Coherence characterization of nanosecond rectangular pulses in passively mode-locked fiber lasers

Dissipative soliton resonance (DSR) phenomenon is a recent concept of pulse formation proposed to achieve a high-energy passively mode-locked fiber laser. Such pulses have general features, e.g., flat-top temporal profile, energy scalability, and temporal coherence. To identify the nature of various rectangular pulses which share most of DSR features, it is important to verify their coherence. When a pulse is in the nanosecond range, the experimental study of the coherence is a complex task, which is overlooked in the literature. In this work, a novel approach is proposed for the first time to study the coherence of nanosecond rectangular pulses. It is based on two different methods: Mach-Zehnder interferometer (MZI) and dispersive Fourier transformation (DFT).