Fourier transformation for circular apertures

In summary, the Resolution of the Aperture (in the Electric field of the wave) is the Fourier transformation of the aperture, which can be represented by the equation H(θ)=∫∫G(x)e-i2πθx dx. To find the equation for circular aperture, G(x) is equal to Π(r/2a) and H(θ) can be represented as aJ1(2πas)/s. By using the Fourier property, we can solve for H(θ) by changing θ to θ=λs and using the integral representation J0(z) = 1/2π∫e^-izsinφdφ. The resulting integral over r can be solved by
  • #1
QuarkDecay
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2
Homework Statement
Find the Resolution of a circular aperture with a radius of a
Relevant Equations
Fourier transformations noted below
My notes say that the Resolution of the Aperture(in the Electric field of the wave) is the Fourier transformation of the aperture.
Then gives us the equation of the aperture:

1659133442407.png

and says that for the circular aperture in particular also:

1659133647684.png


My attempt at solving this:

We know that the Fourier transformation in general is :
1659133738649.png


For circular aperture we have G(x)=Π(r/2a). So I thought that if I manage to turn the θ/λ inside the H(θ) equation into an s, (θ/λ=s or θ=λs), then I could say G(x)=Π(r/2a) ⊃ aJ1(2πas)/s, therefore H(θ)= aJ1(2πas)/s, but not this one exactly, because I need to change the s inside the H(θ) equation.

So H(θ=λs)=∫∫G(x)e-i2πsxdx
But now we have an H(λs) instead of an H(θ), so we need to use this Fourier property
1659135074015.png

and this is where I stop because I don't know which is which, and I don't know how this ⊃ works much.
I tried replacing the s with s=θ/λ and say
H(λ*θ/λ)=Η(θ)=aJ1(2πa(θ/λ))/(θ/λ) But I always get a result of
H(θ)=DλJ1(πDθ/λ)/(2θ) and the result is supposed to be this:
1659135029572.png

I always get the λ on the top. And again, when I tried using the
1659135566936.png

I still got the same result, although I'm not sure if I'm appliying this to the H(λs) right, but the book does say that I need to use the property above somewhere.
My main problem is that I can't really solve Fourier transformation and don't understand very well how this ⊃ symbol works
 
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  • #2
I've no idea what [itex]\supset[/itex] is supposed to mean in this context.

Start from [tex]
H(\boldsymbol{\theta}) = \iint_{\mathbb{R}^2} G(\mathbf{x}) e^{-2\pi i \boldsymbol{\theta} \cdot \mathbf{x}}\,dA[/tex] where so far as I can tell from googling the aperture function [itex]G(\mathbf{x})[/itex] is equal to 1 if [itex]\|\mathbf{x}\| \leq a[/itex] and 0 otherwise. By symmetry we can orient the coordinate axes such that [itex]\boldsymbol{\theta} = (0,\theta)[/itex]. Now change to plane polar coordinates [itex](r, \phi)[/itex] to obtain [tex]
H(\mathbf{\theta}) = \int_0^a r \int_{-\pi}^{\pi} e^{-2\pi i r \theta \sin \phi / \lambda}\,d\phi\,dr.[/tex] The integral over [itex]\phi[/itex] can be done by making use of the integral representation [tex]J_0(z) = \frac 1{2\pi} \int_{-\pi}^{\pi} e^{-iz\sin\phi}\,d\phi[/tex] and the resulting integral over [itex]r[/itex] can be done by substitution, noting that [tex]
\frac{d}{dz} (zJ_1(z)) = zJ_0(z).[/tex]
 
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  • #3
pasmith said:
I've no idea what [itex]\supset[/itex] is supposed to mean in this context.

Start from [tex]
H(\boldsymbol{\theta}) = \iint_{\mathbb{R}^2} G(\mathbf{x}) e^{-2\pi i \boldsymbol{\theta} \cdot \mathbf{x}}\,dA[/tex] where so far as I can tell from googling the aperture function [itex]G(\mathbf{x})[/itex] is equal to 1 if [itex]\|\mathbf{x}\| \leq a[/itex] and 0 otherwise. By symmetry we can orient the coordinate axes such that [itex]\boldsymbol{\theta} = (0,\theta)[/itex]. Now change to plane polar coordinates [itex](r, \phi)[/itex] to obtain [tex]
H(\mathbf{\theta}) = \int_0^a r \int_{-\pi}^{\pi} e^{-2\pi i r \theta \sin \phi / \lambda}\,d\phi\,dr.[/tex] The integral over [itex]\phi[/itex] can be done by making use of the integral representation [tex]J_0(z) = \frac 1{2\pi} \int_{-\pi}^{\pi} e^{-iz\sin\phi}\,d\phi[/tex] and the resulting integral over [itex]r[/itex] can be done by substitution, noting that [tex]
\frac{d}{dz} (zJ_1(z)) = zJ_0(z).[/tex]
Thanks a lot...! I'm quite desperate over this problem and I couldn't find the solution anywhere over the web. Been searching for it for three days. Now I hope I can solve the rest of it lol
 
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1. What is Fourier transformation for circular apertures?

Fourier transformation for circular apertures is a mathematical technique used to analyze the diffraction patterns of light passing through a circular aperture. It involves converting the spatial domain information of the aperture into the frequency domain, allowing for a more detailed understanding of the light's behavior.

2. How is Fourier transformation for circular apertures used in scientific research?

Fourier transformation for circular apertures is used in a variety of scientific fields, including optics, astronomy, and medical imaging. It allows researchers to analyze and understand the diffraction patterns of light passing through circular apertures, which is crucial in studying the properties of light and how it interacts with different materials.

3. Can Fourier transformation for circular apertures be used for non-circular apertures?

Yes, Fourier transformation can be used for non-circular apertures as well. However, for non-circular apertures, the mathematical equations become more complex and may require additional techniques, such as numerical methods, to analyze the diffraction patterns.

4. What are the limitations of Fourier transformation for circular apertures?

One limitation of Fourier transformation for circular apertures is that it assumes the aperture is perfectly circular, which may not be the case in real-world situations. Additionally, it does not take into account other factors such as aberrations, which can affect the diffraction patterns.

5. How does Fourier transformation for circular apertures relate to other Fourier transformation techniques?

Fourier transformation for circular apertures is a specific application of the more general Fourier transformation technique. It is used specifically for analyzing circular apertures, while the general Fourier transformation can be applied to a wide range of signals and functions in various fields of science and engineering.

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