To continue the guide star laser work, we have first researched ways to generate linearly polarized Yb doped fiber laser, and are now able to build100 W class linearly polarized 1120 nm Yb-doped fiber laser with cross-axis-matched FBG pairs written in polarization maintaining fiber. We improved the SBS suppression technique further, and achieved a 44 W single frequency Raman fiber amplifier at 1178 nm with an optical efficiency of 52 %. Up to 25 W at 589 nm has been demonstrated with a home-built frequency doubling cavity, which is not yet optimized.
Mode locking of fiber laser is another fascinating field we are interested. We studied mode locking of Raman fiber laser with graphene absorber. The idea is simple: To achieve wavelength versatile mode locked fiber laser by combining the shared advantage of Raman gain and graphene saturable absorption, both of which is broadband. During the path, we have demonstrated passively Q-switched Yb-doped fiber laser by graphene, and the use of single-multi-single mode fiber structure as bandpass filter for building all fiber tunable dissipative soliton fiber laser.
The SBS suppression technique was applied to single frequency Yb doped fiber laser, and achieved 170 W linearly polarized laser with a 10 micron core PM fiber by 7 time increase of SBS threshold. We also find Yb doped fiber laser at the wing of gain spectrum interesting. One example is a demonstration of high power single frequency 1014.8 nm fiber amplifier working at room temperature for mercury cooling after frequency quadruplication. These works are not yet published.