Quantum tunneling and MM

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by jrich</i>
<br />What makes a laser useful is that the wave fronts also propagate in the same direction and this is also required AFAIK for the waves to be considered "coherent".<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">No, as I explained, light from any light source ends up coherent even though the emissions are not synchronized. But normal light contains many different wavelengths; and of course, different wavelengths cannot be coherent. So coherence is a more prominent and useful property in laser light.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">In any case I have never seen an explanation for how this directionality is maintained over vast distances if light is a pure wave. When the particle nature of light is assumed the explanation is trivial.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">That explanation is easy. Place two rocks some distance apart in a pond, sticking up above the surface. From some distance away, drop another rock into the water, sending out circular wavefronts. Watch as the wavefronts go past the rocks. If the rock spacing is large compared to the wavelength, the rocks serve as a gate that allows only a portion of the wavefronts through. On the other side of the rocks, one finds an essentially linear, directed set of wavefronts with the width of the gate.

The same is true for flashlight beams and other restricted aperatures. As long as the gate size does not approach the wavelength, light is easily directed in this way. Lasers are simply an extreme application of this principle. Even for lasers, the beam spread cannot be made zero (as it easily could for particles), but can be made small enough that a laser beam to the Moon and back spreads only about a kilometer. -|Tom|-

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">In any case I have never seen an explanation for how this directionality is maintained over vast distances if light is a pure wave.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
The light in a laser bounces back and forth millions of times before exiting one end of the apparatus (the half silvered one). This makes the apparatus equivalent to a tube of extremely great length ... so what exits the tube stays together for long distances. Most of the energy is lost to the sides either being absorbed or escaping to be absorbed by the lab walls or experimenters ;o) If most of the energy wasn't absorbed (wasted), it would all come out at the end at different angles and spread rapidly at the exit. By absorbing the stray energy all that's left is what is going straight.

You could do the same thing with an ordinary flashlight if you had a really straight tube a million miles long and shined it down one end. Note that if you did it with a flashlight almost no light would appear at the end of the tube because most would have been absorbed by the walls ... but what did emerge would be real staight. But if the inside walls were mirrored, all the light would all come out at the end spreading in the normal fashion after bouncing down the tube helter-skelter.

EBTX,

What you say seems valid. One exception I believe is the fact that in the laser the absorbtion goes to exciting the medium and isn't wasted, hence its efficiency is sustained where as your flashlight example the absorbtion is a simple loss.

So laser light becomes straight but remains intense. In fact concentrated since dispersed light becomes focused and straight.

"Imagination is more important than Knowledge" -- Albert Einstien

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">in the laser the absorbtion goes to exciting the medium and isn't wasted<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Could be so. I looked up some info here.
From:
library.thinkquest.org/J001741/laserWeapons.html?tqskip1=1

Lasers have only a 1-30% efficiency, which means that only that much of the energy pumped into the laser emerges out of the laser. Most of that wasted energy is released as heat. In powerful lasers, this heat becomes very intense, shattering the laser's mirrors. Elaborate cooling systems must be devised, which often come out very large and very heavy.

EBTX,

Perhaps I was not clear in what I meant but certainly I new lasers were not overly efficient. My point was that the reflected energy in the chamber that bounces off the mirrows and walls goes back into the excitation process and isn't totally wasted. Whereas in your flash light what doesn't come out the end coherent is wasted.

To make my point compare the efficiency of your flashlight with a long tube that will result in a 1 km expansion beam to the moon and back to that of your laser. I think you will see the laser is many magnitudes more efficient.

"Imagination is more important than Knowledge" -- Albert Einstien

Tom,
<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by tvanflandern</i>
<br /><blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by jrich</i>
In any case I have never seen an explanation for how this directionality is maintained over vast distances if light is a pure wave. When the particle nature of light is assumed the explanation is trivial.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">That explanation is easy. Place two rocks some distance apart in a pond, sticking up above the surface. From some distance away, drop another rock into the water, sending out circular wavefronts. Watch as the wavefronts go past the rocks. If the rock spacing is large compared to the wavelength, the rocks serve as a gate that allows only a portion of the wavefronts through. On the other side of the rocks, one finds an essentially linear, directed set of wavefronts with the width of the gate.

The same is true for flashlight beams and other restricted aperatures. As long as the gate size does not approach the wavelength, light is easily directed in this way. Lasers are simply an extreme application of this principle. Even for lasers, the beam spread cannot be made zero (as it easily could for particles), but can be made small enough that a laser beam to the Moon and back spreads only about a kilometer. -|Tom|-
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
One would think a general wave phenomenon like this would be well studied and explained. Is there a formula for determining how quickly a wavefront in any medium will spread out? I would guess medium particle size, coefficient of friction, medium density and some other variables could be used to predict things like wave propagation speed and wavefront spread. Would such a formula be able to tell us anything about the elysium that we don't yet know?

Back to the original topic. I wonder if quantum tunneling of light can best be explained by realizing that objects which are assumed to be opaque to light perhaps are not. That the elysium is enmeshed within the objects that are used in the experiments and so there is a probability that a portion of the wavefronts will propagate through the material with enough amplitude to produce the effects that are seen.


JR