Demonstration of kilowatt monolithic Yb-doped fiber laser operation near 980 nm

Demonstration of hundred-watt-level near-diffraction-limited monolithic fiber laser near 980 nm with step-index double-cladding Yb-doped fiber

In this paper, a hundred-watt-level near-diffraction-limited step-index Yb-doped fiber (YDF) laser near 980 nm is demonstrated firstly, to the best of our knowledge. By using the 11.7-W 979-nm single-mode seed light, the in-band amplified spontaneous emission (ASE) is well suppressed and the maximum output power of 101.5 W with the beam quality (M2 factor) of 1.285 was obtained. This work does not only propose an effective method for the suppression of in-band ASE, but also provides a cost-effective solution of hundred-Watt-level near-diffraction-limited fiber lasers near 980 nm.

Requirements on double-cladding Yb-doped fiber for power scaling of diffraction-limited fiber amplifiers

Requirements on the double-cladding Yb-doped fiber (DCYF) for power scaling of diffraction-limited fiber amplifiers are studied in this paper. By considering the limitations of thermal lens and transverse mode instability separately, it is found that the power scaling limit can be enlarged to more-than 100 kW and 80 kW, respectively, with the proper selection of pump and signal wavelengths. It is also found that the requirements on DCYF strongly depend on the wavelength and brightness of pump light. It is predicted that smaller-than 20-µm core diameter is required to achieve the 20-kW output power, as long as the 976-nm pump brightness can be high enough. The requirements on the inner-cladding diameter and cladding-to-core ratio of DCYF are also investigated.

FDTD modeling of excitation-balanced, mJ-level pulse amplifiers in Yb-doped double-clad optical fibers

A finite-difference time-domain (FDTD) simulation of Yb-doped cladding-pumped, mJ-level, excitation-balanced fiber pulse amplifiers (EBFAs) is presented. In EBFAs, two pumps, one above (anti-Stokes pump, or ASP) and one below (Stokes pump, or SP) the signal wavelength, are utilized to reduce the net thermal energy generated due to the quantum defect. From the results of the FDTD simulation, detailed analyses on the fiber length optimization, excited Yb3+ population evolution, pump and signal power evolution, optical-to-optical (o-o) conversion efficiency, wall plug efficiency, as well as thermal energy generation are performed. For example, with an ASP at 990 nm and a SP at 975 nm, only 2.3 µJ of thermal energy is produced when generating a 2 mJ output pulse at 985 nm, whereas a pulse amplifier with only SP pumping rendering the same 2 mJ output gives more than 10 times the thermal energy. In the meantime, the system maintains an o-o efficiency of 8.43% and wall plug efficiency of 6.6%. The results here indicate the feasibility of the power-scaling of excitation-balanced laser systems, and the FDTD model will be beneficial for the design and optimization of such systems. The first half of this paper presents the FDTD model and provides an example calculation outlining the modeling procedure. The remaining half details the impact of varying laser parameters on system performance. These include pumping and input signal energies, repetition rates, and selection of the ASP, SP, and signal wavelengths. The results presented herein can also be extended to excitation balancing in other solid-state laser systems, such as Yb:YAG and Tm:YAG lasers.

Efficient single-frequency 972 nm Yb-doped fiber amplifier with core pumping and elevated temperature

In this work, we present a monolithic single-frequency, single-mode and polarization maintaining Yb-doped fiber (YDF) amplifier delivering up to 6.9 W at 972 nm with a high efficiency of 53.6%. Core pumping at 915 nm and elevated temperature of 300 °C were applied to suppress the unwanted 977 nm and 1030 nm ASE in YDF, so as to improve the 972 nm laser efficiency. In addition, the amplifier was further used to generate a single-frequency 486 nm blue laser with 590 mW of output power by single-pass frequency doubling.

Experimental Study on the In-Band Amplified Spontaneous Emission in the Single-Mode Continuous-Wave Yb-Doped Fiber Amplifier Operating near 980 nm

In this paper, the in-band amplified spontaneous emission (ASE) in the Yb-doped continuous-wave (CW) fiber amplifier operating near 980 nm is experimentally studied for the first time, to the best of our knowledge. A core-pumped single-mode Yb-doped fiber amplifier is fabricated and the effects of pump power, seed power, and active fiber length on the in-band ASE are investigated in the experiment. It is found that a strong in-band ASE around 980 nm can be observed even with no obvious ASE around 1030 nm present. It is also found that with the increment of pump power, the in-band ASE can be enhanced faster than the signal light. By studying the effects of seed power and active fiber length, it is found that, although increasing the seed power and shortening the active fiber can both suppress the in-band ASE, the latter method is less effective than the former one. The theoretical study is also carried out in order to understand the difference between the in-band ASE and 1030-nm ASE. The experimental observations are also discussed qualitatively with the theoretical results. We believe that the pertinent results and discussions can provide significant guidance for understanding the in-band ASE in the Yb-doped fiber amplifier operating near 980 nm.