Creation Of Ultracold NaCs Polar Molecules By Photoassociation And Spectral Measurement Of A~1?~+ State

In the past twenty years,the research on ultra-cold molecules has attracted great interest,especially the polar molecules of ultracold heteronuclear.The unique advantages of ultracold heteronuclear polar molecules are the key to their superiority over neutral ultracold atoms and ultracold homonuclear molecules,which makes the study of ultracold heteronuclear polar molecules gradually applied to the research on precision measurement,ultracold chemistry,simulation of multi-body quantum system,and quantum information processing.Currently,the common used method for the preparation of ultracold molecules is the ultracold atoms' photoassociation.Phototassociation is not only a simple and effective way to complete the preparation of molecules,but also can measure the hyperfine structure spectra of corresponding molecular states with high resolution by combining with the trap-loss spectroscopy technology of modulationdemodulation and noise reduction.The high-resolution spectra of ultracold molecules carry relevant data of molecular states.Through detailed analysis of spectra,the data obtained through analysis and the fitting of the model can be used to fit and calculate the long-range molecular coefficient of corresponding electronic states,which is used to complete the construction of molecular electronic state energy curve model.The molecular potential energy curve is an important reference to understand the molecular internal structure and molecular dynamics,and also provides an advance guidance for the preparation of absolute ground state molecules.In this article,we introduced the photoassociational preparation of ultracold Na Cs polar molecules and high resolution ro-vibrational spectra detection,then the spectral data were analyzed in detail,through specific algorithm for fitting the spectral data to theory model,we got the long-range state molecular coefficients,using diatomic molecular potential energy curveIII model,we got the molecular long-range state experiential potential energy curve.The main work mentioned in this paper can be summarized into three aspects:1.Taking the cooling and trapping of sodium and cesium atoms as the starting point,a complete photoassociation system,a highly sensitive detection system,the vacuum system and the experimental optical path system were established.The atomic initial temperature and atoms number(density)in the dual species dark magneto-optical trap are guaranteed.2.Realized the photoassociation of ultracold sodium atoms and ultracold caesium atoms,using the trap-loss spectra detection technology,combined with the modulation and demodulation of the noise reduction technology,we obtained 10 high resolution spectrum at different vibration level of ultracold Na Cs polar molecular A~1?~ + long-range state3.Through the analysis to the spectra,the binding energy data of the long range state was obtained.Levenberg-marquardt algorithm of fitting curve was used in Mathematica,and the improved Le Roy-Bernstein model was used to fit the obtained binding energy data.Therefore,the molecular coefficient of the sodium-cesium molecule in this long range state was calculated.The potential energy curve of the long-range molecular state is constructed by using the relation between the diatomic molecular coefficient and the potential energy curve.At the same time,we also compared the results of this work with other theoretical values and experimental results,and the results showed that the experimental results were in good agreement with the theoretical values.We also described the applicability of the improved Le Roy-Bernstein model,especially for the application of ultracold sodium-caesium heteronuclear polar molecules.