本文選題：緩沖氣體冷卻 + 靜電速度濾波器��； 參考：《華東師范大學(xué)》2016年博士論文

【摘要】：緩沖氣體冷卻作為一種獲得低溫分子束的技術(shù)手段,被廣泛應(yīng)用于冷分子相關(guān)實(shí)驗(yàn)中。本文介紹了利用靜電斯塔克效應(yīng),在實(shí)驗(yàn)中通過四極靜電導(dǎo)引桿對緩沖氣體冷卻后的極性分子CH3F進(jìn)行操控,并通過調(diào)節(jié)CH3F樣品分子和緩沖氣體He的流量,得到不同束流性質(zhì)的CH3F冷分子束樣品的過程。在通入CH3F樣品分子束流量不變的情況下,通過逐漸增加緩沖氣體流量,發(fā)現(xiàn)了經(jīng)過四極靜電導(dǎo)引桿導(dǎo)引后CH3F分子束信號強(qiáng)度先上升后下降的變化規(guī)律。提出了在高流量緩沖氣體的條件下,導(dǎo)引信號強(qiáng)度隨緩沖氣體流量的增加而下降的理論模型,并解釋了相關(guān)實(shí)驗(yàn)現(xiàn)象。對所創(chuàng)建理論模型進(jìn)行了三維蒙特卡洛模擬,模擬結(jié)果與實(shí)驗(yàn)結(jié)果對照發(fā)現(xiàn),該方法可以用于測量低溫條件下極性分子的轉(zhuǎn)動溫度以及平動碰撞截面與平均轉(zhuǎn)動碰撞截面之比。針對既沒有電偶極矩也沒有磁偶極矩的中性分子,提出了一種通過腔增強(qiáng)效應(yīng)產(chǎn)生高強(qiáng)度紅失諧單頻單模激光束來操控12分子束的全光型速度濾波器和分束器的新方案,并通過三維蒙特卡洛方法對12分子的速度濾波和分束效果進(jìn)行了模擬。通過激光消融的方法產(chǎn)生了用于激光冷卻的MgF自由基,分別通過質(zhì)譜和光譜的方法觀測到了MgF自由基分子的信號。首先,本文介紹了利用靜電斯塔克效應(yīng)操控極性分子的基本原理；利用有限元軟件對實(shí)驗(yàn)所用四極導(dǎo)引桿的電場分布進(jìn)行了模擬,通過蒙特卡洛的方法對分子束在靜電場中的動力學(xué)過程進(jìn)行了理論模擬,得到了分子束的速度分布、空間分布和導(dǎo)引效率。研究了經(jīng)過準(zhǔn)直器后樣品分子束橫向速度以及縱向速度的變化,以及不同轉(zhuǎn)動量子態(tài)的導(dǎo)引效率。介紹了整套實(shí)驗(yàn)裝置,包括真空系統(tǒng)、四極靜電導(dǎo)引電極、脈沖高壓開關(guān)裝置、低溫系統(tǒng)以及四極質(zhì)譜儀分子束探測系統(tǒng)。本文第三章詳細(xì)介紹了通過高壓開關(guān)得到分子束縱向速度分布的基本原理。在早期的實(shí)驗(yàn)裝置中,由于樣品分子管道、真空系統(tǒng)以及銅腔結(jié)構(gòu)設(shè)計(jì)不合理,導(dǎo)致最初的實(shí)驗(yàn)結(jié)果與國際同行的實(shí)驗(yàn)結(jié)果有出入,隨后我們通過仔細(xì)調(diào)研大量文獻(xiàn),找到了問題所在,并針對這些問題對低溫裝置、真空系統(tǒng)以及分子束源系統(tǒng)進(jìn)行了一系列的改進(jìn),實(shí)驗(yàn)測量得到了CH3F冷分子束的信號強(qiáng)度和縱向速度分布,將改進(jìn)前后的實(shí)驗(yàn)結(jié)果進(jìn)行了比較,并就改進(jìn)前后實(shí)驗(yàn)結(jié)果的異同點(diǎn)進(jìn)行了理論分析與討論。