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We report the development of a single-mode picosecond-pulsed thulium-doped fibre laser system operating at 1749 nm with an all-fiberised configuration. A gain-switched laser diode is employed to seed the system, producing 36 ps pulses with a controllable pulse repetition rate. Two custom-designed amplification stages deliver a total gain of 54 dB and a maximum average output power exceeding 3 W. To mitigate signal reabsorption, long-wavelength amplified spontaneous (ASE) is initially filtered using a tailored short-pass filter and further suppressed using an in-house developed thulium-doped fibre optimised for the 1.7 μm spectral region. At a repetition rate rate of 34 MHz the system provides a pulse energy of 88.8 nJ and a peak power of 1.8 kW. Stable operation is maintained across a wide repetition rate range from 34 MHz to 1.5 GHz. To the best of our knowledge, this is the first all-fiberised, multi-Watt, picosecond thulium-doped fibre laser system at 1.7 μm featuring a controllable repetition rate. This system broadens the known capabilities of the short side of the thulium emission band, and is an attractive source for applications in biomedical science and mid-IR laser power scaling.
Gerard et al. (Thu,) studied this question.