All Questions
40
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How to compute the diffraction efficiency of a thin phase grating with arbitrary groove shape?
From Magnusson and Gaylord (1978), the wave amplitudes, $S_i(z)$, of $p$-polarized light for a thin, arbitrary phase grating are given by the equation
$$
\frac{\partial S_i}{\partial z} + \gamma \sum_{...
- 123
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0
answers
30
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Polarization of electric field and its effect on the Poynting vector
To preface, I've little experience with optics. This is a very use-case specific project I'm undertaking. So, if there are any improvements in my method, I'd appreciate it!
I'm working with the vector ...
1
vote
1
answer
69
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Fermat's principle of least time confusion
The link is: https://www.feynmanlectures.caltech.edu/I_26.html#Ch26-F3
Hi, I'm reading Feynman's lecture on Optics: The principle of least time, and I'm wondering if I got what he's saying right. For ...
- 13
1
vote
2
answers
189
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Diffraction limit PSF and angular spectrum method?
I know from the angular spectrum method that given a field $U$ with a wavelength $\lambda$, we can decompose it with Fourier transform.
\begin{equation}
U(x, y,0) = \int \int {\tilde{U}_0(f_x,f_y)} ...
- 444
2
votes
1
answer
152
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A doubt about Kirchhoff's scalar diffraction theory
Scalar diffraction theory assumes a scalar wave equation of the form $$\frac{1}{c^2}\frac{\partial^2u}{\partial t^2}=\nabla^2u$$ where $u(\vec{r},t)$ is a scalar field called the optical disturbance. ...
- 11.8k
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votes
1
answer
350
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Finding angles of second and third order minima given only angle of first order minimum
For the following problem we are asked to find the second and third order minimums of a single slit diffraction experiment at $13^{\circ}$. I tried using the following $$\theta_p=p\cdot\frac{\lambda}{...
- 101
3
votes
5
answers
2k
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Why are shadows sharp close to the object, but blurry farther?
There are quite a few questions about blurry shadows and diffraction on this site, though, none of them specifically answer my question about why shadows blurriness is distance dependent, that is, why ...
- 29k
1
vote
0
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78
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Is energy not conserved in a microscope?
The Point Spread Function (PSF) of an imaging system is its impulse response and defines how a single point on the sample plane is spreaded on the image plane. The simplest model is the one calculated ...
- 937
4
votes
4
answers
212
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What are the microscopic details of diffraction?
In a recent question I asked how double-slit diffraction conserves momentum and the answer was that each photon gets a "kick" from the slits. So my question now is, what does that look like ...
- 1,145
-1
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1
answer
124
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What happens to vertical light in light diffraction experiments?
In single slit experiment, light tends to bunch up vertically the more it spreads out horizontally. Why does this happen?
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6
votes
3
answers
2k
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Why do we need collimated light on a diffraction grating?
In all of the images I've seen from a spectrometer, there's always a collimating element that places an image at infinity so as to have parallel rays hitting a diffraction grating. But why do we need ...
- 637
4
votes
2
answers
274
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How to set up the right model for solving diffraction numerically?
The diffraction of waves in free space is governed by the sourceless Helmholtz equation
$$\nabla^2u +k^2u=0$$
There is a well stablished solution called Kirchhoff´s diffraction integral (KDI) and it´...
-1
votes
1
answer
153
views
Is there an analytic expression for the Fresnel pattern from a circular aperture?
I am interested in the Fresnel diffraction pattern (over an entire observation plane, not just the value on-axis) due to a plane wave incident on both square and circular apertures.
I have two optics ...
- 165
0
votes
1
answer
253
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Steps to calculate the near-field diffraction pattern after an aperture (for distances so close that the Fresnel regime is not valid)?
This question has arisen out of a previous question regarding the various approximations in optical diffraction theory, and when they can each be applied.
I would like to know the steps that must be ...
- 165
4
votes
1
answer
825
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Does Fraunhofer diffraction also automatically imply that the Fresnel approximation is simultaneously satisfied?
I am confused about the regimes of validity for the Fresnel and Fraunhofer diffraction approximations, and would appreciate some clarification. Let's say we are interested in calculating the field $...
- 165