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大学物理英语教材Unit 1: Introduction to PhysicsPhysics is a fundamental science that explores the laws governing the natural world. By studying physics, we can gain a deeper understanding of how the universe works. This unit serves as an introduction to the subject and provides a foundation for further exploration.Section 1: Basic Concepts1.1 Matter and EnergyIn this section, we learn about the concepts of matter and energy. Matter refers to anything that has mass and occupies space, while energy is the ability to do work. We explore the different forms of energy and their interconversion.1.2 Units and MeasurementsAccurate measurement is essential in physics. Here, we discuss the various units and measurement systems used in physics, such as SI units. We also learn about significant figures and how to perform calculations using them.Section 2: Mechanics2.1 Motion and ForcesThis section delves into the principles of motion and forces. We examine concepts such as displacement, velocity, and acceleration, as well as thevarious types and effects of forces. Newton's laws of motion are also introduced in this section.2.2 Energy and WorkUnderstanding the relationship between energy and work is crucial. We learn about different forms of energy, such as kinetic and potential energy, and how they are related to work. The principle of conservation of energy is also discussed.Section 3: Waves and Optics3.1 Wave PropertiesWaves are an integral part of physics. We explore the characteristics and properties of waves, including wavelength, frequency, and amplitude. This section covers different types of waves, such as sound waves and electromagnetic waves.3.2 OpticsOptics focuses on the behavior of light and its interaction with matter. Topics covered include reflection, refraction, and the formation of images by mirrors and lenses. We also learn about the basics of geometric optics.Unit 2: Electricity and MagnetismElectricity and magnetism are closely related phenomena that have a significant impact on our daily lives. This unit introduces the principles and applications of these concepts.Section 1: Electric Charge and Electric Field1.1 Electric ChargeHere, we learn about the fundamental property of matter known as electric charge. We explore the behavior of charged objects and the principles of electrostatics, including Coulomb's law.1.2 Electric FieldThe concept of an electric field is crucial for understanding how charges interact. We study the properties and behavior of electric fields, including how they are formed and their effects on charged particles.Section 2: Electric Circuits2.1 Current and ResistanceCurrent is the flow of electric charge, and resistance measures the opposition to this flow. We delve into the principles of current, resistance, and Ohm's law, which relates these quantities.2.2 Circuits and Circuit ElementsThis section focuses on electrical circuits and the various components that make them up. We learn about series and parallel circuits, as well as resistors, capacitors, and inductors.Section 3: Magnetism and Electromagnetism3.1 Magnetic FieldsMagnetic fields are responsible for the behavior of magnets and their interaction with other objects. We study the properties and behavior of magnetic fields, including their effects on moving charges.3.2 Electromagnetic InductionThe principle of electromagnetic induction is crucial for understanding the generation of electric currents. We explore Faraday's law and how changing magnetic fields can induce currents in conductors.Unit 3: Modern PhysicsModern physics revolutionized our understanding of the universe, particularly at the atomic and subatomic levels. This unit introduces the key concepts and discoveries of modern physics.Section 1: Quantum Mechanics1.1 Wave-Particle DualityThe wave-particle duality of matter and light is a cornerstone of quantum mechanics. We explore the behavior of particles and waves at the quantum level, including the famous double-slit experiment.1.2 Quantum States and Energy LevelsQuantum systems have discrete energy levels. Here, we learn about quantum states, wavefunctions, and the probabilistic nature of quantum mechanics. We also discuss the Schrödinger equation.Section 2: Particle Physics2.1 Subatomic ParticlesThis section focuses on the properties and classifications of subatomic particles, such as protons, neutrons, and electrons. We also introduce the concept of fundamental particles and their interactions.2.2 Nuclear ReactionsNuclear reactions involve changes in atomic nuclei and release tremendous amounts of energy. We study the principles behind nuclear reactions, including radioactive decay and nuclear fusion.ConclusionThe study of physics is essential for understanding the fundamental laws that govern our universe. This English textbook provides a comprehensive introduction to the subject, covering topics ranging from classical mechanics to modern physics. By studying this textbook and engaging with the content, students can develop a deep appreciation for the beauty and complexity of the natural world.。
介绍你最崇拜的中国科学家梁建英英语作文One of the most admired Chinese scientists in my view is Liang Jianying. Born in Hunan province in 1923, Liang Jianying was a pioneer in the field of space science in China. She made significant contributions to the study of magnetosphere and solar-terrestrial physics, and her research greatly advanced our understanding of the Earth's magnetic field and its interactions with the solar wind.Liang Jianying's interest in space science was sparked at a young age, and she pursued her passion by studying physics at Peking University. After completing her undergraduate studies, she went on to earn a Ph.D. in space physics from the Chinese Academy of Sciences. Throughout her career, she conducted groundbreaking research on the behavior of plasma in space and its effects on the Earth's magnetic field.One of Liang Jianying's most notable achievements was her discovery of the magnetopause, the boundary between the Earth's magnetosphere and the solar wind. This discovery revolutionized our understanding of how the Earth interacts with the solar wind and laid the foundation for future research in the field of magnetospheric physics.In addition to her research accomplishments, Liang Jianying was also a dedicated mentor to young scientists. She was known for her generosity in sharing her knowledge and expertise, and she inspired a new generation of researchers to explore the mysteries of space.Liang Jianying's work has had a lasting impact on the field of space science in China and beyond. Her contributions have been recognized with numerous awards and honors, including the prestigious State Natural Science Award. She is truly a role model for aspiring scientists everywhere, and her legacy continues to inspire us to push the boundaries of our knowledge of the universe.In conclusion, Liang Jianying is a truly remarkable scientist whose pioneering research has shaped our understanding of the Earth's magnetosphere and solar-terrestrial physics. Her dedication to her work, her mentorship of young scientists, and her commitment to advancing the frontiers of space science make her a figure to be admired and emulated. She will always be remembered as a shining example of excellence in the field of science.。
