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Assuming an ideal single frequency plane wave, we can determine the angle of retraction for the light beam.

But the more I make my pulse shorter, the less certain I am in the frequency and thus the angle of refraction, angle of total reflection and Brewsters angle.

Is this true?

If i target a pulsating laser on the glas prism and observe the leaser dot on the wall (in slow motion) does that mean that the angle of refraction will be different for each individual pulse or that the the whole pulse will be more spreadout?

In other words, would the laser dot on the wall dance around randomly or just be much more spreadout compared to a CW?

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  • $\begingroup$ "Retraction". Do you mean "reflection"? $\endgroup$ – my2cts May 21 at 23:20
  • $\begingroup$ I ment refraction. $\endgroup$ – KrNeki May 22 at 7:51
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I assume you are referring to the fact that the refractive index depends on wavelength (this is called dispersion). The answer is that the spot would spread out, with different wavelengths going in different directions.

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  • $\begingroup$ It seems very unintitive to me, that I will spreading out the dot on the wall behind the prism just by waving my hand in front of a laser (creating pulses) and i want a confirmation that that is true? If my medium is extremely dispersive (assuming it exists) and my hand is very fast, i can make the dot spread quite significantly as well as see different colours on the wall although my laser is monochromatic? $\endgroup$ – KrNeki May 22 at 7:31
  • $\begingroup$ Yes, by interrupting the time beam in time you are also changing its frequency components, and hence the way it interacts with a dispersive medium. $\endgroup$ – Andrew Steane May 22 at 8:17
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Snell's law is always valid for a translation invarant interface. A short pulse contains many frequencies and a narrow pulse many directions. This can be considered uncetainty. As materials are usually dispersive, refraction will change the pulse shape.

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  • $\begingroup$ Does that mean that if a laser has a wavelength of 632.8nm, just by waving my hand in front of it (say theoretically with 1 THz), I will be changing its colour? $\endgroup$ – KrNeki May 22 at 7:49

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