Photodiode-based phase-retrieval ultrafast waveform measurements

Summary form only given. Frequency-resolved optical gating (FROG) is becoming a standard method for characterizing the amplitude and phase of ultrashort pulses. In FROG, the optical waveform is calculated from the power spectrum of the autocorrelation signal generated by nonlinear wave mixing. As discussed previously, nonlinear wave mixing has the following disadvantages: (1) To measure sub-50-fs pulses, a crystal as thin as several tens of micrometers is required to avoid dispersion-induced pulse broadening and to ensure a sufficiently broad phase-matching bandwidth. (2) Wave mixing in thin nonlinear crystals is intrinsically an inefficient process. This sets a limit on the sensitivity. We developed a phase-retrieval waveform measurement technique by using only photodiodes. Because the nonlinear signal was obtained from two-photon-induced photocurrent, the above disadvantages were eliminated.