greypilgrim
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- TL;DR Summary
- Why do sine-like waves travel at constant speed in a dispersive medium, and not for example triangle waves?
Hi.
Light travelling in dispersive media is normally treated by being broken up into its harmonic constituents by Fourier analysis and those then travel at frequency-dependent, but constant speed.
However, from a mathematical point of view, there should be infinitely many other bases of the vector space of periodic functions that are not sine-like, and there is no mathematical reason why the sines should be preferred. For example, the Walsh basis consists of square waves (but there surely are also bases with smooth periodic functions).
So why is it that exactly the sine-like waves travel at constant speed?
My guess is that it comes down to the single oscillators of the medium and that they are treated as harmonic in first-order approximation, which then distinguishes sines from other bases. Does that work?
Light travelling in dispersive media is normally treated by being broken up into its harmonic constituents by Fourier analysis and those then travel at frequency-dependent, but constant speed.
However, from a mathematical point of view, there should be infinitely many other bases of the vector space of periodic functions that are not sine-like, and there is no mathematical reason why the sines should be preferred. For example, the Walsh basis consists of square waves (but there surely are also bases with smooth periodic functions).
So why is it that exactly the sine-like waves travel at constant speed?
My guess is that it comes down to the single oscillators of the medium and that they are treated as harmonic in first-order approximation, which then distinguishes sines from other bases. Does that work?