Theoretical Studies On Optical Stark Deceleration And Reflection For Neutral Molecules

In recent years,cooling,trapping and manipulation of neutral molecules has become one of hot points in the frontiers of physical research.Compared with cold atoms,neutral molecules have much richer internal states.As a result,cold molecules or ultracold molecules can be widely used in basic researches of the fundamental physical questions,the precision measurements of fundamental physical constants, studies of cold molecular collisions,quantum computing and information processing as well as ultracold chemistry,and so on.So the study of molecule optics has very important scientific significance and wide application prospects.During the past decade,the study of generation and application of cold molecules has obtained many fast development and important progress.In this thesis,the principle,experiments and recent progress on cooling,trapping and manipulating of neutral molecules have been first briefly introduced and reviewed.Secondly,we have briefly reviewed two kinds of molecular beams:a pulsed supersonic beam and a cw effusive molecular beam. Thirdly,some theoretical researches on optical Stark deceleration for neutral molecules are performed.Afterwards,a novel molecular mirror with a semi-Gaussian laser beam is proposed.In final,our research work is summarized and the future investigation is briefly looked ahead.We propose a new experimental scheme to generate a semi-Gaussian laser beam (SGB)without any diffracted fringes.We employ a spatial light modulator to decrease coherence of Gaussian laser beam,and let this modulated laser beam pass through a blade,and then we obtain a SGB without any diffracted fringes.Using statistic optics and Fresnel diffraction theory,we calculate the intensity distribution of the generated SGB.We propose two kinds of optical Stark decelerators for neutral molecules using a SGB:a single-satge optical Stark decelerator for a cw molecular beam with a single quasi-cw SGB,and a multistage optical Stark decelerator for a pulsed molecular beam in an electrostatic storage ring with a quasi-cw SGB.With Monte-Carlo method,we study the deceleration effect of optical Stark decelerator and our results show that we can obtain a ND₃ molecular beam with a relative average kinetic-energy loss of about 10%and a relative output molecular number of more than 90%by using a single quasi-cw SGB with a maximum optical well depth of 7.33mK.When the molecular beam is trapped in an electrostatic storage ring,the SGB can decelerate molecular beam for many times and the deceleration effect is accumulated.Monte-Carlo simulated results show that deuterated ammonia molecules with a mean velocity of 15m/s trapped in the electrostatic storage ring are decelerated to 2.89m/s after interacting with a SGB whose depth is 10.86mK for 24 times.We propose a novel optical Stark decelerator to slow and trap an arbitrary pulsed molecular beam using a stationary quasi-cw red-detuned optical lattice.Monte-Carlo simulated results show that a methane supersonic beam can be decelerated from 230m/s to zero by such optical lattice with a length of only several mm,which can used to trap decelerated molecular sample with a sub-mK temperature.Also,we study the dependence of the deceleration effect on the position of the synchronous molecules and deceleration stages number.We propose two novel all-optical molecular mirrors for neutral molecules with a pulsed red-detuned SGB and a cw blue-detuned SGB,which pave the way to the studies of geometric molecule optics and wave molecule optics.Monte-Carlo simulated results show that cw blue-detuned SGB mirror can be used to realize specular reflection of 58.2%iodine molecules in an incident molecular beam with a temperature of 30mK when the semi-Gaussian laser power is 1.0kW.In the case of the pulsed red-detuned SGB mirror,an electrostatic Stark-decelerated molecular beam can be reflected by the pulsed SGB mirror with suitable parameters.We also study the dependence of the reflection efficiency on the parameters of the SGB mirror and the incident molecular beam.Results show that the higher the laser power is,the lower the velocity of the incident molecular beam is,the higher the reflection efficiency is.