Uhum,
Going back to the moon... I keep wondering how they are sending the holos back home...
Lunar Surface hologram
Lunar Surface hologram
I don't believe the beams is a Denisyuk system ever have equal amplitudes, because there's always going to be some absorption and scattering in the emulsion.Dinesh wrote: The crux of the hypothesis is that there needs to be standing waves within the medium. However, in order to create standing waves, the beams in both directions need to be of equal magnitude. If they are not, there is a travelling wave component, the planes would move slowly, depending on the beam ratio. Depending on the sensitivity of his plates, any such motion would result in loss of efficiency. Therefore, using specular reflection would have been fairly important to ensure that the beam amplitudes were equal.
But my real issue is the statement that "If they are not, there is a travelling wave component, the planes would move slowly, depending on the beam ratio." What "planes" are you talking about here? Certainly not the fringes being recorded. Are the "planes" you mentioned those of the "traveling wave component"? I can see that being part of the mechanism that decreases fringe visibility with a decrease in beam ratio. Is that what you're trying to say?
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Joe Farina
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Lunar Surface hologram
I found the papers by Hoffman et al. (1965) and Stroke and Labeyrie (1966). The one by Hoffman is below, I will attach the Stroke paper in another post. To make a long story short, Hoffman doesn't mention anything involving white-light reconstruction. The recording geometry is for a split-beam reflection hologram, yet they are reconstructing the hologram like a transmission hologram, using a laser, except (apparently) from the front rather than from behind. So perhaps they never noticed that white light (from the sun or a flashlight) could reconstruct the hologram? Or perhaps a good reflection hologram wasn't recorded in the first place? No reference is made to Denisyuk, apparently this is strictly an offshoot from L & U (as noted in the references). After Upatnieks duplicated the Hoffman work (c. very late '65 or very early '66?) he was "astonished to glance at the hologram in sunlight and see the 3-D image formed in white light."
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Joe Farina
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Lunar Surface hologram
The paper by Stroke and Labeyrie is below. This does seem to be the first published account of split-beam reflection holography. Since the authors were with the U. of Michigan, the work of L & U must have been fully in mind, yet this is not in the references. They reference Lippmann, Ives (Lippmann photography), Gabor, Denisyuk, and the above work by Hoffman et al.
The first figure (1a) makes it clear that additional object light comes from either side of the plate, so it looks like they have two object beams in addition to the reference beam. The hologram in the photograph (the grasshopper) is, disappointingly, of a Kodachrome transparency, but Figure 1a does show a three-dimensional "object."
The first figure (1a) makes it clear that additional object light comes from either side of the plate, so it looks like they have two object beams in addition to the reference beam. The hologram in the photograph (the grasshopper) is, disappointingly, of a Kodachrome transparency, but Figure 1a does show a three-dimensional "object."
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Lunar Surface hologram
The reason why the above mentioned paper didn't cite L & U was because of bad blood between Stroke and Leith. See the Johnston book for details.
"We're the flowers in the dustbin" Sex Pistols
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Joe Farina
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Lunar Surface hologram
No thanks.Ed Wesly wrote:The reason why the above mentioned paper didn't cite L & U was because of bad blood between Stroke and Leith. See the Johnston book for details.
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Dinesh
Lunar Surface hologram
Not completely. Consider that you have two traveling waves going through the medium. This is a standard recording setup. The two traveling waves travel in such a way as that the phase at any given point inside the medium is constant, creating a fringe or a Bragg plane, which is the locus of iso-phase along a surface. However, the two waves are traveling waves. One way of thinking about this, that I've mentioned elsewhere, is to consider two clocks traveling towards the medium. As the clocks propagate, the hands rotate, with a rate of k. When they enter the medium, at any given position, the position of the hands of each clock will depend on the position of the clock itself, the angle of the clock hand from some arbitrary zero being kx where x is the distance traveled (I'm ignoring the effects of refractive index, which will cause the hands of the clock to suddenly jump backwards when they enter the medium). However, the difference between the hands of the clocks at any given position, the angle between the hand of the "ref clock" and that of the "obj clock", will be constant, assuming proper coherence.That angle will determine the strength of the actinic reactionBobH wrote:What "planes" are you talking about here? Certainly not the fringes being recorded. Are the "planes" you mentioned those of the "traveling wave component"? I can see that being part of the mechanism that decreases fringe visibility with a decrease in beam ratio. Is that what you're trying to say?
