High-efficiency femtosecond Raman soliton generation with a tunable wavelength beyond 2 μm.

We report an efficient Raman soliton laser system by optimizing the chirp of input pulses. The highest efficiency of energy transferred to a Raman soliton is up to 97%, and the tunable range is from 1.98 to 2.31 μm. The pulse width of these tunable Raman solitons remains below 200 fs. The efficiency and the wavelength range are mainly limited by the background loss of the silica fiber.