Synchronized time lens based temporal magnifier assisted by the phase lock loop.

We propose a synchronized time lens based temporal magnifier for the characterization of an ultrafast pulse, which is assisted by the phase lock loop (PLL) to actively lock the repetition rates of the pump laser and signal laser. A feedback control system combining a proportional-integral (PI) circuit and a piezoelectric transducer (PZT) inside the signal laser cavity is used to synchronize the repetition rates between the pump and signal lights. Benefitting from the PLL technique, the temporal position of the signal pulse remains as the numerical aperture of the time lens system, and therefore it has a high short-time stability for pulse measurement. This synchronized time lens based temporal magnifier can record single-shot pulses within continuous round trips. By engineering the dispersion of the pump, signal, and idler lights, we demonstrate a 200× magnification of the signal pulse. Our technique offers a simple synchronized method in a time lens system for ultrafast temporal characterization, which provides new insights into the observation of the fiber laser dynamics.