利用准单色光干涉理论, 计算了2×2平顶高斯超短脉冲激光在远场的干涉图样, 分析了激光的时间部分相干性及其存在束间相位差时对相干合成的影响。计算结果表明, 当单路激光输出光束线宽小于100 nm时, 理想波前的远场光斑图样和峰值光强基本保持不变, 当光束线宽大于100 nm时, 干涉减弱衍射效应逐渐增强; 光束间存在相位差时, 时间部分相干性将破坏远场图样随束间相位差的周期性变化, 相位差越大干涉越弱; 当超过相干长度时, 则为非相干合成, 但1/6倍相干长度范围内,仍可视为较理想的相干合成, 此时焦斑的斯特列尔比大于0.9, 对超短脉冲的相干合成影响可忽略。

Using quasi-monochromatic light interference theory, the far-field interference pattern is calculated for the combination of 2×2 flat-topped Gauss ultrashort-pulse lasers, and the effect of phase difference(PD) and temporal partial coherence on coherent combination is discussed. The results show that when the line-width of the beams is less than 100 nm, the far-field pattern and peak light intensity hardly change for ideal wavefront; when the line-width is more than 100 nm, the interference effect weakens gradually. With phase difference, the periodic variation of far-field pattern will be destroyed by temporal partial coherence, and the interference effect gradually becomes weak as the increment of PD. Incoherent combination appears for PD beyond coherent length, while the combination can still be viewed as coherent for PD within 1/6 times the coherent length, when the Strehl ratio is more than 0.9, the effect of temporal partial coherence on coherent combination can be neglected.