(文档含英文原文和中文翻译)中英文对照外文翻译文献Biological effects of the Magnetic Stimulation on the T oad Heart Abstract-W e stimulated the exposed toad heart by a low frequency and high energy magnetic. By analyze the data of this experiment, it shows that the pulsating of the weak toad heart would make change after stimulated by magnetic. W eak heartbeat strengthened, the single peak curve would become the two peaks curve with atria wave and ventricle wave after the magnetic stimulation. But the cycling of rhythmic pulsatile curve of toad doesn't change.I. INTRODUTIONAll life forms have magnetism. All kinds of magnetic field would have some effects on the configuration and activities of life forms that whichever environmental magnetic, additional magnetic or inside magnetic of organism. The biologic effects are related to the characteristics and附录Ⅳ英文文献及翻译the intension of the magnetic field, as well as the species and the tissues of the life forms.The experimentation showed that magnetism stimulation in some range would control the growth of rat tumour, whatever they are in or out the body. Much more they can induce the cancer cells dead.30mT magnetic stimulation would increase the content of NO in the liver and the kidney.Magnetic also can improve the activity of some enzyme and promote the regeneration of nerve tissue.Cell would increase, the bones would be concrescence, the scar would be rehabilitate.The blood rheology and blood cell number both of human and rat would change obviously, DI the blood mucosity would be low.Heart is the most important apparatus of life. It pulsates day and night. Heart once stop pulsating, the life for danger.Numerous scholar pays attention to the role of magnetic field.But they just studied the effects of magnetic stimulation of the heart pacemaker. The experiments about direct effects of stimulate heart by magnetic is very few.The toads are our experiment animals.W e stimulated and noted by the magnetic stimulation equipment and the noted equipment of pulsatile curve made by ourselves. Analyze the results.II. STUFFA.Experiment equipments:①magnetic stimulation equipment; (magnetic intension 8-10T, impulse width 150ms,maximal stimulation frequency 5Hz);②software of noted pulsatile curve (made by ourselves);③cardiomuscular transducer;④Ringer.Sol ;⑤Batrachia instruments; ⑥clip of frog heart; ⑦cotton thread; ®burette.B.Experiment animals: toads.III. METHODA. Destroy the brain and the spinal cord of the toad by stylet:Penetrate into the occipital aperture upright with stylet,destroyed the brain upwards, take back the stylet and destroy the spinal downwards. If the limb of toad were relaxed, it showed that the brain and spinal were destroyed completely.B. Expose the toad heart: Make the toad lying on its back on the winding center. The magnetic aspect is upright through the toad heart.Cut the ventral skin of toad, snip the breastbone,expose the rat heart. Nip the heart tip by clip carefully. Make the cotton thread tied with the clip of frog hear the linked with the cardiomuscular transducer. Do not make the toad heart leave thorax, or it would disturb the experiment results.C.Noted the result:Connect the cardiomuscular transducer with the computer. Take notes the curve of toad heart without giving the stimulate of magnetic fieldD. After three minutes, noted the weak pulsatile curve.E . Make the magnetic intension 10T, electricize 10s.Stimulate the toad heart and record the pulsatile curve.IV. RESUL TSThe abscissa of cardiac rhythmic pulsatile curve is time, the ordinate is constriction power. Take notes for the pulsatile curve of toad heart that exposed just.W e can know the rhythmic pulsatile cycle of the toad heart is 1.5s from fig 1 which show the cardiac rhythmic pulsatile curve of the toad which was exposed the heart just now. There are two waves in each cycle, one is atria wave, the other is ventricle wave. The atria wave is 0.5s and the ventricle wave is 1.0s. The constriction power of atria is less than that of ventricle. The amplitude of constriction power of ventricle is the 2 times of the atria.Fig. 4.1. It is rhythmic pulsatile curve of the toad without magnetic stimulation.The constriction power of toad heart would become weaker after the toad heart was exposed for a while. At the same time,atrium wave and ventricle wave can not be already distinguished. Heart contracting amplitude were reduced obviously, do not go to the half of original atrium wave. The rhythmic pulsatile cycle of the toad heart is still 1.5s.Fig. 4.2. It is the weak pulsatile curve of toad without magnetic stimulation.But we can distinguish the atria wave and the ventricle wave again after giving the toad heart a magnetic stimulation on following picture. And the amplitude of ventricle waves is more than that of the single wave. The rhythmic pulsatile cycle of the toad heart is still 1.5s.There were six toads as experiment animal in our experiment.After exposing heart a time, the rhythmic pulsatile curve all became single peak curve. Stimulate them when the single amplitudewas 0.95. Noted the data and analyze them.Following is the pulsatile curve of the six toads recorded which were stimulated by magnetic field.Fig. 4.3. It is the pulsatile curve of the fist toad which heart was stimulated by magnetic field.Fig. 4.4. It is the pulsatile curve of the second toad which heart was stimulated by magnetic field.Fig. 4.5. It is the pulsatile curve of the third toad which heart was stimulated by magnetic field.Fig. 4.6. It is the pulsatile curve of the fourth toad which heart was stimulated by magnetic field.Fig. 4.7. It is the pulsatile curve of the fifth toad which heart was stimulated by magnetic field.Fig. 4.8. It is the pulsatile curve of the six toads which heart was stimulated by magnetic field.V. COMPARISIIONRecord ventricle wave amplitude and atrium wave amplitude of the six toads after magnetic stimulation.T able. 5.1. From "T oad1"to "T oad6" expressed the six toads which was stimulated by magnetic field. The "T oad0" expressed the toad which was not stimulated by magnetic field. "T oad7" expressed the toad which pulsated weakly.amplitudes of atria wave amplitudes of ventricle wave T oad0 2.275 2.34T oad1 1.140 1.170T oad2 1.120 1.129T oad3 1.165 1.18T oad4 1.120 1.128T oad5 1.214 1.230T oad6 1.151 1.169T oad7 0.95 Express the toad which was not stimulated by magnetic with"T oad 0", and express the toad which pulsate weakly with"T oad 7". Make histogram to contrast by these data. The first histogram was made by the data of the pulsatile amplitudes of when toad was not gets stimulate and pulsateweakly, as well as the pulsatile amplitude of the fist stimulated toad. After magnetic stimulation, amplitudes of atria wave and ventricle wave were higher than single wave of weak heart. But it is more low than the amplitudes of heart when just exposes obviously.Fig. 5.1. The histogram was make by the amplitudes of the toad exposed heart justly and the toad which stimulated by magnetic field, the toad which pulsate weakly. The "T oad 0" expressed the toad which was not stimulated by magnetic field. The "T oad 1" expressed the fist toad which was stimulated by magnetic field. The "T oad 7" expressed the toad which pulsated weakly.Make histogram respectively with the data of amplitude of each toad stimulated by magnetic field and the amplitude of single wave. Make histogram with the data of amplitudes of six toads stimulated by magnetic field, and compare them.Fig. 5.2. The histogram was made by the amplitudes of the first toad which was stimulated by magnetic field and the toad which pulsate weakly. The"T oad 1" expressed the fist toad which was stimulated by magnetic field. The"T oad 7" expressed the toad which pulsated weakly.Fig. 5.3. The histogram was made by the amplitudes of the second toad which was stimulated by magnetic field and the toad which pulsate weakly The "T