Wavelength vs. Frequency Modulation

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Niles
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Hi

I have read a paper, where they distinguish between wavelength and frequency modulation. More specifically:

"FMS (frequency modulation spectroscopy) can be broken down into two regimes: wavelength modulation (WM) and frequency modulation (FM). In the case of WM, the modulation depth is very large, generating a large number of sidebands, but the modulation frequency is low (<1 MHz); in the case of FM, the modulation depth is small but the frequency is very high (>100 MHz)."

I know the math behind phase modulation, so when they say that a large modulation depth leads to many sidebands, I agree with this. But I don't see why the two domains are labelled "WM" and "FM"?


Niles.
 
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