Simple amplitude and phase measuring technique for ultrahigh-repetition-rate lasers

A simple method for the full amplitude and phase characterization of the light emitted by continuous-wave ultrahigh-repetition-rate lasers is experimentally demonstrated. The method is based on the measurement of the beat notes obtained by filtering pairs of adjacent longitudinal laser modes in a high-resolution, zero-dispersion grating-lens spectroscope arrangement. The method only requires the use of a simple fast photodiode and does not involve any nonlinear optical process.