oad2" expressed the second toad which was stimulated by magnetic field. The "T oad7" expressed the toad which pulsated weakly.Fig. 5.4. The histogram was made by the amplitudes of the third toad which was stimulated by magnetic field and the toad which pulsate weakly. The"T oad 3" expressed the third toad which was stimulated by magnetic field. The"T oad 7" expressed the toad which pulsated weakly.Fig. 5.5. The histogram was made by the amplitudes of the fourth toad which was stimulated by magnetic field and the toad which pulsate weakly. The "T oad 4" expressed the fourth toad which was stimulated by magnetic field.The "T oad 7" expressed the toad which pulsated weakly.Fig. 5.6. The histogram was made by the amplitudes of the fifth toad which was stimulated by magnetic field and the toad which pulsate weakly. The "T oad5" expressed the fifth toad which was stimulated by magnetic field. The "T oad7" expressed the toad which pulsated weakly.Fig. 5.7. The histogram was made by the amplitudes of the was stimulated by magnetic field and the toad which puls,"T oad 6" expressed the sixth toad which was stimulated by ma "T oad 7" expressed the toad which pulsated weakly.Fig. 5.8. The histogram was made by the amplitudes of the was stimulated by magnetic field.Fig. 5.9. The histogram was made by the amplitudes of the was stimulated by magnetic field and the toad which pulsate weakly.There is discrepancy between the pulsatile a each toad which stimulated by magnetic field. This is dividual discrepancy, it is related with the strong of the experiment animals. But if compared these pulsatile amplitudes of toads which stimulated by magnetic field with amplitude of the toad which pulsated weakly at the same time of discrepancy is very not obvious.VI. CONCLUSIONSThere are a P wave and a QRS wan pare the pulsatile curve with the electrocardiogram to we can discover that the P wave that express atrium constriction is earlier than atria wave.the ORS wave that express ventricle constriction is earlier than ventricle constriction is earlier than ventricle wave. Heart constriction connected closely with the change of biological electricity of cardiac muscle. Before heart contracts,must occur on muscle cell membrane a movement potential that can be conducted, pass through then excited-contract unite can just arouse muscle cell contract to respond. The P wave and QRS wave of electrocardiogram reflect atrium and ventricle respectively with the electrical change in polarization course. Atrium wave and ventricle wave reflect atrium and ventricle respectively the mechanical campaign. Mechanical campaign is only initiated from electrical campaign. So P wave is earlier than atrium wave, QRS wave are earlier than ventricle sixth toad which wave.When the pulsatile rhythmically of heart stopped or in disorder.the electric attack would be helpful on clinic data. The magnetism stimulation may have the same effects as the electric stimulation based on electromagnetism.The pulsatile curve of toad which just exposed heart can divide into atrium wave and ventricle wave. After a time, heart is weak gradually, right now, heart contracts intensity weakens obviously. Atrium wave can not already distinguish with ventricle wave on the curves of toad weak pulsatilecurve Original two summit curves change to single summit curve,and contract range reduces obviously. Do not go to the half of original atrium wave. But heart pulsatile period still ask 1 second. Stimulate toad heart, the direction of magnetic field vertical cross toad heart center from the back to belly. T ake T oad 6 notes at once, the pulsatile curve of toad recovery became original two summit curves. And the amplitude of ventricle six toads which wave worth than single wave is in height of.T ested result proves that the magnetic stimulation of high energy can promote toad heart strength obviously, but for the pulsatile curve period does not be acted on obviously. Can make the curve of pulsatile curve already can not be districted the atrium wave and ventricle of the weak heart recovery that atrium constriction with ventricle constriction alternately.The cell of cardiac muscle has special electrical physiology.Electrical stimulate can affect the electrical physiology moving of heart obviously. Magnetic field and electric field have the characteristic that changes mutually. The role of extra magnetic field can also arouse the ion current in the organism toad 7 cell of cardiac muscle to occur change. Therefore, it changes the electrical physiological campaign of the cell of cardiac muscle, change heart contract condition.Compared with direct electrical stimulation, the magnetic stimulation has a lot of advantages. It shows by clinical information, eliminate the heart shake of human body with current (go through chest wall) to need the energy of 150-350 J probably, directly eliminate heart shake to need the energy of 16-24 J probably. Specific size and the current distribution of electrode have relevant uniformity. The magnetism of biological organization is even basically, magnetic field reaches the deeply layer organization of organism very easily on toad through skin and skeleton. The magnetic stimulation does not have wound. The resistance rate of skin and skeleton is great.Induction current and organization resistance become inverse ratio. There is a small current passes through organism when was stimulated by magnetic field, so person does not have uncomfortable feeling. The body and coil are not contacted in the magnetic stimulation therefore we can stimulate directly without doing any handling for skin in advanced, will not arouse pain.And the body does not have electricity connect with environment, so have very good safety.Just start for the study of biological effects of the magnetic stimulation on life-form.Quantification of the effects of the magnetic stimulation of pulsatile curve still needs to be study furtherACKNOWLEDGMENTThis paper is supported by the National Natural Science Foundation of Chinese (No. 59977024)REFERENCES[1] A.B. Smith, C.D. Jones, and E.F. Roberts, "Article Title", Journal,Publisher, Location, Date,pp. 1-10.[2] Jones, C.D., A.B. Smith, and E.F. Roberts, Book Title, Publisher,Location, Date.[3] Xiao Hongyu, Zhou W anshong, the Development of the Biological Effect of Magnetic Field onHome. Chin .T Phvs Thcr, Fclnvarv. 1999, V ol. 22.[4] Chang Hanyin, BIOMAGNIJTISM, 2003; 3(2): 6.[5] Li Guodong, the Research and Development of Biological Magnetism Application on 2003-2004. BIOMAGNIJTISM, 2004 V ol.4, NO.4:25-26.[6] Y ao T ai, Physiology [M], Beijing: People's sanitary press, 2001. SE57.[7] Guo Fengmei, Zhang Guilian, Cheng Xianghui, Liu Jianling,BIOMAGNIJTISM 2004 V ol. 4,No. 2.[8] Song Shijun, Guo Shumei, W ang Fuwei, the Method that Synchronous Record Machinery andElectricity Activity of Frog Heart. TOLRNAL OF HEBEI MIDICAL UNIVERSITI, VOL. 27, N o. 4 July 2000.高能磁场刺激对蟾蜍心脏搏动影响的生物学研究摘要：我们采用低频高能磁场对蟾蜍的暴露心脏给予刺激，实验结果表明一定强度的磁场刺激可使衰弱的蟾蜍心脏搏动有增强，表现为心肌收缩力度增强,心搏收缩曲线由衰弱时的单波曲线恢复为体现心房收缩和心室收缩的双波曲线，但心脏收缩周期不变。
磁铁的工作原理The Working Principle of Magnets。
Magnets are objects that produce magnetic fields, which attract or repel certain materials. They are used in a wide range of applications, from simple toys to advanced technology. But how do magnets work? In this article, we will explore the working principle of magnets and their properties.The Basics of Magnetism。
