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It is indeed possible. This was a famous experiment by Isaac Newton (published in 1672). Place a lens of focal length $f$ a distance $2f$ from the first prism. Add a second identical prism $2f$ past the lens and rotate it round until white light emerges. The lens is required to bring the rays back together. It creates an image of the exit of prism one on ...

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Dispersion can be locally nought and effectively nought over quite wide bands in engineered devices. In an optical fiber, for example, the phase delays of the modal fields depends on two things: The dispersion of the material making up the fiber and The frequency dependence of the modal eigenvalue equation, which depends on the refractive index profile ...

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Vacuum with EM field present is also dispersion-less, since EM fields of different sources do not interact directly. So if you pass an EM wave through charged capacitor, the only influence on the wave is due to the matter of capacitor; no influence due to electrified space should occur.

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are there things called infrared photons, or ultraviolet photons etc, as there are infrared waves, or ultraviolet waves? Yes, absolutely. Certain aspects of the photon notion can be thought of as even more like a classical wave than even the above. One photon alone can be in a pure quantum superposition of energy eigenstates, or polarization ...

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As mentioned by others so far, the index of refraction ($n$) of air is not identically equal to 1, but is in fact $n=1.000293$. For many every day situations this small difference is negligible; however, it is possible to observe that light does in fact change speed when changing mediums from a vacuum to air. At sunrise and sunset, the sky appears red ...

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You have two different concepts intertwined in your question. You begin by asking about the speed of light in a medium varying with color (i.e. wavelength). This phenomenon is called dispersion and it is present in all materials including air. Dispersion shows up in many places in the field of optics, but the case you are probably most familiar with is ...

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It is true in general that the speed of light in a medium will depend to some extent on the wavelength/frequency of the light itself, but in most (not all) everyday situations this is not apparent or important, and makes the theory of optics much easier mathematically. As for the refractive index of air, it is not quite 1, but slightly larger, 1.0003 IIRC, ...

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A monochromator, by definition, must separate the light into different wavelength beams. Mirrors are only weakly wavelengthdependent, although some very sophisticated optical dielectric multilayers mirrors can have frequency dependence. Even so, the wavelength dependence of even a multilayer on direction is too weak for this application Gratings on the ...

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