LAser Spectroscopy of sImple MUonic atomS

我们的目标是用相对精度为1ppm的介子氢和介子氦-3离子的基态(1S)超精细分裂(HFS)的第一个激光光谱。这产生了相应的质子和氦-3核的核性质，精度提高了100倍。这项提议涉及激光系统的构建、腔体和数据获取。缪子原子是一种奇特的原子，其中轨道上的电子被一个负的µ子所取代。由于Muon的质量是电子的200倍，Muon的玻尔半径小200倍，Muon和原子核之间的波函数重叠是2003=800万倍。因此，缪子原子对核参数非常敏感，比如它的大小。即使是最简单的原子核，质子，也是一个具有内部结构的扩展物体，由夸克和胶子组成。我们首次通过测量介子氢中的2S Lamb位移确定了质子的电荷半径[Pohl，Antognini，Nez等人，自然，466,213(2010)]。电荷半径量化了质子内部电荷的平均扩展，我们的值比常规氢和弹性电子-质子散射的世界平均测量精度高10倍，但相差超过5个标准差。拟议的HFS测量将使所谓的核双光子交换(TPE)贡献提高100倍，其弹性部分对原子核内部的磁化分布非常敏感。这可以用所谓的(磁)Zemach半径来参数化，我们将把它提高10倍以上。Zemach半径的不确定性将常规氢的HFS中的QED测试限制在6位数，而50年前就已经测量到了12位精度的实验(著名的“21厘米线”)。因此，我们的测量将把氢和氦-3中的QED测试改进一个数量级。Muonic HFS测量将在瑞士保罗-谢勒研究所(PSI)的国际CREMA合作框架内进行。本提议的目标是为CREMA建立中红外激光系统和高速数据采集(DAQ)。新型光学参量振荡器(OPO)将被用来产生中红外的大脉冲能量。在这笔赠款的资助下，F.Nez(LKB)提供精确的激光频率测量和校准，R.Pohl(JGU)为Muonic原子光谱学和DAQ提供多程腔。A.Antognini(PSI)将从他现有的资金中提供一条改进的Muon光束线和高功率脉冲泵浦激光器。基于OPO的光谱激光器将由我们三人通过DFG-ANR赠款进行制造和测试。在这个频率范围内，激光的研究和使用正在增长，在光谱学、激光雷达、玻璃的精密加工、新的生物分子分析技术和新的激光疗法中得到了应用。

We aim at the first laser spectroscopy of the ground state (1S) hyperfine splitting (HFS) of muonic hydrogen and the muonic helium-3 ion with a relative accuracy of 1 ppm. This yields the corresponding nuclear properties of the proton and helium-3 nucleus with 100fold improved precision. This proposal concerns the construction of the laser system, cavities and data acquisition.Muonic atoms are exotic atoms in which the orbiting electrons are replaced by a single negative muon. As the muon is 200 times heavier than an electron, the muon’s Bohr radius is 200 times smaller, and the wave function overlap between muon and nucleus is 2003 = 8 million times larger. Muonic atoms are thus extremely sensitive to nuclear parameters, such as its size.Even the simplest nucleus, the proton, is an extended object with an internal structure, composed of quarks and gluons. We have for the first time determined the proton’s charge radius from the measurement of the 2S Lamb shift in muonic hydrogen [Pohl, Antognini, Nez et al., Nature 466, 213 (2010)]. The charge radius quantifies the average extension of the electric charge inside the proton, and our value is ten times more accurate than the world average from the measurements in regular hydrogen and from elastic electron-proton scattering, but differs by more than 5 standard deviations.The proposed HFS measurement will improve by a factor of 100 the so-called nuclear two-photon exchange (TPE) contribution, the elastic part of which is sensitive to the magnetization distribution inside the nucleus. This can be parametrized in terms of the so-called (magnetic) Zemach radius, which we will improve by more than a factor of 10.The uncertainty in the Zemach radius limits the QED test in the HFS of regular hydrogen to 6 digits, while experiment (the famous „21-cm line“) has been measured with 12 digits accuracy already 50 years ago. Our measurements will thus improve the QED test in hydrogen and helium-3 by an order of magnitude.The muonic HFS measurements will take place at the Swiss Paul-Scherrer-Institute (PSI) in the framework of the international CREMA collaboration. The goal of the present proposal is to build the mid-IR laser systems and high-rate data acquisition (DAQ) for CREMA. Novel optical parametric oscillators (OPOs) will be used to generate the large pulse energies in the mid-IR. Funded by this grant, F. Nez (LKB) provides accurate laser frequency measurement and calibration, R. Pohl (JGU) contributes the multipass-cavity for muonic atom spectroscopy and DAQ. A. Antognini (PSI) will from his existing funding provide an improved muon beam line and high-power pulsed pump laser. The OPO-based spectroscopy laser will be built and tested by all three of us through this DFG-ANR grant. The study and use of lasers in this frequency range is growing, with applications in spectroscopy, LIDAR, precise machining of glass, new bio-molecular analysis techniques and new laser therapies.