The Institute of Applied Physics of the Russian Academy of Sciences named after A.V. Gaponov-Grekhov has proposed an innovative concept for a rod-shaped ytterbium amplifier of a diverging beam, which provides both high peak and average radiation power. This development can seriously compete with the slab and disk lasers prevailing on the market due to its simplicity and efficiency.
The concept of a rod-shaped ytterbium amplifier developed at the Institute of Applied Physics of the Russian Academy of Sciences offers a solution for achieving high average power and large pulse energy. It is based on the use of a rod-shaped active element in the form of a truncated cone, where the pump and laser radiation propagates from the smaller end to the larger one, which leads to an increase in the size of the beams as they propagate.
In the narrow part of the rod, effective signal amplification is carried out due to the high pump intensity and good cooling. The wide part of the rod is designed to extract high-energy pulses without the risk of breakdown of the output end.
The key problem we faced in implementing this concept was the factors that prevent the beam size from increasing during amplification, including the thermal lens, the transverse inhomogeneity of the gain coefficient, and nonlinear self-focusing. Calculations have shown that to compensate for the influence of these factors, it is necessary to significantly increase the initial divergence of the amplified beam. At the same time, the only possible way to achieve the required divergence is to give the input end of the active element a concave spherical shape, which began to play the role of a diverging lens.
Thanks to the application of this concept, it was possible to increase the output pulse energy by a factor of three, while maintaining high average power, amplification efficiency, and beam quality. The achieved parameters are currently record-breaking for rod-shaped ytterbium lasers, and further optimization will improve them.
This work will significantly expand the capabilities of rod-shaped ytterbium lasers, which will allow them to seriously compete with the dominant slab and disk lasers on the market, due to their simplicity and efficiency.
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