Precision Spectroscopy Of The 2~3S-2~3P Transitions In Atomic Helium

Precision measurement in few-electron atomic systems played an important role in testing fundamental physics and the determination of fundamental physical constants throughout the past few decades.Atomic helium,as the simplest multi-electron system,its energy levels can be calculated with a very high precision by means of Ab-initio calculations,and can be accurately determined using precision spectroscopy.Test of quantum theories can be achieved by comparing theoretical predictions and experimen-tal results.In case of any disagreement,it might imply that there are some undiscov-ered systematic effects,or might signal physics beyond the Standard Model.Particu-larly,the 23Pj energy level in atomic helium,taking advantages of its longer lifetime(≈98 ns)and larger interval(≈ 32 GHz)than the 2P level in atomic hydrogen,is considered as one of the best atomic system for determining the fine-structure constantα.To date,QED calculations of the 23Pj fine-structure splitting have been extended to the α7m corrections with an accuracy of 1.7 kHz,while the experimental result for the 23P0—23P2 splitting is determined by our group with an uncertainty of 130 Hz(4 ppb),which agrees well with the latest theoretical predictions and confirms QED calculations up to the a7m terms.High precision helium spectroscopy can also be used for setting constraints on exotic spin-dependent interactions,and may provide an accurate deter-mination of the helium nuclear charge radius,which could be more precise than that from electron scattering.Moreover,comparisons of results from electronic and muonic helium may provide a sensitive test of universality in electromagnetic interactions of leptons,and may help solve the so-called "proton size puzzle".This thesis is based on precision spectroscopy of helium using a transversely-cooled metastable atomic beamline established in our group.The contents include mea-surements of the fine-structure splitting of 23PJ levels,metrology of the 23 S-23P transition,and studies of the light force shift induced by standing-wave.Chapter 1 includes a brief introduction of the history and developments of precision spectroscopy in few-electron systems.Chapter 2 decribes our experimental schemes and experimental principles.Chapter 3 provides the determination of the 23PJ fine-structure splitting and analysis of systematic effects including the quantum interference effect.Chapter 4 presents measurements of the 23S—23P transition centroid frequency and the determination of helium nuclear charge radius.Chapter 5 discusses studies of the light force shift induced by standing-wave,which contains imaging of atomic profiles and Monte-Carlo wave-function approach for simulating the atomic trajectories.Chapter 6 presents our preparation for3 He,including calculations of Zeeman effect and laser cooling transition frequencies.Chapter 7 summarizes my contributions during Ph.D.and presents brief prospects of our projects.