Yesterday, they passed their thesis defenses for Ph.D. and master degree respectively.
An integrated ytterbium-Raman fiber amplifier architecture is proposed for power scaling of a Raman fiber laser. It is an ytterbium (Yb) fiber amplifier seeded with a double or multiple wavelength laser and followed by a passive Raman fiber. A proof of principle experiment demonstrates a 300 W all-fiber linearly polarized single mode amplifier at 1120 nm with an optical efficiency of 70%, limited only by available pump power.
update: The work is reported in the may issue of Laser Focus World.
In 2013, we continued our studies on Raman fiber laser/amplifier and mode locked fiber laser, and development of lasers for guide star and cold atom physics.
We found a method for power scaling of single mode linearly polarized Raman fiber laser. In a proof of principle experiment, an output power of 300 W has been achieved, limited by available power. In the single frequency Raman fiber amplifier direction, we have achieved more than 80 W at 1178 nm in the CW case and more than 120 W in the QCW long pulse case. Consequently, after frequency doubling, more than 50 W CW and 80 W QCW (peak power) laser at 589 nm have been demonstrated. With these results, we are confident that power scaling of Raman fiber amplifier based guide star laser to over 100 W is feasible.
We are always interested in applying our expertise in wavelength flexible high power narrow linewidth fiber amplifier to atomic physics. In this year, we have scale the room temperature 1014.8 nm single frequency fiber amplifier to ~ 20 W, and carried out the frequency doubling and quadrupling experiment to 253.7 nm, and absorption and Doppler-free absorption spectral measurement of mercury atoms.
Together with Prof. Gu of Ryerson University, we also studied mode locked Yb fiber lasers with chirped FBGs, and demonstrated dual wavelength switchable dissipative soliton fiber laser and studied the effect of large normal and anomalous dispersion.
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.
Welcome and stay tuned!