Precision measurements represent a cornerstone in fundamental science. The capability of observing and quantifying subtle phenomena and events allows new discoveries and it confirms or confutes the theories describing our understanding of nature. The optical frequency comb, providing hundreds of thousands of phase-locked and evenly spaced laser lines, is one of the most fascinating enabling optical technologies and it is the result of a continuous pursuit for precision. Within the two decades from its inception, it has become a key instrument in many laboratories and has revolutionized numerous fields, spanning from time, frequency and length metrology to attosecond physics, gas-sensing and molecular fingerprinting. In this letter we summarize some steps of an exciting journey started 20 years ago, with a certain focus on the authors’ contribution, finally leading to the demonstration of frequency measurements at the 20th decimal digit, and we show some prospective developments.

中文翻译：

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20 年和 20 位小数：光频梳之旅

精密测量是基础科学的基石。观察和量化微妙现象和事件的能力允许新的发现，它证实或驳斥了描述我们对自然理解的理论。光频梳可提供数十万条锁相且间隔均匀的激光线，是最令人着迷的光学技术之一，它是对精度不断追求的结果。自问世以来的 20 年里，它已成为许多实验室的关键仪器，并彻底改变了许多领域，从时间、频率和长度计量到阿秒物理学、气体传感和分子指纹识别。在这封信中，我们总结了 20 年前开始的激动人心的旅程的一些步骤，并重点关注作者的贡献，