静电和光学速度滤波技术的理论与实验研究

发布时间：2018-05-29 02:47

本文选题：缓冲气体冷却 + 静电速度滤波器　；参考：《华东师范大学》2016年博士论文

【摘要】：缓冲气体冷却作为一种获得低温分子束的技术手段,被广泛应用于冷分子相关实验中。本文介绍了利用静电斯塔克效应,在实验中通过四极静电导引杆对缓冲气体冷却后的极性分子CH3F进行操控,并通过调节CH3F样品分子和缓冲气体He的流量,得到不同束流性质的CH3F冷分子束样品的过程。在通入CH3F样品分子束流量不变的情况下,通过逐渐增加缓冲气体流量,发现了经过四极静电导引杆导引后CH3F分子束信号强度先上升后下降的变化规律。提出了在高流量缓冲气体的条件下,导引信号强度随缓冲气体流量的增加而下降的理论模型,并解释了相关实验现象。对所创建理论模型进行了三维蒙特卡洛模拟,模拟结果与实验结果对照发现,该方法可以用于测量低温条件下极性分子的转动温度以及平动碰撞截面与平均转动碰撞截面之比。针对既没有电偶极矩也没有磁偶极矩的中性分子,提出了一种通过腔增强效应产生高强度红失谐单频单模激光束来操控12分子束的全光型速度滤波器和分束器的新方案,并通过三维蒙特卡洛方法对12分子的速度滤波和分束效果进行了模拟。通过激光消融的方法产生了用于激光冷却的MgF自由基,分别通过质谱和光谱的方法观测到了MgF自由基分子的信号。首先,本文介绍了利用静电斯塔克效应操控极性分子的基本原理；利用有限元软件对实验所用四极导引杆的电场分布进行了模拟,通过蒙特卡洛的方法对分子束在静电场中的动力学过程进行了理论模拟,得到了分子束的速度分布、空间分布和导引效率。研究了经过准直器后样品分子束横向速度以及纵向速度的变化,以及不同转动量子态的导引效率。介绍了整套实验装置,包括真空系统、四极静电导引电极、脉冲高压开关装置、低温系统以及四极质谱仪分子束探测系统。本文第三章详细介绍了通过高压开关得到分子束纵向速度分布的基本原理。在早期的实验装置中,由于样品分子管道、真空系统以及铜腔结构设计不合理,导致最初的实验结果与国际同行的实验结果有出入,随后我们通过仔细调研大量文献,找到了问题所在,并针对这些问题对低温装置、真空系统以及分子束源系统进行了一系列的改进,实验测量得到了CH3F冷分子束的信号强度和纵向速度分布,将改进前后的实验结果进行了比较,并就改进前后实验结果的异同点进行了理论分析与讨论。通过理论计算和三维蒙特卡洛的方法对低温铜腔中CH3F分子与3.5K He原子碰撞后平动温度和转动温度的降低进行了详细的研究,本文第四章详细介绍了三维蒙特卡洛模拟的过程。通过模拟结果与实验结果对照,得到了CH3F-He的平动碰撞截面与平均转动碰撞截面之比γ=σr/σr=36.49±6.15。在本文第五章中,为了得到理想的超冷分子束源,针对既没有电偶极矩也没有磁偶极矩的中性分子(如12分子和CH4分子等),提出了一种全光型速度滤波器和分束器的新方案。利用ABCD矩阵原理,对所用红失谐1064nm激光在谐振腔内的模式进行了理论计算,基于当前现有的实验条件和激光谐振腔腔增强理论,对谐振腔的腔增强因子进行了理论推导,同时还调研了目前市场上满足实验条件的激光器。通过自编的Labview程序产生了谐振腔内光场分布的数值矩阵,然后将其导入到c++程序并对分子在光场内的动力学过程进行了蒙特卡洛模拟。当两个谐振腔相交夹角为80度的情况下,得到了纵向速度分布半高宽为1m/s的12分子束,相应的平动温度为8mK。在光强不变的情况下,通过调节两个谐振腔相交夹角从80度到10度,得到了1.6%到98.4%的连续分束比。在相交夹角不变的情况下,通过调节两束光的光强比,得到了10.3%到89.7%的连续分束比。模拟结果表明：这种全光型速度滤波器和光学分束器新方案可用于实现对中性分子(如12分子CH4分子等)的有效操控。显然,这样的超冷12分子束在激光频率稳定和光学频标中必将有着十分重要的应用。激光消融是一种通过固态样品制备样品分子束的常用方法,在本文第六章中采用激光消融MgF2固体药片的方法,得到了用于激光冷却的MgF自由基分子束源,分别采用四极质谱仪和光电倍增管测量到了室温下MgF的质谱和自发辐射荧光光谱信号。当消融激光的焦点聚焦在样品上的位置不变时,MgF自由基的信号会在几分钟的时间内迅速衰减,只有不断改变激光焦点在样品上的位置才可以得到稳定的MgF自由基分子信号。实验中我们采用步进电机来带动反射镜调节旋钮,得到了长时间的稳定产出的MgF自由基质谱信号。为了实现MgF分子的激光冷却,本文第六章简单介绍了MgF自由基分子制备的实验工作。主要包括：MgF2固体样品的激光消融、MgF自由基分子束的质谱和荧光光谱探测方案与结果等。最后一章为总结与展望。
[Abstract]:As a technical means of obtaining the low temperature molecular beam, the buffer gas cooling is widely used in the cold molecular correlation experiment. This paper introduces the use of the electrostatic stac effect in the experiment to manipulate the polar molecule CH3F after the cooling of the buffer gas by the quadrupole electrostatic guide rod, and by adjusting the CH3F sample molecule and the buffer gas He. The process of CH3F cold molecular beam samples with different beam properties is obtained. In the case of the constant flow of the molecular beam of the CH3F sample, the change law of the CH3F molecular beam signal intensity is found after the gradual increase of the flow of the buffer gas, and the bar of the high flow buffer gas is put forward. The theoretical model of the intensity of the guide signal decreases with the increase of the flow of the buffer gas, and the related experimental phenomena are explained. A three-dimensional Monte Carlo simulation of the theoretical model is carried out. The simulation results are compared with the experimental results. This method can be used to measure the rotation temperature of the lower polar molecules and the translational collision intercepting of the low temperature strip. The ratio of the surface to the average rotational collision section. For the neutral molecules with neither the electric couple moment nor the magnetic dipole moment, a new scheme of the full optical velocity filter and beam splitter of the 12 molecular beam by the enhancement effect of the cavity is proposed to produce the high intensity red Unharmonic single frequency single mode laser beam, and the 12 molecule is used by the three dimensional Monte Carlo method. The velocity filtering and beam splitting effect were simulated. The MgF free radicals used for laser cooling were produced by laser ablation. The signals of the MgF radicals were observed by mass spectrometry and spectra. First, the basic principle of using the electrostatic stac effect to manipulate polar molecules was introduced; the finite element software was used. The electric field distribution of the quadrupole guide rod used in the experiment is simulated. The kinetic process of the molecular beam in the electrostatic field is simulated by Monte Carlo method. The velocity distribution, the spatial distribution and the guidance efficiency of the molecular beam are obtained. The changes of the transverse velocity and the longitudinal velocity of the molecular beam after the collimator are studied. As well as the guidance efficiency of different rotational quantum states, the whole set of experimental devices, including vacuum system, quadrupole electrostatic guide electrode, pulse high voltage switch device, low temperature system and quadrupole mass spectrometer molecular beam detection system, is