Optical frequency measurement: 40 years of technology revolutions

摘要

The past forty years have witnessed spectacular progress innprecision measurements, beginning with the first coherent opticalnsource, the HeNe CW laser. Almost immediately, the pioneers of thenstable laser epoch introduced optical heterodyne techniques to explorenthe stability of the laser's optical frequency, expecting the fewnmilliHertz linewidth predicted by the Schawlow-Townes formula for phasendiffusion, and instead finding myriad physical processes that broadennand jiggle optical frequencies far beyond that narrow range. After anhuge time and learning effort, most of these technical limitations cannnow be overcome. The paper is intended to offer anbystander/sometimes-participant's view into the advances in laser toolsnand the exciting scientific/technical worlds that were opened by them.nRoughly one "zillion" further clever inventions and techniques havenadded capability to the laser and have enabled many bursts of productivenresearch. Now, after nearly forty years of incremental progress, thenastonishing reality is that within the past one year - absolute opticalnfrequency measurements have suddenly become feasible, simple - evennroutine. This welcome and unexpected progress is based on the merger ofntechniques from the ultrastable lasers and the ultrafast lasers researchncommunities. In a very real sense, these research objectives seem to benthe exact opposites - the most unchanging versus the most quicklynchanging