question about light dispersion

[gib65]

There's this sentence from the wikipedia article on dispersion:

 

"refractive index n decreases with increasing wavelength λ. In this case, the medium is said to have normal dispersion. Whereas, if the index increases with increasing wavelength the medium has anomalous dispersion."

 

I'm not sure if I was following this correctly, but are they saying that different colors of light will refract more than other colors depending on the medium. That is, for some media, red refracts more than blue, but in other media, blue refracts more than red?

[swansont]

There's this sentence from the wikipedia article on dispersion:

 

"refractive index n decreases with increasing wavelength ?. In this case, the medium is said to have normal dispersion. Whereas, if the index increases with increasing wavelength the medium has anomalous dispersion."

 

I'm not sure if I was following this correctly, but are they saying that different colors of light will refract more than other colors depending on the medium. That is, for some media, red refracts more than blue, but in other media, blue refracts more than red?

 

Yes, and it also means that a pulse of light that has some range of wavelengths will tend to spread out under normal dispersion and compress under anomalous dispersion.

[pioneer]

The reason this occurs is the incoming light generates an electric field within its propagating sine wave. Charged particles within the medium try to align with this electric field. But being matter, there is a time delay. But since both are at the same electric field energy level, the two waves will add. The resultant composite wave maintains the frequency of the incoming light, but the composite wave will be different in wavelength. The refractive bend sort of compensates for the composite wavelength change, so the same number of frequency cycles occurs.

 

If you look at energy as a function of wavelength, different frequencies do different things to matter. Red will not affect covalent bonding, but UV will, etc..This connection sets the type of charge re-actions. Some energy level interactions are easier to pertubate in different type of materials.

 

With the hotter wavelengths, which can break bonding, the separated negative and positive charges, if they both try to align with the field, will end up at opposite sides of the sine wave of the light's electric field. They have their own charge attraction. So their amplitude is smaller. The longer wavelengths affect vibrational energy level which does not affect chemical bonding. These align easier and can generate a higher amplitude. The higher amplitude gives more umph to the wave addition with the light.

 

Seeds for the imagination

 

Here is an interesting scenario. Since the charges are out of phase, typically going slower, under certain circumstance they will can get ahead of the incoming wave. A good analogy is a race around a running track. The light gets out to an early lead, with the matter lagging behind. If the race is long, the light eventually catches up to the matter from behind. At that point, the matter is in the lead, if we disregard the first cycle.

 

If the number of frequency cycles is held constant, because the composite distance has gotten smaller than the incident wave, the composite wave will not be able to leave the medium. Theoretically, it would look like the light stops short of reaching the other side, suspended in the medium. This may be indicative of medium transparency changing to translucency. In some cases the translucency theoretically changes to reflectivity.

 

Instead of looking at a stop in time, if this is a dynamic system where the light continues to pass, lag, catch up and overtake the matter, again and again, the results would be the composite wave constantly changing the angle of the refraction, with the medium shifting between various states of transparency and translucency. From the other side of the medium, it would look like the light beam has gotten wider with a dim center. This sort of describes diffraction through a small hole. With the energy constant there are less photons in the center and more in the bend zones. If we place a different medium in the hole, than just air, one could get an energy hole in the center.