High average power pulsed multi-mode Raman fiber laser in graded index fiber

Abstract

Raman fiber lasers have seen increased interest recently, due to their ability to access difficult wavelength ranges without the use of specially doped materials and to avoid some of the obstacles of very high power rare-earth doped fiber lasers, including modal instability and photodarkening. Though most modern works in Raman fiber lasers are based on fiber laser or direct diode pumping, solid state lasers have been developed with extremely high average powers and are readily available commercially. This work explores a very short fiber length high average power multi-mode Raman laser system. The custom 200um graded index fiber is pumped by 30ns pulses with average powers up to 750W and pulse energies up to 7.5mJ at 1030nm, by a solid state commercial laser system. Pump-only and seeded configurations are examined. In the seeded case, higher order mode activation is demonstrated by detuning the single mode seed to preferentially feed energy to the less confined modes. 5 orders of Stokes are demonstrated, ranging from 1078nm to 1350 nm. Beam enhancement is observed by qualitative measurement of minimum beam waist, and average powers up to 70W are achieved at an energy of 1.4mJ.