Femtosecond Laser Pulse Picking Method Based on Mach–Zehnder Modulator by Keeping Phase of the Picked-Up Pulse Steady

In the femtosecond laser pulse picking based on the Mach–Zehnder modulator (MZM), the operating point drift of MZM and the timing mismatch between the impulse gate signal and the laser pulse limit the performance of picked-up pulses. In this article, an adaptive femtosecond laser pulse picking scheme by keeping the phase of the picked-up pulse steady is proposed. For the first time, we have established a one-to-one correspondence between the phase of the picked-up pulse and the operating point of MZM. Therefore, the operating point of MZM can be locked at the null point by maintaining the phase of the pick-up pulses at the value corresponding to the initial null point with the closed-loop bias control. By maximizing the amplitude of the picked-up pulses, the automatic matching of the impulse gate signal and the laser pulses can be realized. The principle and realization of the impulse signal generation and bias control are presented in detail. Experimental results verify that the proposed method has achieved flexible single/multiple pulse-picking with repetition rates from kHz to tens of MHz with high amplitude stability, high extinction ratio, and low temporal broadening and profile distortion.