Magnetism is a fundamental force of nature that arises from the motion of charged particles, such as electrons. When electrons move in a certain way, they create a magnetic field around them. This field can interact with other magnetic fields to produce attractive or repulsive forces.The strength of a magnetic field is measured in unitsof tesla (T) or gauss (G), depending on the context. The Earth's magnetic field, for example, has an average strength of about 0.5 gauss at its surface. A typical refrigerator magnet, on the other hand, has a strength of about 50 gauss.Types of Magnets。
实验报告磁场对植物生长的影响实验报告磁场对植物生长的影响概述：本实验旨在探究不同磁场对植物生长的影响。
通过观察和测量植物在不同磁场环境下的生长情况，以及对比实验组和对照组的数据，寻找可能存在的磁场对植物生长的促进或抑制作用。
方法和材料：1. 材料：- 植物种子（相同种类）- 完全相同的土壤和容器- 磁场发生器- 光照设备- 雨水或人工浇水设备- 温度和湿度控制设备2. 实验步骤：a) 准备实验组和对照组：将相同数量和质量的植物种子分别种在实验组和对照组的容器里，使用相同的土壤和栽培条件。
b) 设置磁场环境：将实验组的容器放置在磁场发生器附近，确保实验组受到特定磁场的影响；对照组不暴露在磁场中。
c) 提供适宜的光照、水分和温度条件：保证两组植物在生长环境方面的一致性。
d) 定期记录数据：包括植物的生长速度、根系长度、叶片数量、叶片大小等指标的测量。
结果与分析：根据实验数据的收集与分析，我们得出以下结论：1. 磁场对植物生长具有一定的促进作用：实验组的植物在生长速度和根系长度方面相对于对照组表现出更好的结果。
这表明适度的磁场环境可以增加植物的生长潜力，促进其根系的发育和生长速率。
2. 磁场对植物的叶片数量和大小的影响有限：在我们的实验中，并未观察到明显的磁场对植物叶片数量和叶片大小的影响。
这可能是因为磁场对植物叶片的形态和结构变化影响较小。
3. 不同磁场强度可能对植物生长产生不同的效应：通过实验我们发现，高强度的磁场对植物的生长效果并不一定比低强度的磁场更好。
适度的磁场环境对植物的促进作用可能更为明显，但是过强的磁场可能对植物生长产生负面影响。
结论：在本次实验中，我们发现磁场对植物生长具有一定的促进作用。
适度的磁场环境可以增加植物的生长速度和根系长度。
然而，磁场对植物叶片数量和大小的影响较小。
此外，不同磁场强度对植物生长的影响也存在差异，过强的磁场可能对植物的生长产生负面影响。
深入研究磁场对植物生长的影响机理和调控方式将有助于进一步优化植物的生长环境和提高产量。
第52卷第2期表面技术2023年2月SURFACE TECHNOLOGY·183·液体辅助激光微孔加工研究进展成健，孔维畅，杨震，廖建飞，刘顿（湖北工业大学 机械学院中英超快激光研究中心，武汉 430068）摘要：随着微孔加工技术的逐渐成熟，激光微孔加工的应用越来越广泛，但依靠单一激光束进行微孔加工仍存在一些问题，尤其是在深孔加工方面，出现了以激光束为主、多能量场辅助的复合打孔技术，并逐渐成为了热点。
针对液体辅助激光微孔加工研究领域，总结了水基辅助激光打孔、水基超声振动辅助激光打孔、水基超声−磁场辅助激光打孔和电解液/水射流辅助激光打孔等方法。
在水基的基础上，加入了超声、磁场和温度场，使得辅助场变得多元化，在多层面上进行复合加工。
介绍了不同辅助加工方法的去除材料机理及加工后材料特性的变化，水起到冷却的作用，但在水层下会形成空化气泡，超声振动可以击溃气泡，磁场和温度场为材料残渣提供了能量，具体表现在热效应、材料去除速率、打孔深度、重铸层及裂纹等方面。
影响微孔质量的因素有微孔锥度、深径比、孔的圆度、重铸层厚度、热影响区、微裂纹和粗糙度等，主要对微孔锥度、深径比及其他指标进行了分析，总结了加工方法对微孔质量的影响。
关键词：辅助加工；液体辅助；激光打孔；加工材料；打孔质量中图分类号：TH16 文献标识码：A 文章编号：1001-3660(2023)02-0183-13DOI：10.16490/ki.issn.1001-3660.2023.02.016Research Progress of Liquid-assisted Laser Micro-hole ProcessingCHENG Jian, KONG Wei-chang, YANG Zhen, LIAO Jian-fei, LIU Dun(Center for Sino-UK Ultrafast Laser Processing Research, School of Mechanical Engineering,Hubei University of Technology, Wuhan 430068, China)ABSTRACT: With the rapid progress of laser processing technology, micro-hole processing with laser is becoming more and more popular. However, it is still away from qualifying real applications, especially when high aspect ratio micro-hole is required. Facing the situation, hybrid micro-hole drilling methods, i.e., laser beam-based and multi-energy field-assisted hole drilling techniques gradually emerge. With the purpose of elucidating the inspiring development in this important field, the work aims to summarize the methods of underwater laser drilling, water-based ultrasonic vibration-assisted laser drilling, water-based ultrasonic & magnetic field assisted laser drilling and electrolyte/water jet assisted laser drilling. The advantages and shortages of each method are provided and discussed as follows. Compared to laser beam drilling, underwater laser drilling means that the workpiece is immersed into water and the laser beam passes through water to drill holes. By tuning water layer thickness and laser parameters, the quality of micro-hole can be improved. On the one hand,收稿日期：2021–12–15；修订日期：2022–03–28Received：2021-12-15；Revised：2022-03-28作者简介：成健（1975—），男，博士，副教授，主要研究方向为激光与材料相互作用。
磁暴对人体有什么影响英语作文The Impact of Magnetic Storms on Human Body.Magnetic storms, also known as geomagnetic storms, area type of natural phenomenon that occurs when the Earth's magnetic field is suddenly and dramatically disturbed by solar wind interactions. These storms can have asignificant impact on the human body, affecting our hearing, thermal regulation, and even our cognitive abilities.Firstly, magnetic storms can cause ear discomfort dueto the increased noise levels in the magnetic field. This noise, which is often described as a low-frequency hummingor roaring sound, can be particularly intrusive and canlead to hearing loss or tinnitus if exposure is prolonged. As the magnetic field surrounds the entire planet, there is no escape from this noise, making it a constant and potentially debilitating issue during a magnetic storm.Secondly, magnetic storms can also have a thermaleffect on the human body. As the magnetic fielddisturbances interact with the Earth's atmosphere, they can cause changes in the distribution of heat, leading to localized increases in temperature. This can result in a feeling of warmth or even mild fever, particularly in those who are already heat-sensitive or have compromised thermoregulatory systems.In addition to these physical effects, magnetic storms can also have a psychological impact on humans. The changes in the magnetic field can affect our cognitive abilities, leading to feelings of confusion, fatigue, and even anxiety. This is particularly true for those who are alreadysensitive to electromagnetic fields or who have a historyof neurological conditions.Moreover, magnetic storms can also interact with electrical systems, including those within our bodies. Our nervous system and cardiovascular system, for example, rely on a delicate balance of electrical signals to function properly. During a magnetic storm, these signals can be disrupted, leading to a range of symptoms includingheadache, nausea, and even arrhythmias.The impact of magnetic storms on human health is complex and multifaceted. From the physical discomfort of ear discomfort and thermal effects to the psychologicaltoll of cognitive impairment and anxiety, these storms can have a significant negative impact on our well-being. While the exact mechanisms of these effects are still being studied, it is clear that magnetic storms have thepotential to significantly disrupt our lives.In conclusion, magnetic storms are a powerful natural phenomenon that can have profound effects on the human body. From ear discomfort and thermal effects to cognitive impairment and psychological distress, these storms can significantly alter our physical and mental states. It is therefore important to be aware of the potential risks andto take appropriate precautions during a magnetic storm, including minimizing exposure to the increased magneticfield noise, maintaining a comfortable body temperature,and seeking medical attention if symptoms persist or worsen.。
五年级英语阅读理解之地球科学探索25题1<背景文章>The Earth is a very interesting planet. It has different layers inside. The outermost layer is called the crust. The crust is what we live on. It is relatively thin compared to the other layers. Beneath the crust is the mantle. The mantle is much thicker and it is made up of hot, semi - liquid rock. It can flow slowly over time. Deeper inside the Earth is the core. The core is divided into two parts, the outer core and the inner core. The outer core is liquid metal, mainly iron and nickel. The inner core is solid, also mostly iron and nickel. These different layers play important roles in many things, such as the Earth's magnetic field and the movement of tectonic plates.1. <问题1>What is the outermost layer of the Earth?A. The mantleB. The crustC. The outer coreD. The inner core答案：B。
Magnetic Field Effects in ChemicalReactions自从法国科学家Louis Pasteur在1860年代首次提出手性分子的概念以来，有机合成、生物化学、医学等领域的研究都受益于对化学反应的深入理解。
而在过去的几十年里，科学家们逐渐开始关注起磁场对化学反应的影响，这被称为磁场效应（Magnetic Field Effects，简称MFE）。
磁场效应的研究对于深入了解生物体系、开发新药物、设计具有新颖应用的分子器件等方面都有着重要意义。
1. 磁场对光化学反应的影响光化学反应是广泛存在于自然界中的一类重要反应。
磁场效应的研究最初正是从光化学反应入手的。
在1950年代初期，英国科学家R.H. Cole曾经报道了磁场对光化学反应的影响，称之为MCE（Magnetic Field Effects in Photochemistry，光化学中的磁场效应）。
随着技术的发展，MCE成为了一种可以测量的现象，并逐渐拓宽到化学反应的其他领域。
2. 磁场对光谱的影响近些年来，各种磁场效应在光谱学领域中被提出。
