High Energy Noise-Like Pulse Generation from a Mode-Locked Thulium-Doped Fiber Laser at 1.7 μm

Thulium-doped fiber laser (TDFL) is a versatile platform that can be engineered to produce laser sources with desired performance that target a vast number of applications, however its operation in the 1.7-μm region is still underdeveloped owing to the quasi-three-level nature of TDF emission. In this paper, we report a high energy noise-like pulse generation from a nonlinear polarization rotation (NPR) mode-locked TDFL. By using highly efficient core-pumping at 1650 nm and intra-cavity filtering component, stable mode-locking operation at 1750 nm is realized at a pump threshold of 1.5 W. With increasing the pump power to 5 W, the pulse width is stretched from 0.8 ns to 3.7 ns, while the monitored output power is linearly increased from 50 mW to 251 mW, corresponding to a maximum pulse energy of 321 nJ at the pulse repetition rate of 782 kHz. The long-term and shot-to-shot stability of the output are characterized to be 0.11 dB and 2.8% respectively. Noise-like pulse operation of the laser is confirmed by measuring the autocorrelation trace, which demonstrates a coherent peak on top of a wide pedestal. To the best of our knowledge, this is the first demonstration of high energy noise-like pulse generation from a TDFL at 1.7-μm band, enabling potential applications in for example spectroscopic analysis and material processing.