• rumborak
In summary, the wavefronts are reconstructed correctly on the other side of the cube, however the cube itself is not present.f

#### rumborak

Hi everybody,

first time post/question, hope you're kind with me :)

I got a somewhat detailed question about holography:
Obviously the very point of holography is to recreate the wavefronts correctly towards the viewer, as in this picture

(thanks to Wikipedia)

My question is, are the wavefronts also correctly reconstructed on the other side, i.e. towards the cube? That is, in the above example, would the points in space that correspond to the surface of the cube, be points in space where the wavefronts constructively interfere, thus resulting in large amplitude?

rumborak

Not the way you have it pictured. But you can make a real image of a hologram - where the image appears in front of the hologram.

Using your diagram, and assuming that the reconstruction beam is planar, then a similar planar beam coming from the right would allow the real image to be seen as viewed from the top of the diagram.

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Hi Scott,

Thanks for responding so quickly. What I'm interested in is not the virtual image though (and I agree that flipping the reference beam would produce the virtual image on the other side), but rather, in the same setup as above where the reference beam is coming from that left, what the wavefronts look like in the area where the cube used to be.
My wild guess is that the wavefronts recreate the point sources that the cube surface used to be, in the positions of that surface. But, can anybody confirm that hunch?

Goodman's book "Introduction to Fourier Optics" has an excellent discussion of this- if you illuminate the hologram with a conjugate reference wave (loosely, the 'opposite direction'), the hologram will produce a real image that is the complex conjugate of the original object:

http://imagebank.osa.org/getImage.xqy?img=cCF6ekAubGFyZ2Usb2wtMjEtMTYtMTI5NS1nMDAx

In general, a hologram will produce both a real and virtual image:

http://cnx.org/resources/b5e5db18ff14bb75a9315309fe8ddc41/Figure_31_05_15.jpg

Certain recording techniques (Gabor holograms) produce both real and virtual images that are in line with each other. the Leith-Upatnieks recording geometry spatially separates the real and virtual image.

Ooooh, thank you very much, Andy! That's exactly what I wondering/hoping for.