Diffraction: Classical Wave Behaviors

Collection of all the links I used to understand the subject — Collection Episode #00

Published in

Jungletronics

9 min readJun 12, 2022

Hi, on this page I will try to guide you through the fundamentals behind light.

We will use an awesome simulator here, too! Be tuned!

If you are in a hurry, see this vid: Diffraction (Young’s Double Slit & Grating) — A-level & GCSE Physics by Science Shorts.

Or this one: The Original Double Slit Experiment by Veritasium.

Or this simulator PhET sim from PhET — University of Colorado Boulder.

Or this one: ck-12 — Exploration Series — Physics Simulations from interactives.ck12.org (please, create your account, it is amazing! I highly recommend you create and enjoy all science they offer for free :).

Light is a particle or a wave?

Photo 1: A beach brings back good memories, doesn’t it? look at those beautiful waves…swimming there would be surreal! link

Diffraction is the generic name given to phenomena associated with deviations of light propagation predicted by geometric optics (i.e. Rectilinear Propagation of Light) and which reveal the light’s nature wave instead of a corpuscular matter.

Diffraction phenomena are observed for all types of waves. Rarely do we observe the diffraction of light in everyday life. Nonetheless, the diffraction of sound waves is difficult to avoid; the sound bypasses relatively large obstacles, such as people, trees, and furniture in a living room. This difference between the diffraction of sound and light is due to the difference between the respective lengths of waves. The wavelength of sound is of the order 1 m, while that of visible light is of the order of 500 nm.

For centuries scientists have debated over this issue. The wave-particle duality.

The Dutch physicist Christiaan Huygens (1629–1695) was one of the first to systematize the wave theory of light, in opposition to their contemporary Englishman Isaac Newton (1642–1727), who attributed the defense of a theory purely corpuscular.

The corpuscular theory of light, based on the Greek idea of atomism of antiquity, describes that light is composed of discrete particles called “corpuscles”, which describe a trajectory in a straight line, with limited speed.

The wave theory states that light is a wave, just as sound propagation. This wave model was based on the famous Experiment by Thomas Young (1773–1829), known as The Double Slit Setup, carried out in 1801, which involved the phenomena of diffraction and interference of light, the object of this study.

Welcome o/

Let’s get started!

Think about the harbor wall. If you have a harbor wall and waves are coming in, like here:

Photo 2: Look that wavelength is almost identical to the aperture. Diffraction is related to the wavelength, that’s for sure! Image From Diffraction — wave spreading around an edge by **Physics and Chemistry for IG and A level**

The walls are going to stop a lot of the wavefronts but when they go through the aperture the waves don’t just carry on as little waves here but no they’re going to spread out like that Photo 2. That’s what we call diffraction when waves go through a gap or around an object they diffract and fill in the empty space where the waves aren’t. This is incredible \o/

Hint: See these vids series from OpenLearn from The Open University: Properties of Waves — Exploring Wave Motion (1/5)

Wave Properties

Amplitude → Human perception of amplitude = loudness or volume;

Wavelength → 𝝀 { \lambda };

Frequency → Human perception of frequency = pitch (compasso in Portuguese, I guess…) or vibration.

What is volume and pitch?

Volume is a measure of how loud or soft something sounds and is related to the strength of the vibrations (amplitude-related). Pitch is a measure of how high or low something sounds and is related to the speed of the vibrations that produce the sound (frequency related). The sound is caused by vibrations (back and forth-movements).

Fundamental Equation 4 Wave Propagations

Fig. 3: Fundamental equation; please see this link

Photo 2: A beautiful basin formed by the math of waves :) link

google harbour wall waves diffraction and you’ll see a lot of mind-boggling examples; try it now!

This diffraction is related to the wavelength. Look…

Fig. 4: Diffraction Aperture dependence.

As you can see narrow gap tends to diffract more, right?

Sounds diffract like a wave. That’s awesome!

Remember that the diffraction is related to the wavelength (Photo 2). When the dimensions of the aperture have the same proportions as the width (amplitude) of the wave, then we can perceive this phenomenon. In our daily lives, we do not have this privilege, as the dimensions of obstacles are much larger than the dimensions of light waves. Look, just about the light, not about sound, that diffracts easily (Fig. 1).

Thomas Young — Double Slit setup (1801) states that this is the behavior of light. This explains why the man behind the wall can hear his pursuer’s footsteps on the dark side of the hall (Fig. 1).

Fig. 5: The Thomas Young Double Slit Experiment (1801). Indeed, a lot could be achieved with few resources…https://youtu.be/Iuv6hY6zsd0

Monochromatic light means one wavelength, constant phase difference. Laser nowadays is used instead of candles, and this is how we get the same effect generally we use red light and reddish light.

If the path difference is half a wavelength what does that mean that the waves arrived pi radians or 180 degrees out of phase they don’t constructively interfere they destructively interfere; they cancel each other out and we end up with a dark spot.

There is a constructive interference because the rays arrive in phase; if the path difference however is a multiple and a half of the wavelength then that means that the waves are going to arrive out of phase pi radians 180 degrees out of phase so that means that you end up destructive interference so that’s when you get a dark fringe. That’s the pattern you see in Fig. 5 above (fringes).

Constructive interference you end up with a bright fringe; dark fringes are because of destructive interference.

