Real-time holography article in this week's Nature

[Guillermito]

"Holographic three-dimensional telepresence using large-area photorefractive polymer". One image every 2 seconds. Not bad.

http://www.nature.com/nature/journal/v4 ... 09521.html

First time I see Star Wars cited in a scientific paper

Guillermit

[Dinesh]

"Holographic three-dimensional telepresence using large-area photorefractive polymer". One image every 2 seconds. Not bad.

http://www.nature.com/nature/journal/v4 ... 09521.html

First time I see Star Wars cited in a scientific paper

Guillermit

It's because they use a pulse laser to write the slits. The advantage of the material is that it's electrically refreshable, as opposed to, say Lithium Niobate or KDP, which is optically refreshable. However, the material needs a very large voltage applied to the plate before it can record, something of the order of 7000 - 9000 volts. If you notice, the decay time is longer than the recording time.

Basically, the material acts as a sort of "optical capacitor", charging to record and discharging to erase. Light causes a charge separation which is enhanced by the applied voltage (without the applied voltage the charge separation would be too weak) which in turn causes an index change. Depending on several factors, there is a time constant like the RC time constant for capacitors so when the voltage is taken off the polarisation disappears and so the index change is gone, effectively erasing the hologram. The molecules are very "stiff" and so require a large voltage to create sufficient (electrical) polarisation for a decent index change. The hologram itself is a standard multiplex or lenticular geometry with a number of slits recorded across the plate. It takes 2 seconds to record all the slits using a pulse laser for recording.

[awerby]

People have been pointing out these large-scale projected illusions to me and telling me that these are holograms. The people producing them call them "holographic". I don't think true holography is actually quite (or even nearly) there yet, but I'm not sure how these are done. I suspect that this is basically the old magician's trick, done with parabolic mirrors, but there's no technical information given. Anybody want to help me out, and tell me how these are done? Here are some links:

http://www.klips.net/video/nlhfhr-hologram-concert.html
http://www.youtube.com/watch?v=goChPAcicZU
http://vimeo.com/7125445

Does this have anything to do with true (interference-pattern) holography?

Andrew Werby
juxtamorph.com

[BobH]

The links Andrew posted above show projections onto large sheets of transparent material, that probably have holographic structures on or in them to provide diffusion only when hit with the projection from a specific angle. There's no stereopsis with the images.