通過理論計(jì)算和三維蒙特卡洛的方法對低溫銅腔中CH3F分子與3.5K He原子碰撞后平動溫度和轉(zhuǎn)動溫度的降低進(jìn)行了詳細(xì)的研究,本文第四章詳細(xì)介紹了三維蒙特卡洛模擬的過程。通過模擬結(jié)果與實(shí)驗(yàn)結(jié)果對照,得到了CH3F-He的平動碰撞截面與平均轉(zhuǎn)動碰撞截面之比γ=σr/σr=36.49±6.15。在本文第五章中,為了得到理想的超冷分子束源,針對既沒有電偶極矩也沒有磁偶極矩的中性分子(如12分子和CH4分子等),提出了一種全光型速度濾波器和分束器的新方案。利用ABCD矩陣原理,對所用紅失諧1064nm激光在諧振腔內(nèi)的模式進(jìn)行了理論計(jì)算,基于當(dāng)前現(xiàn)有的實(shí)驗(yàn)條件和激光諧振腔腔增強(qiáng)理論,對諧振腔的腔增強(qiáng)因子進(jìn)行了理論推導(dǎo),同時還調(diào)研了目前市場上滿足實(shí)驗(yàn)條件的激光器。通過自編的Labview程序產(chǎn)生了諧振腔內(nèi)光場分布的數(shù)值矩陣,然后將其導(dǎo)入到c++程序并對分子在光場內(nèi)的動力學(xué)過程進(jìn)行了蒙特卡洛模擬。當(dāng)兩個諧振腔相交夾角為80度的情況下,得到了縱向速度分布半高寬為1m/s的12分子束,相應(yīng)的平動溫度為8mK。在光強(qiáng)不變的情況下,通過調(diào)節(jié)兩個諧振腔相交夾角從80度到10度,得到了1.6%到98.4%的連續(xù)分束比。在相交夾角不變的情況下,通過調(diào)節(jié)兩束光的光強(qiáng)比,得到了10.3%到89.7%的連續(xù)分束比。模擬結(jié)果表明：這種全光型速度濾波器和光學(xué)分束器新方案可用于實(shí)現(xiàn)對中性分子(如12分子CH4分子等)的有效操控。顯然,這樣的超冷12分子束在激光頻率穩(wěn)定和光學(xué)頻標(biāo)中必將有著十分重要的應(yīng)用。激光消融是一種通過固態(tài)樣品制備樣品分子束的常用方法,在本文第六章中采用激光消融MgF2固體藥片的方法,得到了用于激光冷卻的MgF自由基分子束源,分別采用四極質(zhì)譜儀和光電倍增管測量到了室溫下MgF的質(zhì)譜和自發(fā)輻射熒光光譜信號。當(dāng)消融激光的焦點(diǎn)聚焦在樣品上的位置不變時,MgF自由基的信號會在幾分鐘的時間內(nèi)迅速衰減,只有不斷改變激光焦點(diǎn)在樣品上的位置才可以得到穩(wěn)定的MgF自由基分子信號。實(shí)驗(yàn)中我們采用步進(jìn)電機(jī)來帶動反射鏡調(diào)節(jié)旋鈕,得到了長時間的穩(wěn)定產(chǎn)出的MgF自由基質(zhì)譜信號。為了實(shí)現(xiàn)MgF分子的激光冷卻,本文第六章簡單介紹了MgF自由基分子制備的實(shí)驗(yàn)工作。主要包括：MgF2固體樣品的激光消融、MgF自由基分子束的質(zhì)譜和熒光光譜探測方案與結(jié)果等。最后一章為總結(jié)與展望。
[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.
【學(xué)位授予單位】：華東師范大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：O441.1

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