Experiment Research On Isotope-selective Photon Ionization Of Mercury Atoms

The optical frequency standard is regarded as the next generation of the time-frequency standard.The accuracy of optical frequency standard is 3-5 orders higher than that of microwave frequency standard,which means optical frequency standard has a higher time-frequency stability.Mercury ion optical frequency standard is one of the earliest ion optical frequency standard in the world,which is also the representative of the definition of the future seconds.In the current mercury ion optical frequency standard system,the common method to obtain the Hg+ion is ionizing the mercury atom with electron bombardment.Mercury atom vapor was produced by thermal decomposition of mercury oxide powder before.This method has several disadvantages,such as low ionizing efficiency,coming into stray electric field,and contamination of the ion trap system.To deal with those problems,in our experiment we acquire the mercury ions using isotope-selective photo ionization,further realizing stable ion frequency standard.In this paper,a laser system for photoionization is designed and fabricated,and the selective photoionization of mercury isotopes is studied experimentally.Firstly,the mercury atoms are pumped to the excited 6s6p state from the ground state using homemade 253.7nm laser and different mercury isotopes can be excited by adjusting the wavelength.Then 194nm laser ionize the selected excited state mercury atoms.On the other hand,the 194nm laser is used for ion cooling in the experiment of mercury ion trapping.Finally,we have observed the fluorescence signal of the excited state mercury atom and successfully trapped mercury ion crystals in a linear ion trap at room temperature.The spectrum of the 6s~2-6s6p transition of the mercury atom are given.In addition to the above work,some theoretical calculations have also been carried out for a prospective highly charged ion(HCI)clock with higher accuracy in this paper.We propose that HCI with three p-valence shell electrons(nitrogen-like sequence)can be the candidate by investigating the M1 and E2 forbidden transition properties of the fine-structure with GRASP 2K.A promising candidate for highly charged ion clock with a quality factor(Q)of transition is given.