Computer Simulation of Fresnel Diffraction

In summary, the Fresnel Diffraction formula describes the diffraction of light at various points in space, taking into account the aperture size and the distance between the source and the observer. The integration process used to solve the formula is the Trapezoidal Rule. The use of the Fresnel Diffraction formula can lead to long computing times for larger images, so the Fourier Transform is recommended. While there are many free implementations of the Fourier Transform available, it is not necessary to implement it yourself. The function FFT in MatLab is a common choice, although it is an approximation according to Wikipedia. There may be other ways to transform the equation without using an approximation.
  • #1
ecastro
254
8
Considering this system (from Wikipedia),

685px-Diffraction_geometry.svg.png


The Fresnel Diffraction at x, y, and z is

##E \left(x, y, z\right) = \frac{z}{i \lambda} \int \int^{+\infty}_{-\infty} E \left(x', y', 0\right) \frac{e^{ikr}}{r^2} dx' dy'##

where ##r = \sqrt{\left(x - x'\right)^2 + \left(y - y'\right)^2 + z^2}##, ##E \left(x', y', 0\right)## is the aperture, and ##i## is the imaginary unit. The integration process I used to solve the integral is the Trapezoidal Rule (I don't know any good processes that is not step length dependent, and this is the one I am most familiar with).

As of now, the aperture size is infinite, so the image at ##z = 0## is unobstructed. I tried using the Fresnel Diffraction with this image:

Sample.png


And this was the corresponding Fresnel Diffraction at 4 meters with a wavelength of 700 nm:

new_sample.png


Is this correct?
 
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  • #2
Anyway, I was told it was correct. However, the computing time for larger images are extremely long, so I might need the Fourier Transform. Can anyone help me on how to implement it?
 
  • #3
As a general rule, you don't implement the FFT yourself (except for educational purposes) :)
There are myriad free implementations of it out there, e.g. FFTW for C++ (the only one I have ever dealt with).
 
  • #4
So, I think it is alright if I used the function FFT of MatLab. But (according to Wikipedia, again), the function they used in the Fourier Transform is an approximation. Is there such a way that the equation at my first post can be transformed without the approximation?
 

1. What is Fresnel diffraction and why is it important?

Fresnel diffraction is a phenomenon that occurs when a wave passes through a small aperture or around an obstacle. It is important because it allows us to understand how light behaves around objects and helps us to design and optimize optical systems.

2. How is computer simulation used for Fresnel diffraction?

Computer simulation is used to model the behavior of waves passing through small apertures or around obstacles, which allows us to predict the resulting diffraction patterns. This is especially useful when designing complex optical systems.

3. What factors are important in a computer simulation of Fresnel diffraction?

The most important factors in a computer simulation of Fresnel diffraction include the size and shape of the aperture or obstacle, the wavelength of the incident light, and the distance between the aperture or obstacle and the observation point.

4. How accurate are computer simulations of Fresnel diffraction compared to real-world experiments?

Computer simulations of Fresnel diffraction can be very accurate if the simulation is based on accurate mathematical models and the input parameters are set correctly. However, there may be some discrepancies between the simulation and real-world experiments due to limitations in the simulation software or other factors.

5. What are some applications of computer simulation of Fresnel diffraction?

Computer simulation of Fresnel diffraction has many practical applications, including in the design of optical systems such as lenses and microscopes, in the study of diffraction patterns in microscopy and astronomy, and in the development of new technologies such as holography and optical data storage.

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