[lyner]

I think you would need a material with a negative coefficient of dispersion, though.

[lightarrow]

I think you would need a material with a negative coefficient of dispersion, though.

Yes, that was part of "the right material". Note however that you have to choose the material if you have already fixed the frequencies, but you don't need to do it if you don't fix them: any material have a negative slope part of the dispersion curve, exactly from the other side of the positive one, with respect to the absorbtion frequency:
http://phys.strath.ac.uk/12-370/sld081.htm
So, you can take glass, identify a frequency of absorption (with coloured glass this frequency is in the visible) and then choose the two frequencies on the part of the curve where the dispersion coefficient is negative.
Simpler than what we could think, isnt'it?

[yor_on]

"On the other hand, if a photon has an energy beyond the phonon spectrum, then while it can still cause a disturbance of the lattice ions, the solid cannot sustain this vibration, because the phonon mode isn't available. This is similar to trying to oscillate something at a different frequency than the resonance frequency.

So the lattice does not absorb this photon and it is re-emitted but with a very slight delay.

This, naively, is the origin of the apparent slowdown of the light speed in the material. The emitted photon may encounter other lattice ions as it makes its way through the material and this accumulate the delay."

How exactly is this photon 'delayed'?

It will move at 'c' in 'any space' and there is a lot of space available in atoms no matter what matter.
In a BEC you slow photons by pushing it in the direction it came from,
Is it this that means, or is like getting through some sort of 'density' created by the electron clouds.
That is, if we look at photons particle wise.

[lyner]

I think you would need a material with a negative coefficient of dispersion, though.

Yes, that was part of "the right material". Note however that you have to choose the material if you have already fixed the frequencies, but you don't need to do it if you don't fix them: any material have a negative slope part of the dispersion curve, exactly from the other side of the positive one, with respect to the absorbtion frequency:
http://phys.strath.ac.uk/12-370/sld081.htm
So, you can take glass, identify a frequency of absorption (with coloured glass this frequency is in the visible) and then choose the two frequencies on the part of the curve where the dispersion coefficient is negative.
Simpler than what we could think, isnt'it?

I have an idea that the graph in the link refers to the classical group delay characteristic of a minimum phase bandpass filter (digging back in my memory). Does it still apply to a piece of coloured glass?
I think that 'coloured glass' - if you just mean pigmented glass - wouldn't do the same job. The bulk of the medium would still be the basic glass so would the total phase shift be due to a combination of the two materials? It's not just a simple resonator.

[Bored chemist]

As the moon is moving towards/away from earth, a light from earth would show a nanosecond blue/red shift. This is due to Doppler effect. Agree?

If you are on the Moon observing a light beam from Earth, you will see it blue shifted if the Moon approaches Earth and red shifted if the Moon recedes from Earth.

But the effect is tiny.

Ah, but it depends on what he intended with "if the Moon approaches Earth"; if he intended "during the actual phase of Moon's approachement to Earth" or if he could mean "in a Moon launched at relativistic speed towards the Earth" (because I haven't understood it) [].
Anyway, the effect is perfectly detectable with modern interferometry (even with no relativistic Moon  []).

Which effect is measurable?
The movement of the moon- (which is fairly small, but fairly easilly measurable) or the doppler shift that this tiny movement produces (which I'm pretty sure would get swamped by the variable effect of the earth's atmosphere?

Incidentally, if you are prepared to take a rather wide interpretation of the word "prism" then dichroic filters and transmit and reflect just about any colours you want.

[lyner]

I am sure that an interference filter could achieve any phase characteristic you wanted, in principle, BC. But, to achieve the same sort of delay characteristic corresponding to the TIME dispersion in a prism, you would need a lot of layers, I think.

[lightarrow]

I have an idea that the graph in the link refers to the classical group delay characteristic of a minimum phase bandpass filter (digging back in my memory). Does it still apply to a piece of coloured glass?
I think that 'coloured glass' - if you just mean pigmented glass - wouldn't do the same job. The bulk of the medium would still be the basic glass so would the total phase shift be due to a combination of the two materials? It's not just a simple resonator.

From the book "Fundamentals of Optics" - Jenkins/White - fourth edition - paragraph 23.4 "Anomalous dispersion":

...
The existence of a large discontinuity in the dispersion curve as it crosses an absorption band gives rise to anomalous dispersion. The dispersion is anomalous because in his neighborhood the longer wavelenghts have a higher value of n and are more refracted than the shorter ones. The phenomenon was discovered with certain substances, such as the red fuchsin and iodine vapor, whose absorption bands fall in the visible region. A prism formed of such a substance will deviate the red rays more than the violet, giving a spectrum which is very different from that formed by a substance having normal dispersion. When it was later discovered that transparent substances like glass and quartz possess regions of selective absorption in the infrared and ultraviolet, and therefore show anomalous dispersion in these regions, the term "anomalous" was seen to be inappropriate. No substance exist which  does not have selective absorption at same wavelenghts, and hence the phenomen, far from being anomalous, is perfectly general. The so-called normal dispersion is found only when we observe those wavelenghts which lie between two absorption bands, and fairly far removed from them.

[labview1958 (OP)]

When light passes in air it is in "deep" space compared to when it passes through glass, it is in "shallow" space. Thus the light bends giving rise to the refractive index. Thus deep/shallow space depends on the medium.