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In this paper, we present an experimental comparison of coherent beam combining (CBC) effect with different truncation factors based on a triangle fiber laser array for the first time to our best knowledge. First, we fabricate a triangle fiber laser array based on adaptive fiber optics collimators with the fixed focusing length of 0.18m and clear aperture of 50mm. Two output fiber arrays (6/125 fiber array and 20/400 fiber array) with different numerical apertures (0.12 and 0.065, respectively) are used to generate different truncation factors. The direct measurement method is used to measure the intensity distribution of the two collimated beams with different sizes. Results show that the beam diameters are 14.5mm and 27.6mm for 20/400 output fiber and 6/125 output fiber, separately. This means that two fiber laser arrays with truncation factors of 0.29 and 0.55 are achieved. Then we numerically calculate the CBC efficiencies of two situations with different truncation factors. The analytical results show that the CBC efficiency improves from 0.144 with truncation factor of 0.29 to 0.413 with truncation factor of 0.55. At last, a CBC experiment platform is set up. Throughout the whole experiment, single frequency dithering algorithm and SPGD algorithm are separately used to perform the phase-locking control and the tilt control. Two CBC experiments of triangle fiber laser arrays are achieved successfully both with residual phase errors about λ/15. By analysis the experimental results, we get the CBC efficiencies are 0.099 (69% of 0.144) and 0.264 (64% of 0.413) for the two fiber arrays. The experimental results identify the importance of truncation factor on CBC efficiency and provide an important reference on the selection of fiber array parameters in order to achieve the largest energy proportion in the central lobe.
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