Intracavity Phase Modulation and Envelope Phase Noise Transfer in Modelocked Lasers

We derive an expression which relates harmonic intracavity phase modulation to the resulting timing stability degradation of modelocked lasers. Random intracavity phase perturbations can be caused by, e.g., pump power fluctuations, which have been shown to be a significant cause of pulse-to-pulse timing jitter. The noise transfer function describes this frequency-dependent sensitivity of timing stability to pump fluctuations, and we show that it scales as the square of the axial-mode spacing and inversely with the perturbation frequency which together operate as coefficients on the frequency dependence of the cavity photon number, the population inversion, and the gain medium temperature.