Experimental Study Of Natural Radiation Lifetimes And Landé Factors For High-excited 5p7p Levels In Sn I

Neutral tin(Sn I)is medium weight atom of carbon group element and the nuclear charge number is 50.The ground state electronic configuration of Sn I is 5s²5p² and belongs to even-parity.So far the data about energy level character of Sn I is mainly energy level values while other characteristic parameters do not have perfect research results,such as the natural radiation lifetime,Lande gj factor,hyperfine structure,transition probability and oscillator strength,due to several important reasons.Firstly,the atomic beam of Sn I used in spectral measurement are difficultly produced;Secondly,low-excited levels of Sn I are quite sparse and most of the high-excited levels locate in the ultraviolet band, which brings tremendous difficulties on spectrum measurements.Since the typical excited state of Sn I is consist of an ionic core with p electron going with an excited electron outside,they possess different characteristics compared with ionic core with s electron,which is an interesting point in the theory of atomic structure.Based on the research background mentioned,in this paper,we combined the laser-atomic beam technology with the time-resolved laser-induced fluorescence spectroscopy technology,and used the two-photon two-step excitation methods to measure the natural radiation lifetime and Lande factor of even-parity high-excited 5p7p states of Sn I.The laser system used in the experiment was consisted of two dye lasers pumped by two Nd:YAG lasers,respectively.The beam of neutral atoms was produced in a home-made atomic beam device.The two laser beams interacted with the atomic beam and excited the atom from the low-level to the high-levels to be studied.Then we use a grating monochromator and photomultiplier tube to detect radiation fluorescence signal,and finally we recorded the temporal electric signal by oscilloscope,stored it in a personal computer.The experimental system was necessarily calibrated and checked. Wavelength of laser system was calibrated by measuring natural radiative lifetime of odd-parity levels 6s6p ³P₁ of Yb I.By measureing the quantum beam of the same level and contrasting with the known Lande gj factor we obtained the Current-Magnetic field curve.In order to check the reliability of the vacuum atomic beam system,we measured the lifetime of the 5p6s ³P₁ level using single-photon excitation mode,and the result coincided well with the data that has been published.So that we are sure that the vacuum atomic beam system can produce neutral atomic beam that can be used in the atomic spectrum study.Two-step excitation process was used in experimental study of natural lifetime and Lande factor for high-excited 5p7p levels in Sn I.When the pressure of vacuum chamber was 3.0×10^-3Pa and the temperature of oven was up to 1700K,the atomic beam of Sn populated in the ground state was produced, and then the first laser beam(pump laser)was used to excite the tin atoms to the odd-parity level 5p6s.The second laser beam(probe laser),which was overlapped with the pump beam,was used to achieve particles distribution in even-parity level of Sn I excited states.In the direction of perpendicular to two laser beams,the radiation fluorescence signal was collected by a lens and sent into a monochromator,by which we should choose a suitable observation wavelength.The light signal was converted to electric signal and was amplifed by photomultiplier tube.Finally,the signal was recorded by a oscilloscope and was stored in a personal computer.The current was recorded in time by a multi-meter in experiment and we calculated the magnetic field strength B based on Current-magnetic curve.The natural radiation lifetime values of 5p7p levels Sn I were obtained by fitting an exponential function to the recorded fluorescence curves.The frequency of the quantum beats was obtained by Fourier transforming and contrasting with formulaω₂₁=ΔE/h andΔE=Mg_Jμ_B B,and then we could obtain the Lande factors of 5p7p levels.The natural radiation lifetimes of 9 levels and 8 Lande g_J factors had been measured in experiments.The accuracy of lifetime measurements is effected by blackbody radiation, flight-out-of-view effect,radiative trapping,quantum beats effects and so on, which were briefly described in thesis.Especially for quantum beats effects we had done the relevant experimental studies,and the lifetime values of the levels of the high excited 5p7p state were measured with and without the strong magnetic field added,respectively.The results of experiments showed that without magnetic field,the low frequency quantum beats of fluorescence induced by the geomagnetic field would destroy the pure exponential decay.On the other hand,when the frequency of quantum beats induced by strong magnetic field were so sufficiently high that they exceeded the time resolution of apparatus,the fluorescence decay remained the exponential laws.We calculated Lande factors under LS coupling representation.Comparing with Lande factors measured in our experiments,we analyzed the situation of the coupling of energy levels.The results of this study will help people further understand the energy level structures of Sn I,and provide important atomic data for theoretical modeling on atomic physics,analytical chemistry,and other research areas.