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High power 780 nm laser for quantum science and technology

Diffraction-limited single frequency 780 nm lasers are required to cool and manipulate rubidium atoms for various quantum applications. For advanced quantum technology applications like large scale atom interferometers, high power (several tens watts and more) 780 nm laser is required. Several effords had been reported to produce over ten watts 780 nm laser by frequency doubling of a 1560 nm Er fiber amplifier.

We have made our contribution recently based on our knowledge in high power Raman fiber laser and high efficiency freqeuncy doubling. A home-made a high power 1480 nm Raman fiber laser is used it to core-pump a Er fiber amplifier directly into the up level of the laser transition. It allows high power and high efficiency amplification of the 1560 nm single frequency laser before the onset of stimulated Brillouin scattering. With the 50 W 1560 nm output, a 21.2 W continuous-wave single frequency 780 nm laser was achieved by utilizing single-pass frequency doubling in a MgO:PPLN crystal.

The result is reported recently on Optics Letters.
J. Dong, X. Zeng, S. Cui, J. Zhou, and Y. Feng, “More than 20 W fiber-based continuous-wave single frequency laser at 780 nm,” Opt. Express 27(24), 35362 (2019).

The work is an excellent demonstration of our combined experience on high power Raman fiber lasers, high power single frequency fiber amplifiers, and high efficiency second harmonic generation.

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In the past five years…

It is already five years that I blogged nothing here. Just give a short outlines here to show the main research achievements.

We have improved and maturized the Raman fiber amplifier based guide star lasers. The laser can now operate at CW, 100 microsecond quasi-CW, and pulsed at Larmor frequency. Laser prototypes were tested at telescopes for sodium guide star, and also for mesospheric magnetometry.

With cascaded random Raman fiber laser, we have demonstrated up to 11 th Raman Stokes light generation. With a Yb pump laser at 1 micron, continuous wavelength tuning up to 2 micron were demonstrated. With this technology, fiber lasers can now output more than 100 W at any wavelength from 1030 nm to 2000 nm.

We continued our study on mode locked Raman fiber lasers, have made some interesting demonstrations including NPR mode locked dissipative soliton, figure of 8 dissipative soliton, rectangular pulse generation etc. We believe we have improved the understanding of mode locked Raman fiber lasers now.

Amplified spontanesou emission sources were found to be useful for pumping cascaded random Raman fiber lasers and mode locked Raman fiber lasers.

Specialty lasers at various wavelengths were demonstrated with wavelength tuning of fiber lasers and second harmonic generations.

Besides, we have made contributions in scattered topics. Many of them are actually more interesting and look for futher developments. Check out our publication list.

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Raman fiber laser goes to kilowatt level

Using the integrated Ytterbium-Raman fiber amplifier architecture, we are now able to generate over kilowatt Raman fiber laser.

A kilowatt-level Raman fiber laser is demonstrated with an integrated Ytterbium-Raman fiber amplifier architecture. A high power Ytterbium-doped fiber master oscillator power amplifier at 1080 nm is seeded with a 1120 nm fiber laser at the same time. By this way, a kilowatt-level Raman pump laser at 1080 nm and signal laser at 1120 nm is combined in the fiber core. The subsequent power conversion from 1080 nm to 1120 nm is accomplished in a 70 m long passive fiber. A 1.28 kW all-fiber Raman amplifier at 1120 nm with an optical efficiency of 70% is demonstrated, limited only by the available pump power. To the best of our knowledge, this is the first report of Raman fiber laser with over one kilowatt output.

The work is published recently on Optics Express: L. Zhang, C. Liu, H. Jiang, Y. Qi, B. He, J. Zhou, X. Gu, and Y. Feng, “Kilowatt Ytterbium-Raman fiber laser,” Opt. Express 22, 18483 (2014).

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Integrated ytterbium-Raman fiber amplifier

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.

Lei Zhang, Huawei Jiang, Shuzhen Cui, and Yan Feng, “Integrated ytterbium-Raman fiber amplifier,” Opt. Lett. 39, 1933-1936 (2014) .

update: The work is reported  in the may issue of Laser Focus World.

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Update in 2013

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.

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A short summary of what we have done in 2012

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.