Theory of loss measurements of Fabry Perot resonators by Fourier analysis of the transmission spectra

We present a detailed theoretical analysis for the determination of the total internal loss in Fabry–Perot resonators based on Fourier analysis of the emission or transmission spectrum. The observation of higher-order harmonics and their relative height in the Fourier-transformed spectrum allow us to quantify the total resonator loss. Because this new method considers both contrast and shape of the Fabry–Perot fringes it is especially well suited for the evaluation of high-finesse laser resonators such as those of vertical cavity surface-emitting lasers in terms of propagation loss/gain.