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Wavelength to frequency

  1. Jan 24, 2012 #1

    Say I have an energy level centered around λ with some linewidth Δλ, and I wish to find the corresponding frequency linewidth Δν. What I would use is the following relation

    Δλ/λ = Δν/ν.

    Is this correct?

    Thanks in advance.

  2. jcsd
  3. Jan 24, 2012 #2


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    Homework Helper

    Yes. It amounts to saying the % error in wavelength is the same as the % error in frequency. This is true because c = f*λ, λ = c/f. No error in c, % errors add when multiplying or dividing.
  4. Jan 24, 2012 #3
    Thanks! If I have a resonator with length e.g. L=3 micron, then the resonances are separated by (the Free Spectral Range c/2L) 50 THz. If I want to find the corresponding separation in wavelength, then how would I do that? I can't use my equation in the previous post, since that is associated with an error.