Now, if you have a standing wave caused by two separate counter-propagating beams of equal magnitude (not one reflected back on itself via a mirror) , then you have a classic standing wave pattern. The clocks are effectively "frozen" in place and the actinic reactions will depend on the position of the hands of the clock. So, for sake of example, the maximum actinic reaction takes place at "6 o'clock" and "12 o'clock" (zero and pi) and the minimum at quarter past and quarter to the hour (pi/2 and 3*pi/2). This is not interference, in the usual sense that holographers know the term, it's an effect of phase reversal of two counter-propagating beams. Yes, this is interference in the strict sense, but I'm trying to separate out two beam interference from the classic standing wave phenomenon. However, if you now have two sets of clocks, one set "frozen" in place and one set propagating, then the propagating component will "interfere" with the incoming beam to cause an additional set of planes, providing that there is a phase relationship between the incoming beams. If the standing wave is caused by reflecting light from a mirror, I don't think there will be such an interference (I don't think, I haven't completely worked out the phase relationship if only one beam is present). However, if the standing wave is caused by two counter-propagating beams of unequal magnitude, then it may be possible that there are two effects going on: one set causing standing waves and one set causing interference. The strength of this effect will depend on the phase and velocity of the traveling component.
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Dinesh
Lunar Surface hologram
Glad you asked! Actually they have these pods on the moon maintained by robots that telepods the holograms back to earth. You didn't think "The Fly" was just a science fiction movie, did you? No! no! It was a training film for the robots on the moon warning them they could end up as robot-flies if they weren't careful. It was telling them to be afraid! Be very afraid!Arturo wrote:Uhum,
Going back to the moon... I keep wondering how they are sending the holos back home...
We at Winky Truth and Facts labs (WTF labs) have procured a picture of a robot feeding a hologram into a pod. Note the use of the laser to ensure that the hologram is OK, a final QA check!
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Lunar Surface hologram
Dinesh, you've got me completely confused. One moment it's not interference, the next sentence it is. Are you saying that fringes are moving when the beam ratio is other than 1? If so, how fast?
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Dinesh
Lunar Surface hologram
I'm saying that there is a phase relationship between the traveling component and the incoming wave. This is not the same relationship as two waves going in opposite directions with equal amplitude.
The phase relationship between the two waves of equal amplitude causes local maxima that are not the amplitude of either wave - the classic standing wave. In this case, the E vector rises to a value, A, dependent on the x position. Thus, A = cos(kx)cos(wt); for a wave of wavelength 500nm {k= 12.566 (micron)^(-1)} , when x=500/6 nm , the maximum value of the E vector oscillation is +/-0.86 of the amplitude. In a standing wave, it cannot go any higher. This is a special kind of interference where at any given point x, the E vector cannot go higher than cos(kx). In two beam interference, both beams oscillate at their full amplitude, but due to the phase relationship, at any given position x, the E vector values add, due to the principle of superposition, giving a total disturbance whose E vector value, A(tot) is given by the "interference equation" A(tot) = A(1) + A(2) + 2{A(1)*A(2)}{cos<phase difference>}. As you see, the E vector value, A, at any position x is different in each case. Their both interference effects, but the total value of E is given by two different expression, in the two cases.
In a case where there are two counter-propagating waves of unequal magnitude, different values of the amplitude, there is a standing wave, but superimposed on this is a traveling wave component. This traveling wave component also has a phase relationship with the incoming wave. Thus this traveling wave component will generate a series of iso-phase planes. These iso-phase planes will also obey I = I(1) + I(2) + 2[I(1)*I(2)]^(0.5){cos<phase difference>}, but the <phase difference term> may be time dependent.
The phase relationship between the two waves of equal amplitude causes local maxima that are not the amplitude of either wave - the classic standing wave. In this case, the E vector rises to a value, A, dependent on the x position. Thus, A = cos(kx)cos(wt); for a wave of wavelength 500nm {k= 12.566 (micron)^(-1)} , when x=500/6 nm , the maximum value of the E vector oscillation is +/-0.86 of the amplitude. In a standing wave, it cannot go any higher. This is a special kind of interference where at any given point x, the E vector cannot go higher than cos(kx). In two beam interference, both beams oscillate at their full amplitude, but due to the phase relationship, at any given position x, the E vector values add, due to the principle of superposition, giving a total disturbance whose E vector value, A(tot) is given by the "interference equation" A(tot) = A(1) + A(2) + 2{A(1)*A(2)}{cos<phase difference>}. As you see, the E vector value, A, at any position x is different in each case. Their both interference effects, but the total value of E is given by two different expression, in the two cases.
In a case where there are two counter-propagating waves of unequal magnitude, different values of the amplitude, there is a standing wave, but superimposed on this is a traveling wave component. This traveling wave component also has a phase relationship with the incoming wave. Thus this traveling wave component will generate a series of iso-phase planes. These iso-phase planes will also obey I = I(1) + I(2) + 2[I(1)*I(2)]^(0.5){cos<phase difference>}, but the <phase difference term> may be time dependent.