Femtosecond mode-locked lasers producing visible/infrared frequency combs have steadily advanced our understanding of fundamental processes in nature. For example, optical clocks employ frequency-comb techniques for the most precise measurements of time, permitting the search for minuscule drifts of natural constants. Furthermore, the generation of extreme-ultraviolet attosecond bursts synchronized to the electric field of visible/infrared femtosecond pulses affords real-time measurements of electron dynamics in matter. Cavity-enhanced high-order harmonic generation sources uniquely combine broadband vacuum- and extreme-ultraviolet spectral coverage with multimegahertz pulse repetition rates and coherence properties akin to those of frequency combs. Here we review the coming of age of this technology and its recent applications and prospects, including precision frequency-comb spectroscopy of electronic and potentially nuclear transitions, and low-space-charge attosecond-temporal-resolution photoelectron spectroscopy with nearly 100% temporal detection duty cycle.

飞秒锁模激光器产生可见/红外频率梳，稳步推进了我们对自然界基本过程的理解。例如，光学时钟采用频率梳技术来进行最精确的时间测量，从而允许搜索自然常数的微小漂移。此外，与可见/红外飞秒脉冲的电场同步的极紫外阿秒脉冲的产生提供了物质中电子动力学的实时测量。腔增强的高次谐波生成源将宽带真空和极紫外频谱覆盖与兆赫兹脉冲重复频率和相干特性（类似于频率梳）的独特结合在一起。在这里，我们回顾了这项技术的时代来临，以及它的最新应用和前景，