale also shows where the dark stripe in the middle comes from. Unfortunately in German, I'm sorry, just turn off the sound.

[@volkerblock]

kzbin.info/www/bejne/nqWXfYaNlpaHo5o