最早的是磁场调制荧光光谱（Magnetic Field-Modulated Fluorescence Spectroscopy，简称MFMFS），可以应用于荧光标记实验和DNA诊断。
此外，还有磁效应核磁共振（Magnetic Field Effects in NMR，简称MFENMR）和磁效应电子自旋共振（Magnetic Field Effects in ESR，简称MFESR），它们在化学反应研究中的应用也越来越广泛。
3. 磁场对化学反应机理的影响磁场效应并不影响原子、分子、物理和化学反应的基本规律性质。
但是，在某些情况下，磁场可以影响分子或大分子体系中电子或核自旋的相对方向，以至于影响化学反应的机理和产物。
这是由于化学反应发生在两个不对称的状态之间，其能垒是相等的，但由于磁场的作用，使得两个状态的能垒不同。
a r X i v :p h y s i c s /0203040v 2 [p h y s i c s .a t o m -p h ] 24 J u n 2002EPJ manuscript No.(will be inserted by the editor)Magnetic Field Effects on the 1083nm Atomic Line of HeliumOptical Pumping of Helium and Optical Polarisation Measurement in High Magnetic FieldE.Courtade 1,F.Marion 1,P.-J.Nacher 1a ,G.Tastevin 1,K.Kiersnowski 2,and T.Dohnalik 21Laboratoire Kastler Brossel b ,24rue Lhomond,75231Paris cedex 05,France.2Marian Smoluchowski Institute of Physics,Jagiellonian University,ul.Reymonta 4,30-059Krak´o w,Poland.February 2,2008Abstract.The structure of the excited 23S and 23P triplet states of 3He and 4He in an applied magneticfield B is studied using different approximations of the atomic Hamiltonian.All optical transitions (line positions and intensities)of the 1083nm 23S-23P transition are computed as a function of B .The effect of metastability exchange collisions between atoms in the ground state and in the 23S metastable state is studied,and rate equations are derived,for the populations these states in the general case of an isotopic mixture in an arbitrary field B .It is shown that the usual spin-temperature description remains valid.A simple optical pumping model based on these rate equations is used to study the B -dependence of the population couplings which result from the exchange collisions.Simple spectroscopy measurements are performed using a single-frequency laser diode on the 1083nm transition.The accuracy of frequency scans and of measurements of transition intensities is studied.Systematic experimental verifications are made for B =0to 1.5T.Optical pumping effects resulting from hyperfine decoupling in high field are observed to be in good agreement with the predictions of the simple model.Based on adequately chosen absorption measurements at 1083nm,a general optical method to measure the nuclear polarisation of the atoms in the ground state in an arbitrary field is described.It is demonstrated at B ∼0.1T,a field for which the usual optical methods could not operate.PACS.32.60.+i Zeeman and Stark effects –32.70.-n Intensities and shapes of atomic spectral lines –32.80.Bx Level crossing and optical pumping1IntroductionHighly polarised 3He is used for several applications in various domains,for instance to prepare polarised targets for nuclear physics experiments [1],to obtain spin filters for cold neutrons [2,3],or to perform magnetic resonance imaging (MRI)of air spaces in human lungs [4,5].A very efficient and widely used polarisation method relies on op-tical pumping of the 23S metastable state of helium with 1083nm resonant light [6,7].Transfer of nuclear polarisa-tion to atoms in the ground state is ensured by metastabil-ity exchange collisions.Optical Pumping (OP)is usually performed in low magnetic field (up to a few mT),required only to prevent fast relaxation of the optically prepared orientation.OP can provide high nuclear polarisation,up to 80%[8],but efficiently operates only at low pressure (of order 1mbar)[9].Efficient production of large amounts of polarised gas is a key issue for most applications,which often require a dense gas.For instance,polarised gas must2 E.Courtade et al.:The 1083nm Helium Transition in High Magnetic Fieldin the structures of the different excited levels of helium.In order to populate the 23S metastable state and per-form OP,a plasma discharge is sustained in the helium gas.In the various atomic and molecular excited states which are populated in the plasma,hyperfine interaction transfers nuclear orientation to electronic spin and orbital orientations.The electronic angular momentum is in turn converted into circular polarisation of the emitted light or otherwise lost during collisions.This process is actu-ally put to use in the standard optical[8,17]in which the circular polarisation of a spectral line emitted by the plasma is nuclear polarisation is inferred.The an applied magnetic field unfortunately sitivity of the standard optical detection 10mT,and hence a different measurement be used in high fields.This transfer of an adverse effect in OP situations by of nuclear polarisation in the gas.The of an applied field reduces this polarisation thus significantly improve the OP ations of limited efficiency,such as low high pressures.At low temperature (4.2metastability exchange cross section sets a neck and strongly limits the efficiency of OP field increase from 1to 40mT was observed increase in nuclear polarisation from 17%to situation [21].At high gas pressures (above the proportion of metastable atoms is creation of metastable molecular species is factors which tend to reduce the efficiency not surprising that a significant by suppressing relaxation channels in high A systematic investigation of various vant for OP in non-standard conditions (high high pressure)has been made,and results elsewhere [22,23].As mentioned earlier,an surement method of nuclear polarisation in must be developed.It is based on ments of a probe beam,and requires a of magnetic field effects on the 1083nm In this article we report on a detailed study an applied magnetic field on the structure of 23P atomic levels,both in 3He and 4He.In cal section we first present results obtained effective Hamiltonian and discuss the puted line positions and intensities at fields,then discuss the effect of an applied metastability exchange collisions between and the 11S 0ground state level of helium.mental section we present results of line positions and intensities up to 1.5T,optical measurement technique of the nuclear of 3He.Let us finally mention that these principally motivated by OP developments,results could be of interest to design or ments performed on helium atoms in the 23S in an applied field,as long as metrological required.This includes laser cooling and Zeeman slowing [24]of a metastable atom beam,magnetic trapping and evaporative cooling which recently allowed two groups to obtain Bose Einstein condensation with metastable 4He atoms [25,26],and similar experiments which may probe the influence of Fermi statistics with ultracold metastable 3He atoms.E.Courtade et al.:The 1083nm Helium Transition in High Magnetic Field 3analyse the results of fine-structure intervals measured us-ingmicrowave transitions in an applied magnetic field in 4He [33]and 3He [34].All this work has produced a wealth of data which may now be used to compute the level structures and transi-tion probabilities with a very high accuracy up to high magnetic fields (several Tesla),in spite of a small per-sisting disagreement between theory and experiments for the g -factor of the Zeeman effect in the 23P state [32,35].However,such accurate computation can be very time-consuming,especially for 3He in which fine-structure,hy-perfine and Zeeman interaction terms of comparable im-portance have to be considered.A simplified approach was proposed by the Yale group [36],based on the use of an effective Hamiltonian.The hyperfine mixing of the 23P and singlet 21P states is the only one considered in this effective Hamiltonian,and its parameters have been ex-perimentally determined [34].A theoretical calculation of the 3He 23P structure with an accuracy of order 1MHz later confirmed the validity of this phenomenological ap-proach [37].In the present article,we propose a