3 × 1 fiber signal combiner with high beam quality Gaussian-like beam for a 10kW-level fiber laser.

We present the design and fabrication of a 3 × 1 signal combiner with high beam quality based on supermode theory. For improving beam quality, the fiber with core diameter of 34 µm and numerical aperture of 0.11 is first chosen as the output fiber. An 8.89 kW output laser with a power transmission efficiency of 97.2% and a low temperature rise coefficient of 3.5 °C/ kW at >8 kW is obtained when the combiner launched by three Yb-doped fiber lasers. In addition, the energy density distribution of the output beam is Gaussian-like and M2 factor is 2.32, which is the best beam quality compared with the presented signal combiners for high power laser to the best of our knowledge.

All-fiber pulsed laser generation of 25.5 mJ and solution of parasitic oscillation.

A Q-switched, high-energy pulsed master oscillator power amplifier fiber laser utilizing the lab-built 100/400 µm double-cladding Yb-doped fiber is demonstrated. After two-stage amplification, the pulse energy was boosted to 25.5 mJ, for an average power of 510 W at a repetition of 20 kHz, yielding a slope efficiency of approximately 72.8%; the pulse duration was approximately 140 ns, and corresponding peak power was 182.1 kW. What is more, the limitation of further promotion of pulse energy was proposed: the threshold-like parasitic oscillation, which was determined by the injecting power, repetition, and fiber length, was the main restriction on power scaling in ultra-high-energy systems. Efficient solutions were proposed to suppress the parasitic oscillation by experimentally studies.

Yb3+ heavily doped photonic crystal fiber lasers prepared by the glass phase-separation technology.

We report a Yb3+ heavily doped photonic crystal fiber with 30 µm core diameter manufactured for the first time by an alternative technique. Silica core rods with a diameter of 3 mm and a length of 280 mm were prepared by the sodium-borosilicate glass phase-separation technology. The measurements show that the fiber has an Yb3+ concentration of 22810 ppm by weight, and a resultant absorption of approximately 8.5 dB/m at 976 nm. The Yb3+ ions are distributed throughout the fiber core with an excellent homogeneity. The laser performance demonstrates a high slope efficiency of 64.5% for laser emission at 1033.4 nm and a low power threshold of 3 W within a short fiber length of 1 m. This novel approach provides an alternative means of preparing large active silica rods with high doping levels and excellent material homogeneity for large mode area fibers with complex designs.