Thin-disk laser for muonic atoms spectroscopy

在瑞士的Paul Scherrer研究所，我们最近用激光光谱学的方法测量了介子氢(由负的介子和质子形成的原子)中的2S-2P能量差，使我们能够确定质子的均方根电荷半径。新的质子半径值0.84184(67)fm比以前获得的精度高10倍。然而，它与氢谱提取的值有4个标准差，与电子-质子散射数据也有5个标准差。这些差异的来源尚不清楚。它可能来自类氢原子理论，也可能来自最准确的已知基本常数(里德堡常数)的确定问题，或者来自意想不到的质子形状，或者来自未计算的或新的效应。各种质子半径值的变化在不同的物理领域引起了非常活跃的讨论：粒子和核物理(质子结构，新物理，散射分析)，原子物理(氢能级理论，基本常数)和基础理论(束缚态问题，QED，有效场论)。一些新的实验和提议也在世界范围内被触发。为了揭示这个质子半径难题，我们计划测量Muonic HE3和HE4离子中2S和2P态之间的几个跃迁频率。除了帮助解决质子半径之谜外，这些测量还将导致对阿尔法粒子和氦离子有效电荷半径的最佳确定，相对精度至少为0.03%，对应的绝对精度为0.0005 fM。这些半径代表了有趣和精确的参数来检验少核子从头计算、有效场核理论和势。此外，当与He+的1S-2S跃迁相结合时，这些测量将引起对类氢原子中关键的QED项的最准确的测试。在本申请中描述的这个项目的主要目标是发展一种适合测量Muonic氦中的几个2S-2P跃迁的薄盘激光器。这项工作的挑战是实现一个脉冲能量至少150mJ(脉宽20 ns)的薄盘激光，触发和发射脉冲之间的延迟小于400 ns，随机触发的重复频率高达1kHz。除了对缪子氦的精确光谱是必要的外，这个激光系统还可能在Muon自旋共振领域找到有趣的应用，并为开发新的薄盘激光技术提供潜力。A.Antognini，ETHZ(前Max Planck Institut für Quantenoptik)和IFSW合作开发了一个薄盘激光系统，用于Muonic氢兰姆移动实验。这一进展使得在2009年PSI的束流时间测量质子半径成为可能。与低能量光束线一起，这是测量所需的最具挑战性的开发。通过这个项目，我们希望提高这个薄盘激光系统的脉冲能量、稳定性和可靠性，特别是鉴于Muonic He Lamb Shift实验(该实验已获得PSI国际粒子物理研究委员会的批准)。通过这个项目，我们想要开发一种薄盘激光振荡器，其脉冲能量高达60mJ(约20 ns长)，延迟约250 ns。与目前的设置相比，这是能量增加了6倍。此外，我们将把我们的多程放大器的性能提高到输出150mJ的脉冲能量(增加了3倍)。这些发展可以在高功率(千瓦功率)连续波和飞秒体制中得到应用，并有助于薄盘技术的进步。根据PSI的新建议，这种具有高脉冲能量和短延迟的激光器也适用于未来的Muon自旋共振应用。对于这个项目，在ETHZ和IFSW之间的DACH合作框架内，我们要求2名博士生支持：每个相关研究所一名。这些学生不仅将致力于薄盘激光及其相关技术的发展，还将致力于穆斯介子氦的光谱学。

At the Paul Scherrer Institute, Switzerland, we have recently measured the 2S-2P energy difference in muonic hydrogen (an atom formed by a negative muon and a proton) by means of laser spectroscopy, allowing us to determine the rms charge radius of the proton. The new proton radius value of 0.84184(67) fm is 10 times more precise than previously obtained. However, it disagrees by 4 standard deviations from the value extracted from hydrogen spectroscopy and also by 5 standard deviations from electron-proton scattering data. The origin of the discrepancies is not yet known. It may come either from hydrogen-like atoms theory, or from a problem in the determination of the most accurately know fundamental constant (the Rydberg constant), or from an unexpected proton shape, or it occurs from uncalculated or new effects.The variance of the various proton radius values has led to a very alive discussion in various field of physics: particle and nuclear physics (proton structure, new physics, scattering analysis), in atomic physics (hydrogen energy level theory, fundamental constants) and fundamental theories (bound-state problems, QED, effective field theories). Several new experiments and proposals have also been triggered worldwide.In order to shed some light onto this proton radius conundrum we plan to measure several transition frequencies between the 2S and the 2P states in muonic He3 and He4 ions. Beside helping to solve the proton radius puzzle these measurements will result in the best determination of the alpha-particle and helion rms charge radii to a relative accuracy of at least 0.03% corresponding to an absolute precision of 0.0005 fm. These radii represent interesting and precise parameters to check few-nucleon ab-initio calculations, effective field nuclear theories and potentials.Furthermore when combined with the 1S-2S transition in He+ these measurements will give rise to the most accurate test of the crucial QED terms in hydrogen-like atoms.The main goal of this project described in this application is the development of a thin-disk laser suited for the measurements of several 2S-2P transitions in muonic helium. The challenge for this work is the realization of a thin-disk laser with at least 150 mJ pulse energy (with 20 ns pulse width), a delay between trigger and emission of the pulse smaller than 400 ns, random triggerable to repetition rates up to 1kHz.Beside being necessary for precision spectroscopy of muonic helium this laser system may find an interesting application in the field of muon spin resonance and holds the potential for the development of new thin-disk laser technologies.A thin-disk laser system has been already developed in a collaboration between A. Antognini, ETHZ (former Max Planck Institut für Quantenoptik) and the IFSW for the muonic hydrogen Lamb shift experiment. This development has enabled the measurement in beam time 2009 at PSI of the proton radius. Together with the low-energy beam line it was the most challenging development necessary for this measurement.With this project our collaboration would like to improve the pulse energy, stability and reliability of this thin-disk laser system, particularly in view of the muonic helium Lamb shift experiment (this experiment has been approved by the international research committee for particle physics at the PSI). With this project we would like to develop a thin-disk laser oscillator delivering pulses up to 60 mJ energy (ca 20 ns long) with delays of about 250 ns. This is a factor of 6 increase in energy compared with the present set-up. Moreover we will advance the performance of our multi-pass amplifier to output pulse energies of 150 mJ (a factor of 3 increase). These developments could find application in high power (kW power) cw and fs regimes and contribute to thin-disk technology advances.Such a laser with high pulse energy and short delay is also suited for future muon spin resonance applications in line with new proposals at PSI.For this project, which is in the framework of a DACH collaboration between ETHZ and IFSW, we ask the support for 2 PhD students: one for each involved institute. The students will work not only at the development of the thin-disk laser and related technologies but also at spectroscopy of muonic helium.