Holographic effect

These are all of the old posts from the first two years of the forum. They are locked.
Updated: 2005-03-28 by HoloM (the god)
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JohnFP

Holographic effect

Post by JohnFP »

I have always wanted to set up a table such that a raw laser crosses the plateholder plane and hit a small mirror for the object and bounces right back down the beam. Basically an on axis grating. But you would hold the plate by hand and move it around in the beam rotating and changing the angle. Slow and fast. I believe if you got the speed correct it would yield a very interesting diffration pattern.




Bob

Holographic effect

Post by Bob »

I remember once seeing a reflection hologram that was made by a scanning "raw beam" hitting a hand held plate. The image recorded was that of the palm of the hand! I believe it was at the Lake Forest Symposium on Display Holography, possible in 1985.
Dinesh

Holographic effect

Post by Dinesh »

It's possible. If the beam power is high enough and the film sensitive enough. A rough back-of-an-envelop calculation:
A raw beam from a laser has a cross section of about 1 sq mm or 1/100 sq cm. A 400 mW/sq cm would therefore deliver 400*100 mJ/sec or about 40 J/sec over an area of 1 sq mm. If the film sensitivity is approx 50 uJ (8E75 I believe had this sensiivity), then an exposure of (40/50)*10^(-3) or about a millisecond would record. So long as the object did not move by more than an order of lambda in 1 millisecond, you'd get a hologram. This translates to (5*(10^(-7))/(10^(-3) which works out at about 0.5 cm/sec or so. This with only a 400 mW beam at 500nm. A more powerful beam would reduce the speed sensitivity even more, or perhaps I mean increase it. well, it would make life easier in terms of recording a moving object. Now, and I'm probably really stretching here, if you heartbeat is 60/sec, then your skin pulsates through a complete cycle in 1/60th of a second. Assume that the "amplitude" is 1/10mm, then it's travelling 1/10 mm in 1/120 sec (half the period) which gives 12 mm/sec of skin velocity. Of course, you'd need to take into account the direction of movement. Given the back-of-an-envelop rough assumptions characteristic of this calculation, I propose that 0.12 cm/sec is not that far off 0.5 cm/sec.
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