Joe- I claim no expertise about holograms, but I remember watching my college roommate (Physics Major) making some. As I recall, the two light waves must have both the same frequency AND the same wave phase (called "coherence") in order to cause an interference pattern than can be recorded on film. I don't know how you can get coherent light except from a laser, but maybe someone else can chime in. Due to the difficulty of getting two lasers into coherence, a single laser was used, with the light going thru a splitter to direct the light at the object in two different paths. When the two light paths recombined, the differences in path lengths caused localized out of phase interference, the pattern of which was recorded on film. This is my layman's perspective. Bob Grant ----- Original Message ----- From: Joe Bauman<mailto:josephmbauman@yahoo.com> To: Utah Astronomy<mailto:utah-astronomy@mailman.xmission.com> Sent: Tuesday, June 10, 2008 11:06 AM Subject: [Utah-astronomy] holograms I've been thinking about Chuck's question, basically what I meant by non-laser-produced holograms, and I admit it's hard to describe my idea. That's probably because it's a b.s. idea. But here goes: There are filters, I assume grid-like, that can eliminate most wavelengths of light. If you could put together one that eliminated all but one wavelength, would that one wavelength work like a laser for the purpose of creating a hologram? I think holograms are possible because the laser illuminating the target emits just one frequency of light. When that light hits the target and bounces back to the film, the waveforms from interfering light bouncing back from various objects are preserved on the film. When a laser shines on the developed film, those overlapping waveforms are reconstituted and you see the object that was photographed in 3D. The fact that the laser is an extremely powerful pulse of light has nothing to do with this process; it's the single-wavelength property that is important. My idea is, what if you were to place a piece of photographic film in a shallow box, with the filter in front of the film, in ordinary daylight. Would you get the same effect because only waveform was penetrating the filter? Of course, to actually see the hologram (assuming you really could make one that way), I assume you'd need to illuminate the film with a laser. Thanks, Joe _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com<mailto:Utah-Astronomy@mailman.xmission.com> http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy<http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy> Visit the Photo Gallery: http://gallery.utahastronomy.com<http://gallery.utahastronomy.com/> Visit the Wiki: http://www.utahastronomy.com<http://www.utahastronomy.com/>