Study Of Impacts Of The Neutral Collision Between Helium And Rubidium On Its Fine Spectra

The neutral nonresonant collision between alkali metal atom and noble gas atom results in the formation of temporally Van der Waals molecule,which in turn changes the energy levels of the alkali atom.Such mechanism can be used to explain the variation of the spectral profile of the alkali atom within different buffer gases,and thus has many important uses in many areas involving the optical pumping of the alkali atoms,such as astrophysics,alkali lasers and hyperpolarized gases.The study of pressure broadening and shift of atomic resonance lines by collisions with neutral atoms have been the subject of considerable interest both theoretically and experimentally.However,the theoretical description for the spectral change of alkali metal in the environment of rare gases is still not perfect,which is manifested in the facts that the full quantum theory cannot correctly describe the dependence of pressure broadening and shift on the ambient gas temperature,while the semi-classical predictions agree well with experimental observations but is still incomplete.Although there are many observations of alkali metals and rare gas combinations in various temperature and pressure ranges,but due to the difference of data analysis methods and the lack of spectral observations in the high and low temperature limit regions,there are significant differences among experimental results.In this work,by using a narrow linewidth continuous laser and lock-in amplification system,the high precision absorption spectroscopy of the rubidium atom D1 and D2 lines are measured in low temperature region.The experimental datas are extensively analyzed to obtain the pressure broadening and shift coefficients,the hyperfine structure of different isotopes and the hyperfine transition strengths were taken into consideration in the analysis.A new calculation method based on Baranger model is used to predict the pressure broadening and shift coefficiets.By using the variable phase method,the scatteing phase shift difference is obtained for every angular momentum,and the pressure broadening and shift coefficients are calculated for tempreatures rangeing from 100 to 800 K,predictions from other calculation models are also compared.The comparisons show the accurancy and advantage of the new method.Compared with the original method,the dependence of the organial quantum method on the thermal velocity distribution is eliminated,the new calculation method is more efficient and time-saving.In addition,the new method is consistent with the experimental observations and semi-classical theoretical predictions in most of the temperature range,which proves the credibility of the calculation results,while the significantly difference in the low temperature might suggest that in low velocity region there is a sizable quantum effect which cannot be experimentally observed so far.A Fabry-Perot etalon is established to improve the precision of the experimental observation.The doppler effect is eliminated by saturation absorption spectroscopy,and the hyperfine splitting of isotopes ⁸⁵Rb and ⁸⁷Rb is experimentally measured,the hyperfine interaction constants are calculated accordingly.