introduced in this paper. The third chapter introduces the basic principle of obtaining the longitudinal velocity distribution of the molecular beam through high voltage switch. Due to the unreasonable design of the sample molecular pipeline, the vacuum system and the copper cavity structure, the initial experimental results are different from those of the international counterparts. Then we find out the problems by careful investigation of a large number of documents, and for these questions to the cryogenic device, the vacuum system and the molecular beam source system. A series of improvements were carried out. The signal intensity and the longitudinal velocity distribution of the CH3F cold molecular beam were measured. The experimental results before and after the improvement were compared, and the similarities and differences of the experimental results before and after the improvement were theoretically analyzed and discussed. The CH3F molecules in the low temperature copper cavity were calculated by theoretical calculation and three dimensional Monte Carlo method. The reduction of translational temperature and rotational temperature after 3.5K He atom collisions is studied in detail. The fourth chapter of this paper introduces the process of three-dimensional Monte Carlo simulation in detail. By comparing the simulation results with the experimental results, the ratio of the translational cross section of the CH3F-He to the average rotational collision cross section is obtained. The ratio of gamma = Sigma r/ Sigma r=36.49 + 6.15. to the average rotation collision cross section is obtained in this paper. In order to obtain an ideal supercooled molecular beam source, a new scheme of all optical velocity filter and beam splitter is proposed for neutral molecules, such as 12 molecules and CH4 molecules, which have neither dipole moment nor magnetic dipole moment. The theory of ABCD matrix principle is used to calculate the mode of the red detuning 1064nm laser in the resonant cavity. Based on the current experimental conditions and the laser resonator cavity enhancement theory, the cavity enhancement factor of the resonator is theoretically derived. At the same time, the laser which satisfies the experimental conditions in the market is also investigated. The numerical matrix of the optical field distribution in the resonant cavity is produced by the self compiled Labview program, and then it is introduced into the c++ program and The Monte Carlo simulation of the kinetic process in the optical field is carried out. When the intersection angle of the two resonators is 80 degrees, the 12 molecular beam with a half width of 1m/s in the longitudinal velocity distribution is obtained. The corresponding translational temperature is 8mK. and the angle of the intersection of two resonators from 80 degrees to 10 degrees is obtained by adjusting the angle of the intersection from 80 to 10. The continuous beam splitting ratio of 6% to 98.4%. The continuous beam splitting ratio of 10.3% to 89.7% by adjusting the intensity ratio of two beams of light is obtained by adjusting the light intensity ratio of the two beams. The simulation results show that the full optical speed filter and the new optical beam splitter scheme can be used to effectively control the neutral molecules (such as the 12 molecule CH4 molecule, etc.). The supercooled 12 molecular beams are bound to be very important in laser frequency stabilization and optical frequency calibration. Laser ablation is a common method for the preparation of sample molecular beams through solid samples. In the sixth chapter, the laser ablation of MgF2 solid tablets is used to obtain the MgF free radical molecular beam source used for laser cooling. A quadrupole mass spectrometer and a photomultiplier are used to measure the MgF mass spectra and spontaneous emission fluorescence spectra at room temperature. When the focus of the ablation laser focuses on the sample position, the signal of the MgF free radical is rapidly attenuated for a few minutes, and only the constant change of the focal point on the sample can be stabilized. The MgF free radical molecular signal is fixed. In the experiment, we use the stepper motor to drive the reflector to adjust the knob and obtain a long time stable MgF free radical mass spectrum signal. In order to realize the laser cooling of the MgF molecules, the sixth chapter briefly introduces the experimental work on the preparation of the MgF free radicals. It mainly includes the MgF2 solid sample. Laser ablation, MgF free radical molecular beam mass spectrometry and fluorescence spectrum detection scheme and results. The last chapter is the summary and prospect.
【学位授予单位】：华东师范大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O441.1

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