Fig. 7: The Single Slit Diffraction patterns

Diffraction from a single slit results that the interference central maximum being very intense, very bright compared to the other fringes, and also it is double the width of the fringes too (Fig. 7).

Fig. 8: The Double Slit Diffraction patterns; see that the formula is different from the previous one…

Now about the Young Double Slit setup observe that the central waves are much thinner and the fringes are much closer together (Fig. 8).

Diffraction grating (not shown here) is different from Young’s double slit instead of just having two slits like that instead we got lots and lots of slits that are very very small and we get lots and lots of diffraction happening when light passes through that and deflect afterward diffract as it goes through this is where we can’t use.

Virtual Simulator — Algetec — Brazil

From now on we will use the Algetec Simulator, which is a virtual laboratory that simulates the real environment and allows the student to carry out experiments without leaving home. Replicas with a high degree of fidelity to the traditional physical laboratory.

Fig. 9: Red Laser Experiment — Overview of the Virtual Laboratory Simulator of Algetec — ALGETEC has
enhanced the experience of students worldwide in their virtual labs in an extraordinary way. It’s a company
Brazilian company based in Porto Alegre — RS — Brazil. learning is guaranteed!

For all experiments, we will follow the following Virtual lab procedures:

1 — Turn on the laser;

Fig. 10: Turning the Laser On & Off — Place the cursor over the laser and click with the left mouse button. Switch state every click.

2 — Choose the emitter light wavelength:

Fig. 11: Selecting the Laser — Place the cursor over the laser and
right-click and select emission
desired

3 —Change the Diffraction Grid distance — an obstacle to the beam light;

Fig. 12: Choose one of these slots distance: single (60 μm ) or 3 doubles (30, 40, 50 μm); see calcs below: )

4 — Turn off the laboratory light;

Fig. 13: Turn off ambient light by clicking On/Off Light

5 — Check the gap distance between the grade and the screen;

Fig. 14: To know the distance between the screen and the slot, use the “Anteparo” option — There will be two options available: “Double Slit” and “Screed” — Adjust by clicking on the yellow arrows, so that the difference

6 — View the formed fringes;

Fig. 15: To view the formed fringes, access the “Franjas” option

Fig. 16: Enlarging the scale, clicking on “Ampliar Escala — Enlarge scale”, you will be able to obtain a better view, detailing the first high and low orders, both positive and negative, as shown (note that the scale is in cm)

7 — Determine the wavelength of the corresponding light;

Fig. 17: https://docs.google.com/document/d/e/2PACX-1vQVZetNWC2DJCNHh8Kc_c2KchRk-Dz3VM8CxJnaGEAzEY3HH6BGCxt8C0KEuZ6WvuSgJwacrrYJIN-j/pub

Fig. 18: Although the **red** laser in the literature measures **632.8 nm**, we have, with the acquired measurement of **679**, an error of approximately 7% (seven percent). Not bad, is it?

8 — Experiments nº2 to nº5 — Determination of wavelength of other colors: Orange, Yellow, Green, and Blue incidents — Slot option “Fio de Cabelo” [Wire of hair];

Fig. 19: In the literature the orange laser measures 605 nm. We found 599; Error of 1% (one percent).

Fig. 20: Yellow light ranges from **561 nm (yellow-green) to 586 nm** (yellow-orange), but the maximum peak for oxyhemoglobin absorption is centered at 577 nm (pure yellow). There are several benefits of the 577 nm pure yellow wavelength over 532 nm, 561 nm, or 586 nm wavelengths.

Green laser is 532nm; less than three percent error. Very good!

Fig. 21: GREEN LASER = 532nm — A standard laser diode first generates near-infrared light with a wavelength of 808nm. This is focused on a neodymium crystal that converts the light into infrared with a wavelength of 1064nm. In the final step, the light passes into a **frequency-doubling crystal that emits green light at a wavelength of 532nm —** The 532 nm laser is **one of the oldest and most established diode-pumped solid-state lasers (DPSSLs)**. It revolutionized the laser community and the idea of an all solid state (as opposed to gas gain media) laser was turned into a potential commercial reality.

Blue laser is between 400 nm and 500 nm.

Fig. 22: between 400 nm and 500 nm — What is a Blue Laser? The blue laser is a device that emits a light beam in the wavelength range **between 400 nm and 500 nm**, visible as violet or blue to the human eye. The light beam produced is temporally coherent and can be well-collimated, which allows it to have numerous applications in industry and science.

9 — From now on (Experiments nº6 to nº10) we will modifying the Slit Size — First Red Laser:

Fig. 24: Changing the DUPLA FENDA [DOUBLE SPLIT] to the 250 mm position, making a difference of **320 mm** between the FENDA [SLOT] and ANTEPARO [SCREEN]

Fig. 25: We want to discover what is the distance of the Fenda Dupla I [DOUBLE SLIT I]

Fig. 26: Changing for DOUBLE SLOT (DUPLA FENDA I)

Theses memories calculation are applied to all Experiments nº6 to nº10 below:

Conclusion

The potential of using simulators such as demostrated in this work, Algetec simulators, has a huge potential use in modern education.

We hope that this work, carried out with the greater care and technical rigor, can serve Guide for the Computer Engineer in Brazil, and in Physical Optics, and in the World.

That’s it!

See you soon ! Have a nice day.

Bye! o/

👉 doc: calc. memories

👉 doc: in portuguese