High-Energy 1.96–2.4 μm Tunable Raman Soliton Generation in All-Silica-Fiber Tm-Doped Amplifier

Femtosecond pulses in the 2- $2.4\mu \text{m}$ spectral region have potential applications in many fields, such as two-photon fluorescence imaging, sensitive molecular spectroscopy, and nonlinear laser system. As the energy is proportional to the square of the soliton order, the high-energy soliton pulse can be achieved by promoting the soliton order during the soliton splitting and soliton self-frequency shifting processes. We demonstrated high-energy Raman solitons with wavelengths tunable from 1.96 to $2.39\mu \text{m}$ in a thulium-doped silica fiber amplifier. The maximum pulse energy of the soliton was about 65.1-nJ with the corresponding wavelength of $2.39\mu \text{m}$ , which, to our knowledge, was the farthest and the highest energy soliton pulse generated in commercial single-mode silica fiber.