Theoretical Studies On Novel Schemes Of Optical Stark Deceleration And Trapping For Molecules

The cooling of atomic species has played a pivotal role in the fields of atom optics, ultracold physics and Bose-Einstein condensation, because it provides a unique and favorable a research platform for condensed matter and quantum information physics. Recently, considerable attention has turned to the creation of cold or ultra-cold molecules because they provide many new interactions, which are not available in cold atomic species. Cold stationary molecules offer an ideal testing ground for ultrahigh resolution molecular-beam spectroscopy, ultracold chemistry and collisions as well as the possibility of a molecular Bose-Einstein condensation. This thesis will focus our attentions on the theoretically study and analysis of the preparation and trap of cold or ultracold molecules by proposing a series of new optical Stark decelerator and storage ring schemes.Firstly, we propose a robust and desirable scheme to realize the deceleration of a pulsed subsonic molecular beam by using a multistage optical Stark decelerator (i.e., a1D quasi-cw, cavity-enhanced optical lattice), which is composed of two nearly counter-propagating, time-varying, red-detuned, light fields with a intensity of～108Wcm-2in a folded ring resonator. The dependences of the molecular slowing effects on the synchronous phase angle, the deceleration stage number and cavity enhancement factor are investigated by3D Monte-Carlo method. Our study shows that the proposed decelerator cannot only be used to slow a pulsed subsonic beam from240m/s to standstill, but also to obtain a cold molecular packet with a temperature of a few μK due to the bunching effect of our multistage optical Stark decelerator, and the corresponding fraction of cold molecules is10-4-10-6, which strongly depends on the synchronous phase angle.Secondly, we propose two promising schemes to realize the deceleration of a pulsed subsonic molecular beam by using a multistage optical Stark decelerator, which is composed of two nearly counter-propagating, time-varying, red-detuned light fields with an intensity of～107Wcm-2and a fixed or a linearly-reduced frequency difference between them. We investigate their operating characteristics and slow effects for molecules by using3D Monte-Carlo simulations respectively. Our study show that both of these proposed decelerators can not only be used to slow a pulsed subsonic beam from240m/s to standstill, but also to obtain a cold molecular packet with a temperature of a few μK, and the corresponding fraction of cold molecules is10-6-10-7and10-5-10-7respectively.Afterwards, in order to form a multistage optical Stark decelerator by using a semi-Gaussian beam, we propose an all-optical storage ring (OSR) scheme composed of a focused, cavity-enhanced, red-detuned hollow beam, which will be formed by using an annular confocal cavity to focus a collimated red-detuned incident hollow beam. By using the numerical calculations of self-reproduction mode in an open cavity, we obtain the stable intensity distribution of the OSR and its optical potential for I2molecules. In order to demonstrate the feasibility of our OSR, we study the loading and guiding dynamics of cold12molecules in the OSR by using Monte-Carlo method, and obtain some important results.In final, we propose a novel multistage optical Stark decelerator by using the above OSR and a pseudo-thermal, semi-Gaussian light (SGB) field, and study its slowing effects for pulsed I2molecular beam by Monte-Carlo simulations. Also, we investigate the dependences of the tangential velocity of molecules, the opened time ton and closed time toff of SGB in each stage on the deceleration-stage number m, and the influence of power Po of SGB on the final tangential velocity of molecules. The results show that (1) the lower the initial molecular velocity vo is, the smaller the stage number m needed for molecules to be slowed to～1m/s will be;(2) with the rise of m, ton and toff will also be lengthened;(3) with the increase of Po from100W to1000W, the final tangential velocity of molecules will be lowered from18.98m/s to1.59m/s when v0=20m/s and m=260. Obviously, this novel multistage optical Stark decelerator can be used to realize the effective slowing of both pulsed and cw molecular beam.