Hybrid wavelength pumping 2-μm ultrafast fiber chirped pulse amplifier based on spatial spectral modulation

We demonstrate a 2 μm ultrafast fiber chirped-pulse amplifier (FCPA) utilizing dual-wavelength hybrid pumping at 793 nm and 1570 nm. Seeded by a high-power nonlinear polarization rotation oscillator, hybrid pumping improved optical conversion efficiency by 9.4% compared with single-wavelength pumping. Stimulated Raman scattering was observed with a 20-W 793-nm pump but suppressed under 30 W hybrid pumping. A spatial spectral modulator in the pulse stretcher optimized pulse quality. The system delivered 235 fs pulses at 5.2 W up to 11.23-W, 51.6-MHz, 445-fs, 1978-nm, demonstrating an efficient route to high-power 2-μm femtosecond fiber lasers.