| Since the 1990s,ultracold atom physics have achieved remarkable accomplishments in field such as accurate measurement,quantum information and quantum simulation,and immensely motivated the theory and experiment study of cold molecule physics.Compared with atoms,the inner structure of molecules are more complex and easier to be controlled by outside field.Therefore,the study of the preparation of ultracold molecules,spectroscopy measurement and outside filed control are very challenging and potential frontier study,and will create more new cross-section studies such as ultracold chemistry,quantum information process and super high resolution molecule spectroscopy.Ultracold molecule is a new kind of molecule produced by synthesize ultracold atoms with laser or magnetic field,it greatly distinct from typical hot molecule:its excited states are mainly high vibrational state molecules,populated in the long range state area of the near disassociation limit,usually called long state molecules or pure long state molecules.Therefore,after obtained the ultracold molecule samples,the primary task is to understand its state structure and to obtain relevant constants and coefficients,and then to build high accurate potential curves,paves the way for the relevant studies based on ultracold molecules.Besides,study the state structure of the long range state helps people understand the physic mechanism of the transfer area between the molecule continua to atom scattering state.The focus of this thesis is based on the problem that for the long range state of ultracold molecules the rotational constants of the high vibrational levels are difficult to measure directly,by developing the double-photoassociation spectroscopy technique and building the accurate frequency inference,we obtained the frequency intervals of the neighboring rotational levels.And then by non-rigid rotor model,we obtained the rotational constants of the high vibrational levels of long range state of ultracold molecules.The main tasks of this thesis include the following content:1.Using the standard magnetical-optical trapping technique,we prepared the ultracold atoms sample with the temperature of 200?K and with the number of 5×10-7 in the cell(10-7Pa).With the use of ultracold atom photoassociation technique,photoassociate colliding ultracold atoms to ultracold cesium molecules;with the use of trap loss technique,detect the photoassociation spectroscopy up to J=0?7 of ultracold molecule long range state high vibrational levels.2.The high vibrational levels of ultracold molecule long range state near disassociation limit range are very intense,the frequency intervals of the neighboring states cannot be obtained by regular method,therefore cannot obtain the rotational constants by fitting.We developed a double-photoassociation method,which is to create an optical frequency reference deliberately.We can obtain the frequency intervals of the neighboring states by the optical frequency reference,prerequisite for the linear scan of the photoassociation laser.In the experiment,the signal-noise ratio of the double-photoassociation spectroscopy we obtained is up to 20.By this technique,we measured the laser induces frequency shift of the ultracold cesium molecules and proved the possibility in minor frequency interval measurement.3.With the double-photoassociation spectroscopy,we obtained the frequency intervals of 0u+ state,v= 187.Then we fitted the experiment data using the non-rigid rotor model considered the weak bound in the long range molecules,obtained the rotational constants and centrifugation distorted constants.Besides,we studied the dependence of the rotational constants in the vibrational quantum number,and its linear relation is found.By the study of this thesis,we developed double-photoassociation technique,obtained the rotational constants of the high level states.The technique can also be expanded to use in the study of line width and the accurate measurement of laser induced frequency shift. |
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