Gründeman Elmer L, Barbé Vincent, Martínez de Velasco Andrés, Roth Charlaine, Collombon Mathieu, Krauth Julian J, Dreissen Laura S, Taïeb Richard, Eikema Kjeld S E
LaserLaB, Department of Physics and Astronomy, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, the Netherlands.
Sorbonne Université, CNRS, Laboratoire de Chimie Physique-Matière et Rayonnement, LCPMR, F-75005 Paris Cedex 05, France.
Commun Phys. 2024;7(1):414. doi: 10.1038/s42005-024-01891-4. Epub 2024 Dec 19.
Laser spectroscopy of atomic hydrogen and hydrogen-like atoms is a powerful tool for tests of fundamental physics. The 1-2 transition of hydrogen in particular is a cornerstone for stringent Quantum Electrodynamics (QED) tests and for an accurate determination of the Rydberg constant. We report laser excitation of the 1-2 transition in singly-ionized helium (He), a hydrogen-like ion with much higher sensitivity to QED than hydrogen itself. The transition requires two-photon excitation in the challenging extreme ultraviolet wavelength range, which we achieve with a tabletop coherent laser system suitable for precision spectroscopy. The transition is excited by combining an ultrafast amplified pulse at 790 nm (derived from a frequency comb laser) with its 25th harmonic at 32 nm (produced by high-harmonic generation). The results are well described by our simulations and we achieve a sizable 2S excitation fraction of 10 per pulse, paving the way for future precision studies.
原子氢和类氢原子的激光光谱学是基础物理学测试的有力工具。特别是氢的1-2跃迁，是严格的量子电动力学（QED）测试以及精确测定里德伯常数的基石。我们报告了对单离子化氦（He）中1-2跃迁的激光激发，He是一种类氢离子，对QED的敏感度比氢本身高得多。该跃迁需要在具有挑战性的极紫外波长范围内进行双光子激发，我们通过适用于精密光谱学的桌面型相干激光系统实现了这一点。通过将790nm处的超快放大脉冲（源自频率梳激光器）与其32nm处的第25次谐波（通过高次谐波产生）相结合来激发该跃迁。我们的模拟很好地描述了结果，并且每个脉冲实现了可观的10%的2S激发分数，为未来的精密研究铺平了道路。
