Since the beginning of this millennium, frequency comb generators have reshaped frequency metrology and related areas. After more than two decades since their first realization, several other ways to generate frequency combs, in any spectral region, have been demonstrated, each way with its peculiar features. This trend has triggered the need to quantitatively assess how close the new comb realizations are to an ideal comb, a feature that will be called combness throughout this paper. We will briefly review the very dynamic area of novel frequency comb sources and we will describe the techniques that have been recently developed to quantitatively assess the key parameters of old and new frequency combs, in view of the specific applications. Finally, we will try to sketch future steps in this recently born research area.

中文翻译：

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频率梳源的计量：评估从多模到锁模操作的相干性

自本世纪初以来，频率梳发生器重塑了频率计量及相关领域。自首次实现以来二十多年后，在任何光谱区域生成频率梳的几种其他方法已经被证明，每种方法都有其独特的特征。这种趋势引发了定量评估新的梳子实现与理想梳子的接近程度的需要，这一特征在本文中被称为梳子性。我们将简要回顾新型频率梳源的动态领域，并根据具体应用描述最近开发的用于定量评估新旧频率梳关键参数的技术。最后，我们将尝试勾勒出这个最近诞生的研究领域的未来步骤。