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how should i interpret an article about light being slowed and comprressed?

how should i interpret an article about light being slowed and comprressed?


1 Answers

askIITians Faculty 747 Points
5 years ago
All of the resources you point to are indeed related, and are examples of what is calledslow light. This phenomenon refers to the extraordinarily slow speeds that can be enforced on light pulses when they traverse gas cells that are under the influence of additional light beams.

However, you do not need all that fancy apparatus to make light go slower thanc. Indeed,the speed of light within any normal material mediumwill be slower thancby a factor of the medium's index of refraction. This means that you can use, say, glass, to 'slow and compress' a light pulse, though of course by much, much less than what you've read.

There are multiple ways to understand why this happens, and it is important to stress that they all apply both to the exotic gas-phase experiments and to ordinary glass. I would tend to phrase it in terms of an electromagnetic wave trying to propagate through a region that contains electric charges, which changes the propagation equation.

You can also see it, though, as the absorption and re-emission of photons by the material medium. As the light beam reaches each atom in the medium, there is a small chance that it will be absorbed and re-emitted. The corresponding time delay induces a phase shift between the original and the re-emitted beam, and when the two interfere the result will be a phase shift in the light, if it is monochromatic. To get slow light, you needa medium whose refractive index rises (steeply) with frequency, which means that the higher-frequency components of your pulse accumulate a bigger phase shift than the slower ones. When you add all the phase-shifted components together, the net result is a slower pulse. Thus, there's several 'layers' involved, but it is in the end all down to photons being absorbed and re-emitted after a certain delay.

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