Strong correlations between the signal and idler beams imprinted during their generation dominantly determine the properties of twin beams. They are also responsible for the waves in intensity coherence observed in the wave-vector space of a twin beam propagating in a nonlinear crystal in the regime with pump depletion. These waves start to develop at certain twin-beam intensities and move from the signal- and idler-beam centers towards their tails. They manifest themselves via the change of coherence volume monitored in the far field by the measurement of local modified ${\overline{g}}^{\left(2\right)}$ function, which acts as a sensitive and stable tool for investigating field intensity coherence.

中文翻译：

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演化的强双束光的强度相干波

信号和闲置光束在其生成过程中所产生的强相关性决定了双光束的特性。它们还负责在泵浦耗尽状态下在非线性晶体中传播的双光束在波矢量空间中观察到的强度相干波。这些波以一定的双光束强度开始发展，并从信号束和惰束中心向尾部移动。它们通过在远场中通过测量局部修正来监测相干体积的变化来体现自己${\overline{G}}^{（2）}$ 功能，它是研究场强相干性的敏感而稳定的工具。