# Tag Info

14

Very reasonable question. I will try to answer it in an intuitive way. If you have a scattering medium, photons are reflected in random directions; but when you have a refractive medium, something else happens. The photon is not absorbed and re-emitted: instead, the photon interacts with the electrons in the medium, and since these electrons are somewhat ...

4

The point-source response is also called the point-spread function (at least for telescopes). This defines how an idealized dot of light at infinity is imaged by the optics of the telescope (or eye). Instead of appearing as a perfect dot (presumably on a single pixel, assuming sufficiently small pixels, for a camera), the dot is imaged as some complicated ...

2

That's right. There are materials that possess these properties. They are birefringent, see Wiki Page Birefringence. Crystals can have different refractive indices along their crystal axes which leads to the phenomenon that you describe.

2

The light is reflected from a mirror. If the mirror moves a distance $\frac \lambda 2$ then the incident ray of light has to travel an extra distance $\frac \lambda 2$ to reach the mirror and then the reflected ray of light has to move an extra $\frac \lambda 2$ a total extra distance of $\lambda$. If the path length changes by one wavelength then there is ...

1

If you have access to some physics review, I suggest you look at a series of articles by Anthony A. Tovar and Lee W. Casperson, "Generalized beam matrices: Gaussian beam propagation in misaligned complex optical systems," J. Opt. Soc. Am. A 12, 1522-1533 (1995) in which they describe the ABCDGH transfer matrix formalism. Here is the link to the first one on ...

1

Just to add to the above answers, and since to did not limit your question to the visible range - if you define black as absence of light (photons emitted or reflected), then there is no such substance, because according to black body radiation model, everything with a temperature above absolute zero (which is essentially truly everything in the universe:) ...

1

Semiconductor light emitters are made of such materials, which have quite large index of refraction. This makes it hard for light to exit the emitter — due to Fresnel equations and low index of refraction of air. In a laser the light mostly goes back and forth between two mirrors, and reflections only help the lasing. So the light either exits from a tiny ...

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