We report a compact, tunable, self-starting, all-fiber laser-based asynchronous optical sampling (ASOPS) system. Two Er-doped fiber oscillators were used as the pulsedlaser source, whose repetition rate could be set at 100-MHz with a tuning range of 1.25 MHz through a fiber delay line. By employing phase-locked and temperature control loops, the repetition rate offset of the two lasers was stabilized with 7.13 × 10 −11 fractional instability at an average time of 1 s. Its capabilities in the terahertz regime were demonstrated by terahertz time-domain spectroscopy (THz-TDS), achieving a spectral bandwidth of 3 THz with a dynamic range of 30 dB. The large range of repetition rate adjustment in our ASOPS system has the potential to be a powerful tool in the terahertz regime.

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