further simplification of the effective Hamiltonian introduced by the Yale group,in which couplings to the singlet states are not explicitly considered.Instead we implicitly take into account these coupling terms,at least in part,by using the 23P splittings measured in zero field to set the eigenvalues of the fine-structure matrices.Results obtained using this simplified effective Hamil-tonian will be compared in section 2.1.3to those of the one including the couplings to the 21P levels,with 3or 6addi-tional magnetic sublevels,depending on the isotope.The effect of additional terms in a more elaborate form of the Zeeman Hamiltonian [32]than the linear approximation which we use will also be evaluated.2.1A simple effective Hamiltonian 2.1.1NotationsThe 11S ground level of helium is a singlet spin state (S =0),with no orbital angular momentum (L =0),and hence has no total electronic angular momentum (J =0).In 3He,the nucleus thus carries the only angular momen-tum I ,giving rise to the two magnetic sublevels m I =±1/2.Their relative populations,(1±M )/2,define the nuclear polarisation M of the ground state.The level structure of 4He excited states is determined from the fine-structure term and the Zeeman term in the Hamiltonian.The fine-structure term H fs is easily ex-pressed in the total angular momentum representation (J )using parameters given in tables 4and 5in the Appendix.For the Zeeman term in the applied magnetic field B we shall use the simple linear form :H (4)Z =µB (g ′L L +g ′S S )·B.(1)The values of Bohr magneton µB ,and of the orbital andspin g -factors g ′Land g ′S are given in table 6in the Ap-pendix.The situation is quite simple for the 23S state,forwhich the 3sublevels |m S (with m S =±1,0)are eigen-states at any field.For the 23P state the Zeeman termcouples sublevels of different J (which however have the same m J )and is more easily expressed in the decoupled (L,S )representation.We note |m L ,m S the vectors of the decoupled basis used in the (L,S )representation and |J ;m J those of the coupled basis,which are the zero-field 9eigenstates of the 23P state.We call Z 1to Z 9(by increas-ing value of the energy,see figure 2)the 9sublevels of the 23P state in arbitrary field.To simplify notations used in the following,we similarly call Y 1to Y 3the 3sublevels of the 23S state.Fig.2.Left :magnetic sublevels of 4He in the 23S (bottom)and 23P (top)levels in very low magnetic field.J is thus a good quantum number and m J is used to differentiate the atomic states.When a small field is applied,the sublevel degeneracies are removed and energies increase for increasing values of m J (i.e.from Z 1to Z 9).Right :magnetic sublevels of 3He in very low magnetic field.F and m F are now good quantum numbers to differentiate the atomic states.Only the F =3/2P x and P y states involve a strong mixing of states of different J values [7].Energies increase for increasing values of m F for all sublevels except in the 23P 0state (i.e.from A 1to A 6and B 1to B 16).The transition probabilities of all components of the 1083nm line are evaluated using the properties of the elec-tric dipole transition operator.For a monochromatic laser light with frequency ω/2π,polarisation vector e λ,and in-tensity I las (expressed in W/m 2),the photon absorption4 E.Courtade et al.:The 1083nm Helium Transition in High Magnetic Fieldrate for a transition from Y i to Z j is given by :1m e ωΓ′I las(Γ′/2)23mc 2f,(3)from which Γ=1.022×107s −1is obtained.Atomic colli-sions contribute to Γ′by a pressure-dependent amount oforder 108s −1/mbar [40].The transition matrix elementsT(4)ij (e λ)are evaluated in the (L,S )representation for each of the three light polarisation states λ=x ±iy (circularly polarised light σ±propagating along the z -axis set by the field B )and λ=z (transverse light with πpolarisation)using the selection rules given in table 7in the Appendix.The transformation operator P 4given in table 10in the Appendix is used to change between the (L,S )and the (J )representations in the 23P state of 4He and thus write a simple 9×9matrix expression for the Hamiltonian in the (L,S )representation,H 9:H 9=P −14H 9fs P 4+H 9Z ,(4)where H 9fs is the diagonal matrix of table 4in the Ap-pendix and H 9Z the diagonal matrix written from equa-tion 1.The level structure of 3He excited states is determined from the total Hamiltonian,including hyperfine interac-tions.The fine-structure term H fs is expressed in the to-tal angular momentum representation (J )using slightly different parameters (table 5in the Appendix)due to the small mass dependence of the fine-structure intervals.For the Zeeman term we also take into account the nuclear contribution:H (3)Z =µB (g ′L L +g ′S S +g I I )·B.(5)The values of all g -factors for 3He are listed in table 6in the Appendix.For the hyperfine term,we consider the simple contact interaction between the nuclear and elec-tronic spins and a correction term H corhfs :H hfs =A L I ·S +H corhfs .(6)The matrix elements of the main contact interaction term in the decoupled (S,I )representation and the values of the constants A S and A P for the 23S and 23P states are given in table 8in the Appendix.The correction term only exists for the 2P state [36,37].When restricted to the triplet levels,it only depends on 2parameters which are given with the matrix elements in table 11in the Appendix.As in the case of 4He,we compute level structure in the decoupled representation,now (L,S,I ).The vectors of the decoupled bases are noted |m S :m I for the 23S state,and |m L ,m S :m I for the 23P state.For the 23S state,the 6×6matrix expression H 6of the Hamiltonian is :H 6=H 6Z +F 6,(7)where H 6Z is the diagonal matrix written from equation 5and F 6the matrix representation of H hfs (table 8in the Appendix).For the 23P state,the 18×18matrix H 18isconstructed from H 9fs ,F 6,H corhfs and H (3)Z :m ′L ,m ′S :m ′I |H 18|m L ,m S :m I =δ(m ′I ,m I ) m ′L ,m ′S |H 9fs |m L ,m S+δ(m ′L ,m L ) m ′S :m ′I |F 6|m S :m I +m ′L ,m ′S :m ′I H corhfs +H (3)Z m L ,m S :m I .The mass-dependent constants in H 9fs and F 6are set tothe values given for 3He in the Appendix.Notations similar to those of the zero-field calculation of reference [7]are used.The 6sublevels of the 23S state are called A 1to A 6,the 18levels of the 23P state B 1to B 18by increasing values of the energy (see figure 2)1.An alternative notation system,given in table 12in the Appendix,is also used for the 6sublevels of the 23S state when an explicit reference to the total angular momentum projection m F is desired.Transition probabilities from A i to B j due to monochromatic light are given by a formula similar to equation 2:1m e ωΓ′I las(Γ′/2)21There is a difference with notations used in reference [7]:within each level of given F,labelling of state names was in-creased for convenience from largest to lower values of m F .In an applied field,this would correspond to an energy decrease inside each of the F levels (except the P 0,F =1/2level).This is the reason for the new labelling convention,which is more convenient in an applied field.E.Courtade et al.:The1083nm Helium Transition in High Magnetic Field5In the following,the dependence of the transition ma-trix elements on the polarisation vector eλwill not be explicitly written.Given the selection rules described in the Appendix,the polarisation vector corresponding to a non-zero transition matrix element can be unambiguously determined.All optical transition energies ω(4)ij and ωij will be referenced to ω57(0),the energy of the C1transition in null magneticfield,which connects levels A5and A6to levels B7to B10.Energy differences will be notedǫ,for instance:ǫ(4)ij/ =ω(4)ij−ω57(0),ǫij/ =ωij−ω57(0).