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This came up in an a physics experiment.

The Fourier transform pattern is essentially the diffraction pattern of the transmittivity of the object.

I've tried searching for the definition of what "Fourier transform pattern" is but to no avail. Also, what is this "transimittivity" of an object about? I could only guess that the diffraction pattern refers to an illuminated object by a source at a finite distance away producing an occurred 'phenomenon' as light encounter this object.

Any clarification would be appreciated.

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  • $\begingroup$ Could you read it as a bad translation/analogy of the idea that the F. T. takes a function and decomposes it into its competent parts, such as white light being diffracted into a spectrum of color. Transmittivity could mean various things, depending on the details of the experiment. $\endgroup$
    – user108787
    Commented Aug 29, 2016 at 12:48
  • $\begingroup$ @count_to_10 If I add that this is an optical spatial filtering experiment, would that assist you in telling me more? $\endgroup$
    – Physkid
    Commented Aug 29, 2016 at 13:55
  • $\begingroup$ I searched all the places you probably did, with the same nothing coming up, but at least it's not an analogy and I will search with optics in mind. When I search, I also use the keywords in the images section, half the time people label images with a keyword name included. $\endgroup$
    – user108787
    Commented Aug 29, 2016 at 15:49
  • $\begingroup$ Don't know what you 2 have been looking at, but this was #2 of a google search using the exact question title. The image-pairs ('patterns') are Fourier Transforms of each other. #1 in the search was also pretty good. $\endgroup$
    – sammy gerbil
    Commented Aug 29, 2016 at 18:26

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The diffraction of light is given by the Fraunhofer diffraction integral, provided that the distance of propagation is much larger than the transverse size of the initial optical field. (Over shorted distances one would use the Fresnel diffraction integral.) The Fraunhofer diffraction integral is essentially a Fourier integral. Therefore, one can refer to a diffraction pattern that is seen over such a large distance as a Fourier transform pattern.

The transmittivity of a transparent object should be seen in association with its reflectivity. When light falls on the object, some light is transmitted and some is reflected. The sum of the power that is reflected and that which is transmitted must add up to the power of the incident field. Therefore, the transmittivity and the refelctivity should add up to 1. In accordance with the definition for reflectivity, the transmittivity is the ratio of the transmitted optical power to the incident optical power.

In the context of the diffraction pattern produced by the transmitted light, the transmittivity is a function of the transverse coordinates, giving the transmitted light a specific profile which is then propagated to produce the diffraction pattern. One can think of a thin transparent film having a varying transmittivity over its surface.

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