Lifetime Measurements Of Odd-parity High-excited Levels Of Sm Ⅱ By Time-resolved Laser Spectroscopy

Abundance of the elements refers to the relative content of chemical elements and isotopes in all kinds of objects. It is the basis to explain evolution process of celestial objects. In recent years, more and more nova and new astronomical phenomenon was found by advanced astronomical observation technology, and the analysis of their chemical components has become a problem that need people urgently to solve. Astrospectroscopy is the subject which could solve the problem. First, we change the light wave which was radiated or reflected from celestial objects into the optical spectrum by physical method (especially optical method), then according to the spectral analysis theory and the theory of modern physics (especially theoretical physics and atomic spectroscopy), we can analyze the chemical structure of celestial objects. But we need abundant spectra data as the basic to get the exact analysis results, so perfecting the spectral data of important elements as early as possible become an important problem to analysis the development and constitute of celestial objects. With the advent of laser, laser spectroscopy has become an important subject and it can provide reliable technical support for us to measure the exact spectra data. So it is the highly opportune moment for us to carry out the relevant research.In astrophysics, people put more attention in abundance of heavy elements. For many stars, nuclei synthesis theory model of heavy elements (especially the sixth cycle elements) need exact data of emission transition to test and verify. Therefore, it is important for these data to ascertain the exact abundance of elements by intensity of spectral line of celestial objects. Samarium is one of the lanthanide series elements which belong to the sixth cycle elements and its atomic number is 62. From the early 1970s, people gradually verified the spectral lines of Smâ… , Smâ…¡and Smâ…¢in some celestial objects, and the spectral lines of Smâ…¡take a high content. So the exact lifetime measurements of high-excitation levels of Smâ…¡will help people to further recognize celestial objects. Till now, the lifetime of some levels of Smâ…¡has been measured, but due to the complexity of level structure of Smâ…¡, some high-excitation levels radiation (especially ultraviolet radiation) lifetime haven't been researched sufficiently. While the ultraviolet radiation may take important position in astronomical spectra, so we choose Smâ…¡as our research object.Time-resolved laser-induced fluorescence spectra technology is one of the spectral skills that could resolve the physical change within short time. Its most typical application is to measure the lifetime of radio fluorescence. Due to the high strength of laser, time-resolved laser-induced fluorescence spectra technology can excite the high-excitation levels and the levels which have small transition probability. So we take the measurement of the lifetime by this technology.Smâ…¡has different transition probability from the excitation levels to low levels and is limited by selection rule, so we could not excite all the Smâ…¡from ground level, but choose some metastable levels and low excitation levels as initial levels to measure more radiation lifetime of excitation levels. As we know, the plasma produced by laser-induced could make the metastable levels and low excitation levels have enough population. So we take the laser produced plasma technology to get the ion source. But because the ion source contains Sm atoms and other Sm ions, the spectral line of ions become very complicated. Therefore, we needed to collect the levels of Sm atoms and ions as possible as we can. Through this, we could choose appropriate excited channel.When we was measuring the lifetime, we applied an appropriate intense magnetic field around the plasma to avoid the error of lifetime produced by instability of ions source, and it could remove the influence of quantum beat effect at the same time. Then, we increased the delay time on a large scale between excitation pulse and etching pulse to reduce the influence of other effects. In addition, we also needed to choose an appropriate width of monochrometer's slit. At last, we tried our best to choose the observe channel which has much more strong fluorescence intensity and each collected signal was obtained by 2000 times average of excitation fluorescence curves. For long lifetime levels, we got the value of lifetime by e-exponential curve fitting. While for short lifetime levels, in order to eliminate the influence of pulse width of exciting light and response function of detection system, we used e-exponential curve with varying parameter and light exciting pulse curve recorded by the same detection system to do convolution, then we got the value of lifetime by fitting fluorescence attenuation curve with the convolution.We took the measure about the lifetime of odd-parity high-excitation levels of Smâ…¡by laser produced plasma technology and time-resolved laser-induced fluorescence spectra technology, then we fitted the collected fluorescence attenuation curve by e-exponential and analyzed the error of lifetime by error theory. As a result, natural radiative lifetimes of 53 odd-parity highly excited levels of singly ionized samarium in the energy range from 26599.08 to 36107.66 cm-1 have been measured, and there were 7 high excitation levels above 35000 cm-1. The lifetime values obtained in this paper are in the range from 10.5 to 271.4 ns. When a comparison between the present results and a large number of previously published values was accomplished, a good agreement was achieved. The measured lifetimes of this paper provided data for astronomical spectral analysis and it will be useful for investigating the composition of chemically peculiar stars.