Efficient cascade Raman source in methane-filled hollow-core fibers operating at 2.8 um

We report here a novel two-stage approach Raman cascade laser source operating at 2.8 μm. In the first stage, a pulsed pump laser at 1064.6 nm is coupled into a methane-filled hollow-core fiber and efficiently transfer to 1st Stokes wave at 1543.9 nm. The quantum efficiency is ~ 87%, which is achieved in 2 bar methane pressure and 2 m fiber length. In the second stage, the 1st Stokes wave is coupled into another methane-filled hollow-core fiber as the pump source, 2nd Stokes wave at 2.8 μm is obtained with a high quantum efficiency of ~75%, which is achieved in 11 bar methane and 2.2 m fiber length. The record total quantum efficiency (from the 1064 nm pump laser to Stokes wave at 2.8 μm) of ~ 65% is achieved, which is 1.6 times the previous reported value. This kind of gas filled hollow-core cascade Raman laser source provides a potential method to obtain high efficiency mid-infrared laser sources with low threshold in various applications.