Discovery is not an invention. The invention may be a long-sought solution to a problem posed using known phenomena or mechanisms. The discovery of themes and the discovery that it is an effect that no one knew anything about, and therefore did not seek, could not seek. You can only search for what is known. Like all finds, a discovery can be big or small. But it opens, as a rule, to persons more or less prepared, who can immediately appreciate that what they observe is not only very curious, but most likely something completely unknown.
Was the discovery of electricity big in those days when it was only known about it that a woolen stick attracts pieces of paper? In this form, this discovery lasted for millennia. No one saw any benefit in it and no one knows the name of the author or authors who first noticed this phenomenon. And now, without electricity, we cannot take a step. The names of Faraday or Tesla, who did a lot to develop our knowledge of electricity, are known to almost everyone. What unites all discoveries is that we always see something unusual in them and would like to know its cause - even when it is of no use to us.
The above is just a saying. When some movement of the prism on the substrate while working with the laser, the prism suddenly "flashed", like a switched on light bulb flashes. Of course, the effect was not so strong, but, nevertheless, it was strong enough to interest and start looking for its cause. Perhaps this was due to the fact that the laser beam fell on the inner surface of the side face and the reflected light caused the entire prism to "flash"? But everything turned out to be the opposite. Another "flash" was noticed when the laser beam touched the outer surface of the face.
It's strange. When the laser beam hits the end face perpendicularly, a rather bright luminous point appears in this place. The second bright point occurs at the point where the beam exits through the opposite end face. Both of these luminous points illuminate all facets of the prism quite well from the inside.
Photo 1. The upper thick line inside the prism - it is a luminous trace of a laser beam passing through the ends of the prism. Lower - this is a reflection of this trace in the lower edge. It can be seen that the ends of the prism glow quite brightly.
If you direct the beam so that it is reflected from the inside from one of the side faces, then another luminous point appears, illuminating the edges of the prism from the inside. But this effect is insignificant compared to the flash that is obtained when illuminated with a laser beam touching the side edge from the outside. In this case, from the opposite side of the prism, no bright points are even visible at all, which could illuminate the prism from the inside. But the entire prism and especially the end faces become comparatively very bright. The way the beam touches the side face also plays a role. When the direction of the beam is longitudinal, the effect is most pronounced. If the direction of the touching ray is perpendicular to the plane passing through the central axis of the prism, the effect is almost imperceptible.
How else can the beam touch the prism? The ends remained. And here the main surprise awaited. In this case, the flash is much stronger than when the beam touches the lateral plane.
Photo 2. The laser beam touches the front end of the prism. The direction of the beam is almost parallel to the front end, the point of contact is almost invisible, but the entire prism is, as it were, illuminated from the inside. Please note: in photo 1, the place where the beam enters the prism is clearly visible, but the prism itself shines much less.
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The touching direction does not matter. The flash is maximum - even when the ends are not sanded and appear opaque!
How to explain this phenomenon? The only thing that comes to mind is resonance. Of course, for a couple of centuries, light has been represented as a wave. For some time now it has been presented as transverse waves. But transverse waves propagate across the direction of vibration (along the beam). Can this explain the bright uniform glow of exactly the ends?
Imagine an ordinary drum, one of the simplest musical instruments. He has the most sensitive ends. And it is they who most strongly emit sound waves. In this sense, the transparent prism resembles a drum. But the analogy ends there. The drum side is not sensitive.
Has anything like this been observed? When does light "penetrate" across the direction of the rays? I know an excerpt from a physics textbook [H. Vogel. Gerthsen Physik, Springer-Verlag, Berlin Heidekberg, 1995, p. 486] related to total internal reflection:
“More detailed (close?) Observation shows us the limits of the possibilities of geometric optics. If we take a fluorescent liquid as a less dense optical medium, then, despite the full internal reflection, a thin fluorescent layer can be observed. A small amount of light, therefore, does pass through. But the thickness of this layer is equal to only a few wavelengths; the intensity decreases exponentially with distance from the media boundary."
This passage appears to be talking about a certain amount of light traveling perpendicular to the direction of the beam. But the textbook interprets this as a quantum mechanical effect.
It seems to the author that something similar is happening here. The ray does not enter the prism, it only reflects from its surface. But, nevertheless, the light somehow "penetrates" into the prism and it all glows. It can be assumed that the light enters the prism in a direction approximately perpendicular to the beam.
One can imagine that in a laser beam the light vibrations are directed across the beam in all directions. Therefore, with a perpendicular entrance of the beam, as in photo 1, all directions are equal and therefore the glow of the ends is insignificant. When the beam "touches" the interaction occurs lateral, therefore, the influence of that part of the light, the vibrations of which are directed along the tangent to the beam, can prevail. Therefore, here mainly only transverse vibrations are transmitted, tangent to the laser beam and simultaneously parallel to the plane (face) of the prism.
The excitation of transverse vibrations explains to some extent even the fact that the direction of contact of the ray on the lateral face should be longitudinal. At the ends, the direction of contact of the beam should not matter, as it was shown in the experiment.
Of course, this is only a guess. New here would be the propagation of oscillations across the beam and their capture of the entire volume of the transparent body. Some kind of interaction with all the material that the ray only touches?
With a strong desire, the described phenomenon can be interpreted simply as light scattering. But it would then be a very strange "dispersion". The amount of light scattering, if it were the cause of the luminescence of the prism, apparently, would have to be equated to the magnitude (power) of the luminescence of the prism. How then to explain that the magnitude of this scattering is much less when the ray passes through the entire length of the prism inside it, compared to when the ray only touches the material of the prism, not entering it at all? After all, scattering should occur precisely when passing through the prism material, while overcoming the resistance to the movement of the beam? Therefore, it seems to the author that the discovered effect has something in common with the phenomenon of resonance.
Johann Kern, Stuttgart
