Picosecond Raman fibre laser with a wavelength of 2.84 μm

We study SRS generation at a wavelength of 2.84 μm in a hollow-core revolver fibre filled with methane as a function of gas pressure as well as energy and duration of chirped pulses from an erbium-doped fibre source at 1.56 μm. It is shown that the threshold pump pulse energy decreases with increasing methane pressure, while an increase in the pulse width ensures more efficient conversion from 1.56 to 2.84 μm. A maximum pulse energy at 2.84 μm and corresponding quantum conversion efficiency are 1.6 μJ and 12%, respectively. A possibility of conversion efficiency enhancement is demonstrated numerically up to a 50% level under single-mode pumping at a pulse energy up to 100 μJ. It is found numerically that the main process limiting SRS conversion efficiency over the domain of investigated parameters is coherent four-wave mixing.