Optics cornu spiral and diffraction

In summary, the conversation revolves around using the Cornu Spiral to solve a problem involving Fresnel diffraction. The problem involves finding the irradiance of the diffraction pattern at a certain distance using a specific wavelength of light. The person is struggling to understand how to use the Cornu Spiral and is seeking help online and from their textbook. They are unsure of where to start and suggest using the positions of the minima to assist with scaling the spiral. The conversation ends with a suggestion to use computer programs like Mathematica to solve the problem more easily.
  • #1
lazytofindname
3
0
Hi, i am in second year of university and doing optics
I have a questions in one ofmy assignment :

Fresnel diffraction is observed behind a wire 0.37 mm thick, which is placed 2 m from the light source and 3 m from the observation screen. If the light of wavelength 630 nm is used, find, using Cornu spiral, the irradiance of the diffraction pattern at the screen on the axis. Express the answer as some number times unobstructed irradiance.

The problem is I have no idea out to use the cornu spiral, i looked everywhere online and nobody really explains it
In my textbook they don't really explain it either
I know I'm supposed to put the beginning of my work but i don't know where to start
I think I'm supposed to find the variable u and plot in on the spiral but it doesn't make any sense for me..
 
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  • #2
Whilst I can't claim to have tried it, the description of using the Cornu Spiral seems to be reasonably clear in this link.
It does seem to show how to work out the resultant vector from all contributions of elements around an edge, using the spiral curve. Hope it helps. At least you could read through it and it may help a bit.
If you are having a difficulty actually scaling the spiral to your case (that could be your problem?) then I suggest you cheat a bit and use the positions of the minima (from simple diffraction theory) to show you where you expect to be on the spiral and that should help.

On the bright side, it's easier nowadays to use the integrals straight and the graphical method is no longer needed, now we have computers with Mathematica!.
 

1. What is the optics cornu spiral and how is it related to diffraction?

The optics cornu spiral is a graphical representation of the diffraction pattern produced by a point source of light. It shows the intensity of the light at different points in the diffraction pattern, with the intensity decreasing as the distance from the center of the pattern increases. This spiral is a useful tool for visualizing and understanding the diffraction phenomenon.

2. How does diffraction occur?

Diffraction occurs when a wave, such as light, encounters an obstacle or passes through a narrow opening. The wave bends around the edges of the obstacle or opening, causing interference patterns to form. This results in the diffraction pattern, which can be observed and studied using tools like the optics cornu spiral.

3. How does the size of the obstacle or opening affect the diffraction pattern?

The size of the obstacle or opening affects the diffraction pattern by determining the amount of bending that occurs in the wave. A smaller obstacle or opening will result in a wider diffraction pattern, while a larger obstacle or opening will produce a narrower pattern. This can be seen in the changing shape of the optics cornu spiral as the size of the obstacle or opening is altered.

4. What is the importance of studying diffraction and the optics cornu spiral?

Studying diffraction and the optics cornu spiral is important in understanding various phenomena, such as the behavior of light in different mediums and the properties of waves. It also has practical applications, such as in the design of optical instruments and devices, and in the field of optics and photonics.

5. Can the optics cornu spiral be used to predict the diffraction pattern for any obstacle or opening?

Yes, the optics cornu spiral can be used to predict the diffraction pattern for any obstacle or opening, as long as the size and shape of the obstacle or opening are known. By analyzing the spiral, the intensity and shape of the diffraction pattern can be determined, providing valuable information for various scientific and technological purposes.

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