(10) They are determined from computed energy splittings in the23S and23P states of each isotope.The isotope shift contribution is adjusted toobtain the precisely measured C9-D2interval(810.599MHz,[29]).2.1.2Numerical ResultsNumerical computation of level structure and absorption spectra in an appliedfield B is performed in3steps.Matri-ces H9(for4He),H6and H18(for3He)are computedfirst.A standard matrix diagonalisation package(the double-precision versions of the jacobi and eigsrt routines[41])is then used to compute and sort all eigenvalues(energies) and eigenvectors(components of the atomic states in thedecoupled bases).All transition matrix elements T(4)ij andT ij arefinally evaluated,and results are output tofiles for further use or graphic display.Actual computation time is insignificant(e.g.20ms per value of B on a PC using a compiled Fortran program[42]),so that we chose not to use the matrix symmetries to reduce the matrix sizes and the computational load,in contrast with references [36,37].We thus directly obtain all transitions of the1083 nm line:19transitions for4He(6forσ+and forσ−,7 forπlight polarisation),and70transitions for3He(22for σ+and forσ−,26forπlight polarisation).These num-bers are reduced for B=0to18for4He(the Y2→Z7, i.e.|0 →|1;0 πtransition has a null probability)and to 64for3He(the F=1/2→F=5/2transitions,from A5or A6to any of B1to B6are forbidden by selection rules). Due to level degeneracy,the usual D0,D1and D2lines of4He,and C1to C9lines of3He[7]are obtained for B=0 (figure3,and table9in the Appendix).An applied magneticfield removes level degeneracies (Zeeman splittings appear)and modifies the atomic states and hence the optical transition probabilities.Examples of level Zeeman energy shifts are shown infigure4for the23S state and the highest-lying23P levels(originating from the23P0state at lowfield).In the23S state,the two Zeeman splittings are simply proportional to B(28 GHz/T)for4He,as inferred from equation1.For3He, significant deviations from linearity occur for A2,A3and A5above afield of order0.1T,for which Zeeman shifts are significant compared to the hyperfine splitting.Level crossing of A4and A5(and hence interchange of names Fig.3.Top:Components of the1083nm line in4He(left) and3He(right)for B=0.D J is the usual name of the tran-sition to the23P J level.C1to C9refer to the transitions by increasing energy.C0is the additional lowest energy compo-nent corresponding to a forbidden transition in zerofield(see text).Bottom:positions of all the spectral lines resulting from level splittings and isotope shift.The total frequency span from C1to D0is70.442GHz.of the two states)occurs at0.1619T.A high-field decou-pled regime is almost reached for1.5T(figure4,bottom).Analytical expression for state energies and componentson the decoupled{|m S:m I }basis are given in the Ap-pendix(equations A10to A17).In the23P state,the sit-uation is more complex due tofine-structure interactionsand to the larger number of levels.In particular no levelremains unaffected by B in contrast with the situation for Y2.As a result,πtransitions in4He from Y2to Z3or Z9have non-zero Zeeman frequency shifts,which are pro-portional to B2at low and moderatefield although they originate from the linear Zeeman term in the Hamiltonian (equation1).Even the23P0states,for which level mixing is weakest due to the largefine-structure gap,experience significantfield effects(figure4,top and top insert).The splitting between B17and B18(2.468GHz/T at lowfield) is only weakly affected by the nuclear term in equation5 (±16.2MHz/T),and mostly results from level mixing and electronic Zeeman effects.Examples of optical transition intensities and Zeeman frequency shifts are shown infigure5for4He(πlight polarisation).Shifts of transition frequencies are clearly visible on the projection onto the base plane,the usual Zeeman diagram(in which no line crossing occurs).Large changes are also induced by the appliedfield on the transi-tion probabilities.In particular,the forbidden D1transition (Y2→Z7)has a matrix element which linearly increasesat lowfield(T(4)27=3.3×|B|),and approaches1in highfield (curve labelled b infigure5).The two other strong lines6 E.Courtade et al.:The1083nm Helium Transition in High Magnetic FieldFig.4.Level energies E S and E P of the23S and23P states are computed as a function of the appliedfield B.They result from thefine-structure and Zeeman energy contributions for 4He(dashed lines),with the additional hyperfine contributionsfor3He(solid lines).The inserts are close-ups of the low-field regions.In the23P state(top),only the highest lying levels are shown for simplicity.at highfield(2curves labelled a superimposed infigure5) originate from the low-field Y1→Z2and Y3→Z8tran-sitions of D2and D1lines.All other line intensities tend to0at highfield,in a way consistent with the sum rules of equation9.The splittings of the C8and C9lines of3He at mod-eratefield are displayed infigure6.Circularly polarised light,which is used in OP experiments to deposit angular momentum in the gas,is more efficiently absorbed forσ−polarisation when afield is applied.This can tentatively be related to results of our OP experiments:at B=0.1T, the most efficient pumping line is actually found to be C9,σ−.OP results at B=0.6T reported in reference[15] also indicate thatσ−polarisation is more efficient,in spite offluorescence measurements suggesting an imperfect po-larisation of the light.One must however note that OP efficiency does not only depend on light absorption,and that level structures and metastability exchange collisions (which will be discussed below)also play a key role.Let us finally mention that the forbidden C0transition becomes Fig.5.3D plot of the transition matrix elements forπlight polarisation in4He,T(4)ij(π),(vertical axis)and of transition energy differenceǫ(with respect to C1)as a function of B.To highlight the changes of the transition intensities,the symbolsizes(symbol areas)are proportional to T(4)ij.a and b are the strongest lines in highfield(see text).The projection onto the base plane is the usual Zeeman diagram.allowed in an appliedfield,but that the transition prob-abilities remain very weak and vanish again at highfield.Fig.6.Plot of the Zeeman line shifts for the C8and C9lines of3He.The symbol types refer to different light polarisation states.The symbol sizes(areas)are proportional to the corre-sponding transition matrix elements T ij.E.Courtade et al.:The1083nm Helium Transition in High Magnetic Field72.1.3DiscussionTo assess the consequences of the main approximation inour calculations,namely the restriction of the Hamilto-nian to the triplet23P configuration,we have made a sys-tematic comparison to the results of the full calculationincluding singlet-triplet mixing.In the case of4He,exact energies are of course obtainedfor B=0,and level energy differences do not exceed1kHzfor B=2T.This very good agreement results from thefact that the lowest order contribution of the singlet ad-mixture in the23Pstate to the Zeeman effect is a thirdorder perturbation[30,43].For similar reasons,computedtransition probabilities are also almost identical,and oursimple calculation is perfectly adequate for most purposesif the proper parameters of table5in the Appendix areused.For3He we have compared the results of the full cal-culation involving all24sublevels in the2P states as de-scribed by the Yale group[36]and two forms of the sim-plified calculation restricted to the18sublevels of the23Pstate.The simpler form only contains the contact