Hi I have read the following online (http://tf.nist.gov/general/pdf/1819.pdf): "Regardless of the application, the basic goal of locking the frequency of a laser to a cavity is to reduce the frequency fluctuations between the laser and cavity. The noise spectrum of the laser’s frequency fluctuations leads to an effective “linewidth” of the laser, which conceptually describes the broadening of the laser’s spectrum around its central frequency". What I don't understand 100% is the bolded part. So what they are trying to tell me is that the noise spectrum of the (e.g.) Lorentzian width of a laser is what makes it Lorentzian? Best, Niles.