[hamdani yusuf (OP)]

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.

[hamdani yusuf (OP)]

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.

[hamdani yusuf (OP)]

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.

[hamdani yusuf (OP)]

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.

[hamdani yusuf (OP)]

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.

[alancalverd]

First video is excellent! Looking forward to the rest!

[hamdani yusuf (OP)]

Here is Youtube complete playlist of these experiments.
/playlist?list=PLZ2PyRUoub7hmjVJT1gs03DzoVW32kLn7

[hamdani yusuf (OP)]

The rest of the video can be watched here

video #2 Edge shapes effect

video #3 Diffraction by transparent objects

video #4 Non-diffractive Obstacle

[hamdani yusuf (OP)]

video #5 Double edged Obstacle

video #6 Triple edged Obstacle

video #7 Quadruple edged Obstacle

video #8 Multiple edged Obstacle.

[hamdani yusuf (OP)]

video #9 Horizontally tilted diffraction

video #10 Vertically tilted diffraction

video #11 Non-parallel light source

video #12 Non-diffractive interference

video #13 Non-diffractive slit

[hamdani yusuf (OP)]

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.

[hamdani yusuf (OP)]

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

[hamdani yusuf (OP)]

After a long break, I finally finish a new video demonstrating that geometrical optics is still working in the formation of diffraction patterns.

[WarnerGet]

Im a second year high school and I need a science investigatory project about making something out of something. Like recycling something to make something that can be of use in the environment. I need it now. As in this time. Please........... Thanks.

[hamdani yusuf (OP)]

In the video on vertically tilted diffraction, the clip is unexpectedly cut when showing the pattern from optic fiber. Here is the raw take of the experiment.

[hamdani yusuf (OP)]

Here's my newest video investigating diffraction of light by producing single side interference pattern.

[hamdani yusuf (OP)]

Here's one of the most helpful pictures to understand the phenomenon of diffraction and interference of light.

Same double-slit assembly (0.7 mm between slits); in top image, one slit is closed. In the single-slit image, a diffraction pattern (the faint spots on either side of the main band) forms due to the nonzero width of the slit. This diffraction pattern is also seen in the double-slit image, but with many smaller interference fringes.

In this case, the slits are narrower than the opaque matter between them.

In my next video, I'll show the result of double wire experiment, which is the equivalent of double slit experiment, according to Babinet's principle.

We'll see the pattern produced by thin wires with narrow and wide gap between them. The pictures above are similar to the pattern produced by single thin wire, and double wire with wide gap, respectively.

We'll also see pattern produced by thick wires (I actually used needles) with narrow gap between them. The result turns out to be similar to the bottom picture above. But if one needle is removed, what we get is a pattern of narrow fringes where the central bright is twice as wide as the others.

[Bored chemist]

I once made a diffraction grating using wires (separated by the threads of two bolts)
It didn't work properly until I painted it black.
The reflections from the curved surfaces of the wires made the diffraction pattern more complicated.

You may encounter similar issues with needles.

[hamdani yusuf (OP)]

I once made a diffraction grating using wires (separated by the threads of two bolts)
It didn't work properly until I painted it black.
The reflections from the curved surfaces of the wires made the diffraction pattern more complicated.

You may encounter similar issues with needles.

Here are my results of double wire diffraction experiment. The first picture is the direct laser spot when allowed to hit the wall without obstruction. Due to lens imperfection, some artefact is visible on the wall. To avoid complication, the laser is oriented so that the spots are aligned vertically, which is on the same axis as the obstructing needles that will be used.


Below is the pattern produced by single needle.


And the pattern produced by double needle.


Notice the width of the central bright fringe, compared to other fringes. In single needle, its approximately twice as wide. Whereas in double needle, it has the same width. It's similar to single slit and double slit experiment, respectively. Moreover, the double needle creates more prominent dark fringes compared to single needle.

[hamdani yusuf (OP)]

Finally finished the video demonstrating single and double thin wire diffraction-interference experiment.