【作者】 刘润琴；

【导师】 印建平；

【作者基本信息】 华东师范大学 ， 光学， 2011， 博士

【摘要】 冷分子在分子光谱、精密测量、分子冷碰撞及冷化学等方面有着非常重要的应用。近十多年来,冷分子的产生及其相关研究吸引了众多的眼球。本文围绕中性分子的激光导引及其连续冷分子束的产生开展理论方案的研究和探索。我们提出了利用空心光子晶体光纤中红失谐的高斯模式导引中性分子的方案。我们基于一个经典模型理论计算了分子的直导引效率和弯曲导引效率,并利用Monte-Carlo方法数值模拟了分子导引的动力学过程,研究了分子的导引效率、导引后分子束的横向和纵向速度分布等。模拟结果与理论计算值吻合得很好。当激光功率为2kW时,I2分子的直导引效率约为24.6%；当激光功率为200W且光纤的曲率半径为0.2cm时,I2分子的弯曲导引效率约为1.2%,并获得了连续的冷分子束。我们提出了利用空芯光纤中红失谐的HE11模S型弯曲导引中性分子束的方案,计算了空芯光纤中I2分子的光学势,并通过数值模拟研究了分子导引效率、导引后分子束的横向和纵向温度与入射激光功率及光纤曲率半径的关系。当入射激光功率为6KW、两弯曲部分的曲率半径为2cm、入射分子束的横向和纵向温度分别为0.5K和5K时,相应的分子导引效率为0-26%。导引后分子束的横向和纵向温度分别为1.9mK和0.5K,出射分子束的束流为108-109s-。我们提出了利用弯曲集成光纤束对中性分子进行全光型速度滤波的新方案,计算了I2分子在双色消逝波场中的光学势,并根据一个经典理论模型计算了分子的导引效率、导引后分子束的横、纵向温度。我们采用经典Monte-Carlo方法模拟了被导引分子的运动轨迹,研究了出射分子束的导引效率、横向和纵向速度和空间分布等。当双色激光功率分别为10W(1064nm)和3.58W(266nm)、波导弯曲半径为R=0.2cm、入射碘分子束的横纵向温度分别为1K和5K时,相应的导引效率为4.1×10-7、导引后分子束的横纵向温度分别为0.29mK和57mK,出射分子束的束流为105-106s-1。我们提出了采用四根平板波导实现分子束的U型弯曲导引及速度滤波的新方案,计算了四根平板波导空心区域的消逝波场分布及碘分子的光学势和总囚禁势,并数值研究了分子的导引效率、导引后分子束的横、纵向温度等。当入射激光功率为200W,弯曲导引段的曲率半径为2cm时,出射分子束的横向和纵向温度分别为340μK和15.3mK,相应的束流为104-105s-1。我们还提出了利用腔增强高斯光束导引中性分子的新方案。当分子束入射方向与腔轴线之间存在一定的夹角时,可以实现对低速分子的速度滤波。我们计算了腔内高斯光束的光场分布及碘分子的光学势,并利用Monte-Carlo方法数值研究了分子的导引效率、导引后分子束的横、纵向温度等。当入射激光的功率为100W,入射束流与腔轴线之间夹角θ=60。时,出射分子束的横向和纵向温度分别为4mK和134mK,相应的束流为108～109s-1。更多还原

【Abstract】 Cold molecules offer new opportunities for molecular spectroscopy, precision measurement, cold collisions, and cold chemistry. Over the decade, there is a great interest in the production of cold molecules and their manipulation. This thesis is dedicated to the theoretical study of laser guiding of neutral molecules and generation of cw cold molecular beams.We propose a promising scheme to guide arbitrary neutral molecules in a hollow-core photonic band gap (HC-PBG) fiber by using a red-detuned Gaussian mode. We theoretically calculate the guiding efficiencies for both the straight guide and bent guide by using a classical model, and study the dynamic behavior of the laser guided molecules by Monte-Carlo simulation. The simulated values for the guiding efficiency, the transverse and longitudinal velocity distributions of the guided molecular beams agree well with those obtained theoretically. When the input laser power is 2kW, the straight guiding efficiency for I2 molecules is about 24.6%. While the input laser power is 200W and the radius of the curvature of the laser fiber is R=0.2cm, the bent guiding efficiency for I2 molecules is about 1.2%, and a cw cold molecular beam will be generated.We propose a novel scheme to bently guide neutral molecules in a hollow optical fiber using a red-detuned HE11 mode. We theoretically calculate the optical potential for I2 molecules inside the hollow fiber and numerically investigate the dependences of the guiding efficiency, the transverse and longitudinal temperatures of guided I2 molecules on both the laser power and the radius of the curvature of the bent guide. Our study shows that and when an input laser is 6kW, and an input I2 molecular beam with a transverse temperature of 0.5K and a longitudinal temperature of 5K is used, a cw cold I2 molecular beam with a transverse temperature of 1.9mK and a longitudinal one of 0.5K will be generated by using a S-shaped hollow optical fiber with a 2cm radius-of- curvature for two bends, and the corresponding guiding efficiency and output flux are about 0.126% and the order of 108～109s-1,respectively.We propose a new scheme to generate a cw cold molecular beam by optically guiding molecules around an S-shaped integrated fiber bundle. We calculate the optical potential for I2 molecules inside the two-color evanescent field around the fiber bundle, and theoretically estimate the guiding efficiency of the guided molecular beam as well as its transverse and longitudinal temperatures based on a classical model. We also perform numerical simulations for the process of guiding molecules through the bent guide, and obtain the guiding efficiency of the output molecular beam as well as its spatial and velocity distributions in both transverse and longitudinal directions. When the power of two input lasers are 10W (1064nm) and 3.58W (266nm), the radius of the curvature of the fiber bundle is 0.2cm, and the transverse and longitudinal temperatures of the input I2 molecular beam are 0.5K and 5K, a cw cold I2 molecular beam with a transverse temperature of 0.29mK and a longitudinal one of 57mK will be produced, and the corresponding guiding efficiency and output flux are about 4.1×10-7 and the order of 105～106s-1,respectively.We propose a U-shaped laser guiding and velocity filtering scheme for cold molecules by using the evanescent waves inside four planar waveguides. We theoretically calculate the distribution of evanescent fields and the optical potential for I2 molecules inside the four planar waveguides, and numerically investigate the final guiding efficiency as well as the transverse and longitudinal temperatures of the guided I2 molecular beam. Our research shows that when the power of each incident laser is 200W, and the curvature radius of the bent guide is 2cm, a cw cold molecular beam with a transverse temperature of 0.34mK and a longitudinal one of 15.3mK can be obtained, and the corresponding output flux is about 104～105s-1We also propose a laser guiding scheme for cold molecules by using a cavity enhanced Gaussian beam. We calculate the light field distribution and the optical potential for I2 molecules inside the optical cavity, and study the dynamic behavior of laser guided molecules by classical Monte-Carlo simulation. Our study shows that when the input laser power is 100W and the angle between the input molecular beam and the axis of the optical cavity isθ=60°, a cw cold molecular beam with a flux of 108～109s-1, a transverse temperature of 4mK and a longitudinal one of 134mK will be generated.更多还原