interac-tion term A P I·S in the hyperfine Hamiltonian of equa-tion6.The more complete calculations makes use of thefull hyperfine interaction,with the correction term H corhfsintroducing two additional parameters,d and e.The simpler1-parameter calculation is similar to thezero-field calculation of reference[7](with updated valuesof all energy parameters),and provides a limited accuracyas shown infigure7.Errors on the computed energies ofFig.7.Errors in calculated energies for the18sublevels of the3He23P state resulting from the sole use of the contact termA P I·S in the hyperfine Hamiltonian are plotted for differentmagneticfield rge changes of the errors occurclose to level anticrossings(e.g.m F=1/2B15and B17levelsclose to1.18T,seefigure4).the levels of several tens of MHz cannot be significantly re-duced by adjusting A P to a more appropriate value.Thisis a direct evidence that the correction term H corhfsunam-biguously modifies the energy level diagram,with clearfield-dependent signatures at moderatefield and around1T.Errors on the transition matrix elements up to a few10−3also result from neclecting H corhfs.Using this simple1-parameter form of the hyperfine Hamiltonian should thusbe avoided when a better accuracy is desired.The3-parameter calculation has also been comparedto the full calculation,and a slight adjustment of param-eters A P,d and e with respect to the corresponding pa-rameters C,D/2and E/5of the full calculation(whichalso includes the off-diagonal parameter C′[36]),now pro-vides a more satisfactory agreement for the level energies,shown infigure8.Transitions matrix elements T ij are alsoFig.8.Errors in calculated energies for the18sublevels of the3He23P state resulting from the use of the full3-parameterhyperfine Hamiltonian are plotted for different magneticfieldintensities.As infigure7,large changes of the errors occurclose to the B15-B17level anticrossing around1.18T.obtained with good accuracy(1.3×10−4r.m.s.differenceon average for all transitions andfields,with a maximumdifference of5×10−4).The values of the3parameters A P,d ande differ by-0.019%,3.4%and4.6%from the corre-sponding parameters in the full calculation.This adjust-ment may effectively represent part of the off-diagonal ef-fects in the singlet admixture,and allows to decrease theenergy errors,especially below1T(by a factor2-3).The other important approximation in our calculationsis related to the simplifications in the Zeeman Hamiltonianwritten in equations1and5.Thefirst neglected term isthe non-diagonal contribution proportional to the smallparameter g x in equation A1.The non-zero elements ofthis additional contribution are of orderµB Bg x/5,i.e.1-2MHz/T in frequency units.The other neglected termresults from the quadratic Zeeman effect[30,32,43],whichintroduces matrix elements of order(µB B)2/R∞(R∞=3.29×106GHz stands for the Rydberg constant in fre-quency units),i.e.60kHz/T2.For most applications,andin particular for the experimental situations considered inthe following,corrections introduced by these additional8 E.Courtade et al.:The1083nm Helium Transition in High Magnetic Field terms in the Zeeman Hamiltonian would indeed be negli-gible,not larger for instance than the errors infigure8.2.2Metastability exchangeSo far we have only addressed the effects of an appliedmagneticfield on the level energies and structures of the23S and23P states of helium,and the consequences for the1083nm optical transition.In this section we now considerthe effect of the appliedfield on the angular momentumtransfer between atoms during the so-called metastabilityexchange(ME)collisions,which are spin-exchange binarycollisions between an atom in the ground state and onein the metastable23S state.They play an important rolein all experimental situations where the atoms in the23Sstate are a minority species in a plasma(e.g.with a num-ber density1010–1011cm−3compared to2.6×1016for thetotal density of atoms at1mbar in typical OP conditions).These collisions may be neglected only for experiments onatomic beams or trapped atoms for which radiative forcesare used to separate the metastable atoms from the muchdenser gas of atoms in the ground state.To describe the statistical properties of a mixture ofground state and23S state atoms we shall use a standarddensity operator formalism and extend the treatment in-troduced by Partridge and Series[44]for ME collisions,later improved[45,46]and used for an OP model[7],tothe case of an arbitrary magneticfield.Ourfirst goal isto show that the“spin temperature”concept[47,48,7]re-mains valid,and that the population distribution in the23S state is fully determined(in the absence of OP and ofrelaxation)by the nuclear polarisation M of the groundstate.This is the result on which the optical detectionmethod of section3.3relies.The second goal is to providea formalism allowing to study the consequences of hyper-fine decoupling on spin transfer during ME collisions.2.2.1Derivation of rate equationsWe shall consider situations in which no resonance is drivenbetween the two magnetic sublevels of the ground state of3He(the ground state of4He has no structure)nor be-tween sublevels of the23S state.We can thus a prioriassume that the density operatorsρg(in the ground stateof3He),ρ3(in the23S state of3He)andρ4(in the23Sstate of4He)are statistical mixtures of eigenstates of theHamiltonian.The corresponding density matrices are thusdiagonal and contain only populations(no coherences).With obvious notations:ρg=1+M2|− −|(11)ρ3= 61a i|A i A i|(12)ρ4= 31y i|Y i Y i|,(13) where a i and y i are relative populations( a i= y i=1).An important feature of ME in helium is that in prac-tice no depolarisation occurs during the collisions,due to the fact that all involved angular momenta are spins[46]. Three kinds of ME collisions occur in an isotopic mixture, depending on the nature of the colliding atoms(3He or 4He)and on their state(ground state:3,4He,23S state: 3,4He∗).1.Following a ME collision between3He atoms:3He+3He∗→3He∗+3Heρgρ3ρ′3ρ′gthe nuclear and electronic angular momenta are re-combined in such a way that the density operators just after collisionρ′g andρ′3are given by:ρ′g=Tr eρ3(14)ρ′3=ρg⊗Tr nρ3(15) where Tr e,Tr n are trace operators over the electronic and nuclear variables respectively[45].2.Following the collision between a ground state4Heatom and a23S state3He atom:4He+3He∗→4He∗+3Heρ3ρ′′4ρ′′gthe density operators just after collision are:ρ′′g=Tr eρ3(16)ρ′′4=Tr nρ3.(17) 3.Following the collision between a23S state4He atomand a ground state3He atom:3He+4He∗→3He∗+4Heρgρ4ρ′′′3the density operator of the outgoing23S state3He atom is:ρ′′′3=ρg⊗ρ4.(18) The partial trace operations in equations14to17 do not introduce any coherence term in density matri-ces.In contrast,the tensor products in equations15and 18introduce several off-diagonal terms.These are driving terms which may lead to the development of coherences in the density operators,but we shall show in the fol-lowing that they can usually be neglected.Since m F is a good quantum number,off-diagonal terms in the ten-sor products only appear between2states of equal m F. With the state names defined in the Appendix(table12), these off-diagonal terms are proportional to the operators A h+ A l+ and A l+ A h+ (for m F=1/2), A h− A l− and A l− A h− (for m F=-1/2).These four operators contain a similar sinθ±cosθ±factor,whereθ+andθ−arefield-dependent level mixing parameters(see equations A14to A17in the Appendix).They have a time evolution char-acterised by a fast precessing phase,exp(i∆E±t/ ),de-pending on the frequency splittings∆E±/ of the eigen-states of equal m F.。
