Lunar Surface hologram

Topics not fitting anywhere else.
Dinesh

Lunar Surface hologram

Post by Dinesh »

Martin wrote:The practical side of the setup is quite a different ball game. I don't see how to reach equal path lengths with a broadband ("white") light source. The requirements on precision would be far too stringent in my opinion.

However, if the light source becomes narrow, things will change dramatically. If the setup implied the use of a single-frequency laser, the whole thing would be changed into a device of making reflection gratings holographically.
In that respect I think this patent isn't very far from Denisyuk.
I didn't read this carefully enough, I was assuming he was using laser light. I saw the same difficulty with path lengths. The coherence length of white light from an incandescent lamp is about 8 microns, or about 16 lambda. The only way this kind of precision can be obtained is with interferometry. But, any interferometric system included in the geometry would increase path lengths and so seem self-defeating.

I also agree this is not far from Denisyuk. I think the real problem is: do you define the system by the observable result or by the physical result? If the latter, A Lippman can be considered simply as Denisyuk with an on-axis reference beam. If the former, then the three dimensional appearance of a Denisyuk hologram is very different from a Lippman photograph. In fact, thinking a bit further, if you put a small transparency in the path of an on-axis incoming beam in a Lippman/Denisyuk geometry very close to the plate, and the transparency was mostly clear (so not too much off-axis scattering), then you'd get an image of the transparency which may be considered holographic or Lipmann, but would be projected outside the surface. However, this is exactly what Gabor did! Gabor states that "The print was replaced in the apparatus, backed by a viewing lens..., and the image formed was observed". So, Gabor reconstructed his first hologram by re-illuminating it with the mercury arc lamp. Wonder what he would have seen had he taken it out in the sun?
Martin

Lunar Surface hologram

Post by Martin »

Dinesh wrote:I also agree this is not far from Denisyuk. I think the real problem is: do you define the system by the observable result or by the physical result? If the latter, A Lippman can be considered simply as Denisyuk with an on-axis reference beam. If the former, then the three dimensional appearance of a Denisyuk hologram is very different from a Lippman photograph.
That's an interesting distinction.
I'd like to add the history "dimension". The question then becomes, to what extent findings in and of the past may turn into something entirely new over the years.
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