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Offline hamdani yusuf

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Investigation on diffraction of light
« on: 29/03/2016 07:32:37 »
In this topic I'd like to share my investigation on diffraction of light. In the first video I talk about definition and misconceptions that are often made.
I'd like to hear your opinion on this issue.


 

Offline hamdani yusuf

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Re: Investigation on diffraction of light
« Reply #1 on: 29/03/2016 14:27:12 »
Let me summarize my experiments in investigating diffraction of light.
Video #1 : Definition and misconceptions. Here I talk about sources of confusions we often find when discussing diffraction of light. The experiment shows the simplest case of light diffraction, which is diffraction by single edge obstruction. Basically diffraction is a name given to the phenomenon where light (or electromagnetic wave in general) can reach region behind an obstacle. It can occur when the edge of the obstacle intersect with the light beam.
Video #2 : Edge shapes effect. It shows various diffraction patterns produced by different shapes of obstacles. Here we use sharp and blunt edges, which are considered as cylindrical, and spherical obstacle.
Video #3 : Diffraction by transparent objects. It shows that transparent objects like plastic sheet can also produce diffraction. Even when the obstacle has a very similar refractive index compared to the medium, which makes it almost invisible. Here I used borosilicate glass that is immersed in sunflower oil.
Video #4 : Non-diffractive Obstacle. It shows a case where the edge of an obstacle can block a light beam without producing diffraction pattern. Here the interface between the glass and the air acts as total internal reflector which prevent the light from reaching the area behind the reflector.
 

Offline hamdani yusuf

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Re: Investigation on diffraction of light
« Reply #2 on: 29/03/2016 14:59:27 »
The next videos demonstrate the effect of diffraction by obstacles with more than 1 edges.
Video #5 : Double edged Obstacle. It shows the effect of diffraction produced by obstacles with 2 edges exposed to the light beam. This can be divided into 2 types : outer and inner obstacle. Outer type trims the light beam from the outer sides, and usually referred as single slit diffraction. The inner type is often called thin wire diffraction. They produce similar pattern of light and dark bands as a result of constructive and destructive interference of light from the edges.
Video #6 : Triple edged Obstacle. It shows the effect of diffraction and interference produced by adding one more edge to the obstacle. It's interesting that this experiment is never even mentioned in mainstream physics text books.
Video #7 : Quadruple edged Obstacle. The famous double slit interference is basically an outer type of quadruple edged obstacle. Its complementary inner type is the double wire obstacle, but this is very rarely discussed in physics class room.
Video #8 : Multiple edged Obstacle. Here more edges are added to the obstacles. It also shows experiment using diffraction gratings which most of us are familiar with.
 

Offline hamdani yusuf

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Re: Investigation on diffraction of light
« Reply #3 on: 29/03/2016 15:18:04 »
In the next videos, I show the diffraction pattern where the light source comes from various angle.
Video #9 : Horizontally tilted aperture. Here we show the effect of tilting the diffraction aperture horizontally. There is also a case of single slit diffraction with large horizontally tilted angle where the gap is actually very large compared to the wavelength. Nevertheless we can still see interference pattern.
Video #10: This video shows the effect of vertically tilting the obstacle on a light beam. The pattern seems to follow a specular reflection by cylindrical objects, which is unexplainable using Huygens’s principle.
Video #11: Diffraction of non-parallel Light Source. It's repeating experiments on diffraction of light, but now using non-parallel light source by passing the laser beam through lenses.
 

Offline hamdani yusuf

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Re: Investigation on diffraction of light
« Reply #4 on: 29/03/2016 15:28:10 »
Finally the last videos of this series.
Video #12: Non-diffractive Interference. There are some other optical phenomena which create interference pattern but don’t actually involve diffraction. Some sources use the term diffraction to mention some of these interference cases as if those terms are interchangeable. The video lists them up to make distinction between diffraction and interference of light clearer. 
Video #13: Non-diffractive slit. Here we put Huygen’s principle as currently accepted explanation for single slit diffraction to the test. To determine whether the space or the edges of the slit as the real interfering point sources, we can conduct an experiment using a slit whose edges are not diffractive. If Huygen’s principle is correct, then we should still get interference pattern even though the edges of the slit doesn’t diffract light.
 

Offline alancalverd

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Re: Investigation on diffraction of light
« Reply #5 on: 30/03/2016 20:06:50 »
First video is excellent! Looking forward to the rest!
 

Offline hamdani yusuf

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Re: Investigation on diffraction of light
« Reply #6 on: 31/03/2016 02:29:46 »
Here is Youtube complete playlist of these experiments.
/playlist?list=PLZ2PyRUoub7hmjVJT1gs03DzoVW32kLn7
 

Offline hamdani yusuf

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Re: Investigation on diffraction of light
« Reply #7 on: 31/03/2016 09:39:50 »
The rest of the video can be watched here
video #2
video #3
video #4
« Last Edit: 31/03/2016 16:10:14 by hamdani yusuf »
 

Offline hamdani yusuf

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Re: Investigation on diffraction of light
« Reply #8 on: 31/03/2016 16:15:48 »
video #5
video #6
video #7
video #8
 

Offline hamdani yusuf

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Re: Investigation on diffraction of light
« Reply #9 on: 31/03/2016 16:17:52 »
video #9
video #10
video #11
video #12
video #13
 

Offline hamdani yusuf

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Re: Investigation on diffraction of light
« Reply #10 on: 29/06/2016 02:29:46 »
Does someone have access to Vantablack? Its usage is currently restricted for public use.
I'd like to see if single edge diffraction can still occur when the obstacle absorb more than 99.9% of the light hitting its surface.
I also want to see double edge diffraction, or widely known as single slit diffraction with aperture covered by Vantablack.
 

Offline hamdani yusuf

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Re: Investigation on diffraction of light
« Reply #11 on: 21/11/2016 15:22:04 »
I've added a new video regarding non-diffractive object whose shape resembles normal objects, unlike the one shown in video#4. The similarity is that both use total internal reflection.
youtube.com/watch?v=NULSN3OZAlQ
 

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Re: Investigation on diffraction of light
« Reply #11 on: 21/11/2016 15:22:04 »

 

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