Analytic random-walk model for the coherence of a frequency comb

We present an analytical study of the frequency comb coherence due to random noise in the pulses phases. We derive a simple expression for the comb lineshape, which depends on a single parameter Neff with the physical meaning of number of coherent comb pulses, inversely proportional to the variance of the phase jumps between subsequentcombpulses.Acomparisontothecaseofacw-monomode laserwithwhitenoisefrequency fluctuations is also presented.