Simultaneous measurement of the phase noise on all optical modes of a mode-locked laser

We propose and experimentally demonstrate a method to simultaneously measure the relative phase noise of all modes of two mode-locked lasers. The method is based on the numerical analysis of a beat note of two lasers with slightly different pulse repetition rates. We carefully analyze and experimentally demonstrate the potential of this method. Compared to other methods, it has the unique advantage that it provides access to correlations of the phases of different modes.