PM: Precision Laser Spectroscopy of 2S-nS Two-Photon Transitions in Hydrogen

在这个项目中，激光将被用来探测氢原子的内部量子态。 氢是最简单的原子，只有一个电子和一个质子。由于这种简单性，描述氢的理论发展得非常好，氢的精确测量可以为我们最好的物理理论提供严格的测试，并确定自然界的关键基本常数。 可以通过氢测量确定的一个常数是质子大小，它也可以在高能物理设施中测量，其中电子从质子散射，或者通过测量氢的奇异形式，其中电子被称为μ子的较重基本粒子所取代。 在这些不同的物理系统中对质子大小的测定产生了不一致性，这可能表明我们目前的理论存在问题，或者需要额外的理论。 该项目将通过提供比以前对相同氢状态的测量少一个数量级的不确定性来帮助实现清晰度。计划中的实验将培养学生在原子，分子和光学物理，精密激光科学和精密测量领域。 最终，该项目可以为我们的基本常数提供更可靠的值，建立来自不同物理系统和不同科学学科的物理常数的一致性，或者可能提供新的物理定律的指示。 该项目的目标是对原子氢进行高精度激光光谱分析。要测量的特定跃迁将是氢2S-nS双光子跃迁（n在8和12之间）。 结合成熟的氢理论，这些测量可以用来提取里德伯常数和质子电荷半径。以前在不同的物理系统中对这些常数的测定--如其他氢跃迁、μ子氢的测量和电子散射--产生了不一致性，这可能预示着新的物理学。 光谱将进行低温和速度特征的氢束，光谱激光器将是一个腔增强的连续波钛：蓝宝石激光器参考相干光频率梳。在以前的测量中，AC斯塔克位移加宽和扭曲的光谱共振，引入系统的不确定性。然而，对于这些实验，将使用波长约为650 nm的附加激光器来消除AC斯塔克位移。这种消除将允许恢复窄洛伦兹共振，其宽度接近自然线宽-在50 kHz和144 kHz之间-并且绝对频率测量的相对不确定性小于万亿分之一（12位精度），这代表了一个数量级的不确定性下降比以前的测量这些相同的转变。这一奖项反映了NSF的法定基金会的使命是履行其使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评价，被认为值得支持。

For this project, a laser will be used to probe the internal quantum states of atomic hydrogen. Hydrogen is the simplest atom and is comprised of only one electron and one proton. Due to this simplicity, the theory describing hydrogen is very well-developed and precise measurements in hydrogen can provide a stringent test of our best physical theories and determine key fundamental constants of nature. One constant that can be determined through hydrogen measurements is the proton size, which can also be measured at high-energy physics facilities where electrons are scattered off of protons, or through measurements of an exotic form of hydrogen where the electron is replaced by a heavier fundamental particle called a muon. Determinations of the proton size in these different physical systems have produced inconsistencies, which may be indicating a problem with our current theories, or the need for additional theories. This project will help bring clarity by providing measurements with an order of magnitude less uncertainty over previous measurements of the same hydrogen states. The planned experiments will train students in the fields of atomic, molecular, and optical physics, precision laser science, and precision measurement. Ultimately, this project could provide more reliable values for our fundamental constants, establish consistency in the physical constants derived from different physical systems and within different scientific disciplines, or possibly provide indications of new physical laws. The goal of this project is to perform high-precision laser spectroscopy of atomic hydrogen. The specific transitions to be measured will be the hydrogen 2S-nS two-photon transitions (with n between 8 and 12). In conjunction with well-developed hydrogen theory, these measurements can be used to extract the Rydberg constant and proton charge radius. Previous determinations of these constants in different physical systems – such as other hydrogen transitions, measurements in muonic hydrogen, and electron scattering – have produced inconsistencies which may indicate new physics. The spectroscopy will be performed on a cryogenic and velocity-characterized hydrogen beam, and the spectroscopy laser will be a cavity-enhanced continuous-wave Ti:sapphire laser referenced to a coherent optical frequency comb. In previous measurements, the AC Stark shift broadened and distorted spectroscopic resonances which introduced systematic uncertainty. However, for these experiments, an additional laser with a wavelength of approximately 650 nm will be used to cancel the AC Stark shift. This cancellation will allow for the recovery of narrow Lorentzian resonances with widths approaching the natural linewidths – between 50 kHz and 144 kHz – and absolute frequency measurements with relative uncertainties of less than 1 part in a trillion (twelve digits of accuracy), which represents a one order of magnitude decrease in uncertainty over previous measurements of those same transitions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.