All-fiber ultrafast tunable thulium laser at 1.7 µm

We present a fully fiberized, wavelength-tunable ultrafast thulium laser source that combines a mode-locked oscillator and a chirped-pulse amplifier to generate high-peak-power pulses in the 1.7 µm spectral region. The oscillator employs a carbon nanotube saturable absorber and a bending-induced short-pass filter integrated into a dispersion compensation fiber (DCF), enabling simultaneous dispersion management and spectral shaping. By varying the DCF bending radius, continuous wavelength tuning from 1740nm to 1860nm is achieved, with stretched-pulse solitons produced at the short-wavelength end of the tuning range. The seed pulses are amplified in a single-stage thulium-doped fiber amplifier incorporating two bi-directionally pumped gain sections separated by a DCF filter to enhance short-wavelength gain. The system delivers 13.2 nJ pulses compressed to 366 fs, corresponding to peak powers exceeding 36 kW. The demonstrated architecture offers a compact and robust platform for generating tunable, high-power femtosecond pulses at 1.7 µm, making it potential for deep-tissue multiphoton imaging, spectroscopy, and other nonlinear optical applications.