  Amplified spontaneous emission (ASE) causes fluctuations of pulse energy, of
the optical phase and of the timing of the pulse intensity envelope in a
mode-locked laser or frequency comb. Starting from the assumption of one ASE
photon per longitudinal laser mode and roundtrip, we rederive analytic
equations for the three fundamental types of quantum noise in a laser. To this
end, we analyze the interference of the coherent intracavity field and a
spectrally localized ASE photon as a function of wavelength and phase of the
latter. Performing an integration over all wavelengths and phases and taking
stochastic noise into account, we compute ASE-induced jitters for all
quantities considered. Continuing this approach, we then derive an expression
for the resulting carrier-envelope phase noise of the comb, for which so far
only numerical estimates exist. We further compute analytical estimates for ASE
induced pulse chirp and duration variations and address the issue of resulting
pulse contrast in a mode-locked laser and the resulting coherence properties.
Considering three example cases, we finally compute estimates for all
quantities analyzed. Taken together, our analysis provides a comprehensive view
of ASE effects in a mode-locked laser, which unites numerous scattered reports
across the literature.
