The basic properties of atomic nuclei including spins,magnetic moments,electric quadrupole moments and charge radii,are sensitive probes to different aspects of exotic nuclear structure,and are also important to investigate the unrevealed nature of interaction between nucleons.Based on multidiscipline,laser spectroscopy is a unique tool to precisely measure the basic nuclear properties mentioned above in a nuclear-model independent way by measuring the hyperfine structure of atoms,ions,or molecules,which has played an important role in the study of exotic nuclear structures across the different regions of the nuclear chart.Basic principles of laser spectroscopy and various types of experimental devices are expounded after the brief history of the hyperfine structure.Furthermore,advantages of utilizing laser spectroscopy in the study of nuclear struc-ture are briefly introduced by taking the radioactive neutron-deficient Pb region as an illustration.In addition,current condi-tion of collinear laser spectroscopy setup has been systematically reviewed,together with the latest progress on collinear res-onance ionization spectroscopy offline devices at Peking University.Finally,the developing status and ongoing plan of laser spectroscopy devices for current and future radioactive ion beam facilities in China have been put forward,and the broad pro-spects of laser spectroscopy in unstable nuclear properties and the fundamental symmetries based on molecular spectroscopy are interpreted.

The basic properties of unstable nuclei are very sensitive probes for the study of exotic nuclear structures, which is of importance for an in-depth understanding of the unexpected structure phenomena in atomic nuclei with large proton-toneutron ratios. Collinear laser spectroscopy (CLS) techniques have been proven to be a powerful tool to determine simultaneously multiple fundamental properties of ground and long-lived isomeric states of exotic nuclei, such as nuclear spins, electromagnetic moments and charge radii, by measuring the subtle hyperfine structure and isotope shifts in a nuclear model-independent manner. The studies of nuclear properties and structures of unstable nuclei using laser spectroscopy have been broadly carried out at ISOL (Isotope Separator On-Line)-type radioactive ion beam (RIB) facilitates, such as ISOLDE at CERN, IGISOL at JYFL and ISAC at TRIUMF, where the low energy RI beam is directly offered with highquality. With the goal to explore more exotic nuclei, laser spectroscopy techniques, with their continuous technological development towards higher resolution and higher sensitivity, have been broadly established and planned at current- and next-generation RIB facilities worldwide. This CLS technique, however, has not yet been implemented at current operational domestic RIB facilities, the PF (Projectile Fragmentation)-type HIRFL at IMP and the BRIF (ISOL-type) at CIAE, for the studies of nuclear properties of unstable nuclei. Thus, we have recently developed a fluorescence-detection-based CLS system, which has been commissioned with stable ion beam produced from an offline laser ablation ion source and radioactive ion beam from BRIF RIB facility. In this paper, we briefly introduce the recent progress on the development of laser spectroscopy techniques at RIB facilities worldwide, as well as the experimental methods to measure the hyperfine structure spectra. Subsequently, the details of the CLS system recently developed, are presented together with recent upgrades and offline test. The optimization and upgrade of this system, include the lens rotator system for laser spot control, ion beam imaging using a phosphor screen, and calibration of the neutralization efficiency of the change exchange process. Based on these upgrades, we performed the offline test experiment using stable Ca and Ti beams. The optical spectra for the 4s S-2(1/2) -> 4p (2) P-3/2 ionic transition of Ca-40(+) and for the 3d(2)4s(23)F(2) -> 3d(3) 4p (3) D-1 atomic transition of Ti-48 were obtained, giving a spectral linewidth of approximately 55 MHz for Ca and 65 MHz for Ti. The total detection sensitivity estimated in the case of Ca-40(+) is comparable to that of the well-established CLS setups worldwide. Finally, a summary and outlook on the further development of the collinear resonance ionization spectroscopy towards higher sensitivity are given, which will be used at the current and future RIB facilities in China for the study of unstable nuclei with shorter half-lives and lower production yield. Further implementation of the UCx target into the BRIF facility is currently on-going, which will potentially produce more exotic isotopes at different mass regions. Development and installation of a radiofrequency quadrupole cooler and buncher are also on-going, which could provide bunched ion beams with low energy spread of few electron volts, being essential for the high resolution and high sensitivity measurement of unstable nuclei using CLS.

A control and data acquisition system was implemented for the recently developed collinear laser spectroscopy setup. This system is dedicated to data recording, storage, processing, monitoring of the beam intensity and energy, and visualization of various spectra. In comparison to the conventional resonance nuclear reaction system, the key technique is the precise synchronization of the detected counts with the actual scanning voltage (or probing laser frequency). The functions of the system were tested by measuring the hyperfine structure spectra of stable calcium (e.g.,40Ca+) and radioactive potassium (e.g., 38K) in the bunched and continuous modes, respectively. This system will be routinely applied and further improved in subsequent laser spectroscopy experiments on unstable isotopes at the Beijing Radioactive Ion-beam Facility (BRIF).

不稳定原子核的基本性质反映了核的内在结构和有效相互作用,可用于研究不稳定核的奇特结构.激光核谱技术通过测量核外电子光谱的超精细结构和同位素移位,可以核模型无关地提取原子核的多个基本性质,是研究不稳定核性质和结构的有力工具之一.多步激光共振电离方法是测量原子或离子超精细结构和同位素移位的方法之一.基于此,国际上发展了多种共振电离谱实验技术,用于放射性核束装置上开展不稳定核基本性质和结构研究.本文首先介绍了激光共振电离方法,以及由此发展的各种共振电离激光谱实验技术.随后详细讨论了近十年来刚发展起来的共线共振电离谱技术.此技术可同时实现超精细结构谱的高分辨和高灵敏度测量,正在核素版图大质量范围内的不稳定核性质和结构研究中发挥重要作用.最后分析了用于国内放射性核束装置的共振电离激光谱技术的发展现状及应用前景.

Collinear laser spectroscopy is a powerful tool for studying the nuclear spins, electromagnetic moments, and charge radii of exotic nuclei. To study the nuclear properties of unstable nuclei at the Beijing Radioactive Ion-beam Facility (BRIF) and the future High Intensity Heavy-ion Accelerator Facility (HIAF), we developed a collinear laser spectroscopy apparatus integrated with an offline laser ablation ion source and a laser system. The overall performance of this state-of-the-art technique was evaluated, and the system was commissioned using a bunched stable ion beam. The high-resolution optical spectra for the 4 s ^2S_1/2 → 4 p ^2P_3/2 (D2) ionic transition of ^40,42,44,48 Ca isotopes were successfully measured. The extracted isotope shifts relative to ^40 Ca showed excellent agreement with the literature values. This system is now ready for use at radioactive ion beam facilities such as the BRIF and paves the way for the further development of higher-sensitivity collinear resonance ionization spectroscopy techniques.