The former reports of coherent beam combining (CBC) in the ultra-intense ultra-short laser field focus on the phase control technology and two-beam CBC. To study the four-beam tiled-aperture CBC in the ultra-intense and ultra-short laser field, we demonstrate four-beam CBC of femtosecond laser pulses based on chirped pulse amplification (CPA) scheme. In this experiment, the four beams were compressed using two grating compressors to simulate the situation in ultra-intense and ultra-short laser CBC systems. To achieve real-time measurement of the phase error between the four beams, we introduced a continuous reference laser and the phases of beams 2, 3, and 4 were locked to beam 1.A combined efficiency of 57% was achieved. Although the coherent combining efficiency is not very high, the possibility of a fourbeam CBC based on the CPA scheme was confirmed, especially with different grating compressors which can reduce the limitation of gratings in single beam petawatt lasers. Finally, the remaining difficulties in the implementation of CBC of four beams and the methods to improve its efficiency were analyzed. The use of CBC in ultra-intense and ultrashort laser systems is of considerable significance.

We present and experimentally verify a deep learning approach to synchronously measure the multi-beam pointing error for coherent beam combining systems. This approach uses only one detector by acquiring the far-field interference focal spot, which can greatly reduce the complexity in coherent beam combining systems with high accuracy. The amplitude modulation is utilized to eliminate the confusion of the label values in symmetric system. The position assist camera is used to acquire accurate label value, which solves the mismatch between sample and label value caused by ambient vibration in long-term data acquisition. In simulation and experiment, the RMS accuracy is about 0.3 and 0.5 μrad, respectively, which can greatly meet the pointing measurement requirement in coherent beam combining systems. The result shows that this approach can be well applied to multi-beam coherent combination for high-power laser systems.

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