Simultaneous measurement of the Lorentzian and Gaussian linewidths of laser

Linewidth is a key parameter reflecting the coherence of single-frequency lasers. While the linewidth contributed by white noise has been widely studied, the effect of nonwhite noise, mainly flicker noise, is hard to evaluate. However, flicker noise can cause linewidth broadening much larger than the Lorentzian component. Considering that interference visibility can serve as an effective indicator of phase noise magnitude, in this work, we quantify flicker noise as Gaussian linewidth and analyze the relation between interference visibility and laser linewidth. We find that the logarithm of visibility depends quadratically on the delay: the linear term is due to white noise, and the quadratic term arises from flicker noise. Based on this finding, we propose a method to simultaneously measure Lorentzian and Gaussian linewidths. This approach not only avoids flicker noise interference in Lorentzian linewidth measurements but also provides a convenient way to assess the magnitude of flicker noise. In addition, this approach effectively reduces the dependence of the linewidth measurement experiment on the length of the delay fiber, with shorter fibers helping to minimize environmental disturbances. More importantly, the introduction of the Gaussian linewidth provides a more comprehensive characterization of the laser linewidth.