Watt-level ultrafast 1.75 μm laser system based on thulium-doped core and terbium-doped cladding fluoride fibers

Abstract We report watt-level femtosecond pulses in the 1.75 μm region using a thulium-doped core, terbium-doped cladding fluoride (Tm:Tb:ZBLAN) fiber laser system. The seed pulse is generated through stimulated Raman scattering in a silica fiber pumped by a femtosecond erbium-doped fiber laser. The soliton is stretched with a chirped fiber Bragg grating (CFBG), and is subsequently amplified through a multi-stage Tm:Tb:ZBLAN amplifier. The amplified pulse is compressed with high temporal quality due to the fine dispersion tuning with the CFBG. The system can generate a maximum of ∼250 nJ of single-pulse energy with an average power of ∼1 W at a repetition rate of 4 MHz. The laser system is suitable for multiphoton microscopy.