基于光偏振旋转效应的碱金属气室原子极化率测量方法及影响因素分析

利用原子自旋效应能够实现超高灵敏度的惯性和磁场测量。一类操控原子自旋处于无自旋交换弛豫态的器件可以进行物理参数测量。碱金属气室为该类器件的敏感表头。碱金属原子密度与原子极化率是碱金属气室的重要参数,对研究原子自旋处于无自旋交换弛豫态有着重要的作用。光的偏振效应在量子计算和原子物理研究中发挥了重要作用。利用光的偏振效应能够实现对碱金属原子密度与原子极化率的检测。提出一种基于光偏振旋转效应的碱金属原子极化率测量方法。首先对碱金属气室加恒定磁场,利用激光作为检测光,根据光偏振旋转原理,检测通过气室的偏振光的法拉第旋转角,得到碱金属气室原子密度。然后将碱金属原子抽运,利用激光作为检测光,检测通过气室的偏振光的偏转角,得到碱金属原子极化率。该方法在测量原子极化率的过程中也测量了碱金属原子密度,实现利用一套系统测量两个重要参数,具有快速测量和高灵敏度等特点,简化了实验设备及过程。对两种偏转角进行仿真分析,得到该方法实验时检测激光波长变化对偏转角的影响,根据仿真图得到检测激光波长的可取范围,验证了该方法的可行性。最后分析激光器波长波动与磁场波动对其测量精度的影响,提出实验对激光器与磁场的要求。     

A modified analytical model of the alkali-metal atomic magnetometer employing longitudinal carrier field

Alkali-metal atomic magnetometers employing longitudinal carrier magnetic field have ultrahigh sensitivity to measure transverse magnetic fields and have been applied in a variety of precise-measurement science and technologies. In practice, the magnetometer response is not rigorously proportional to the measured transverse magnetic fields and the existing fundamental analytical model of this magnetometer is effective only when the amplitudes of the measured fields are very small. In this paper, we present a modified analytical model to characterize the practical performance of the magnetometer more definitely. We find out how the longitudinal magnetization of the alkali metal atoms vary with larger transverse fields. The linear-response capacity of the magnetometer is determined by these factors: the amplitude and frequency of the longitudinal carrier field, longitudinal and transverse spin relaxation time of the alkali spins and rotation frequency of the transverse fields. We give a detailed and rigorous theoretical derivation by using the perturbation-iteration method and simulation experiments are conducted to verify the validity and correctness of the proposed modified model. This model can be helpful for measuring larger fields more accurately and configuring a desirable magnetometer with proper linear range.     

On the effect of photoinduced emission of alkali atoms from a paraffin coating on the rate of spin relaxation of atoms in the volume of a cell

The effect of photoinduced emission of alkali atoms from the paraffin coating of a cell on the spin relaxation time of the atoms was studied experimentally. No effect was detected. It was additionally found that long irradiation of the cell surface by light with a power density of about 1 mW/cm² does not cause any degradation of the coating in spite of almost complete removal of the atoms from the coating due to their photostimulated diffusion in the layer and photodesorption. After the irradiation is complete, the surface contacting with the alkali vapor is again saturated with the alkali atoms with a time constant of about 1 h.     

Impedance-type measurements using XPS

An impedance type of measurement using X-ray photoelectron spectroscopy is applied for probing charging/discharging dynamics of a sample containing Rb deposited on a SiO₂/Si substrate containing an octadecyltrichlorosilane (OTS) bilayer coating. The OTS bilayer coatings have possible use as anti-relaxation wall coatings for alkali atom vapor cells in miniaturized instruments such as chip-scale atomic clocks, and/or magnetometers. The measurement consists of the application of bipolar square wave pulses of ±10.0 V amplitude to the sample with varying frequencies in the range of 10⁻² to 10² Hz while recording X-ray photoemission data. For a conducting sample this type of measurement twins all the photoemission peaks at −10.0 and +10.0 eV positions at all frequencies with exactly 20.0 eV difference between them. However, for samples amenable to charging, the difference between the twinned peaks is less than 20.0 eV, and gradually decreases at correspondingly lower frequencies. For the sample under consideration here at 0.01 Hz, the twinned O1s and Si2p peaks, representing the SiO₂ substrate, are separated by 18.2 eV, displaying a 1.8 eV charging shift. These positions differ from those of the C1s (18.0 eV) representing the OTS bilayer and the Rb3d peaks (18.1 eV). These results reveal that the Rb is electrically (perhaps also chemically) isolated from the OTS bilayer, which may be correlated with the improved performance of the OTS bilayers as anti-relaxation coatings in these alkali atom magnetometer cells.     

Concept of an Optical Magnetometer Based on the Spectroscopy of Alkali Vapors Confined in Nanometric-Thick Cells

In this article, we present the concept of an optical scalar magnetometer based on the spectroscopy of hot alkali vapors confined in nanometric-thick cells. We present an appropriate theoretical model to describe the interaction of linearly and circularly polarized light with atomic alkali vapors confined in extremely thin cells where a longitudinal magnetic field is applied. This model can be used to perform consecutive fittings of experimental spectra recorded by derivative selective reflection method, in order to measure the value of magnetic field. We illustrate the model with various calculated spectra for natural Rb vapor, while equivalent results hold for other alkalis (Na, K, Cs). We analyze the feasibility of the concept for different cases depending on light polarization and cell thickness, and discuss possible limitations of the technique.     

Depolarization of the photoluminescence and spin relaxation in n-doped GaAs

Optically oriented electron spin lifetime in n-doped gallium arsenide was measured via depolarization of the photoluminescence (PL) in a transverse magnetic field (Hanle effect). In order to measure the PL polarization, a time-resolved pump-probe experiment, where a pump pulse generates spin-polarized electrons and a probe pulse monitors their polarization, was employed. The PL polarization in dependences of the pump-probe delay, external magnetic field as well as of the sample temperature was studied. The PL polarization was found to decay exponentially with the pump-probe delay, from which the spin lifetime of the electrons was measured. The measured value was found to depend on the strength of the magnetic field and sample temperature.     

延长Rb原子退相干时间镀膜材料的可行性研究

实验测量了镀石蜡Rb池和石英玻璃Rb池中Rb原子自旋态寿命.研究表明,镀石蜡Rb池的Rb原子自旋态寿命在温度T=50℃约为7ms,而在同样温度的石英玻璃池中,Rb原子自旋态寿命仅为20μs.这为基于自旋的量子存储实验提供了很好的借鉴.同时讨论了其他候选的材料来隔绝碱金属原子和容器壁的非弹性碰撞相互作用.根据实验结果,我们认为H原子布于笼状结构内部的C60H60以及BN材料有较大的实用前景.     

抽运-检测型非线性磁光旋转铷原子磁力仪的研究

报道了一种抽运-检测型的非线性磁光旋转铷原子磁力仪.其原理是线偏振光通过处于外磁场环境中被极化的原子介质后,由于原子对线偏振光中左、右圆偏成分不同的吸收和色散,导致光的偏振方向会产生与磁场相关的转动.分析了该磁力仪的工作原理,并测试了它对不同磁场大小的响应.测试结果表明,磁力仪测量范围为100—100000 nT,极限灵敏度为0.2 p T/Hz~(1/2),磁场分辨率为0.1 p T.进一步研究了不同磁场下原子系综极化态的横向弛豫时间,讨论了原子磁力仪高磁场采样率的获得方法.本文的原子磁力仪在5000—100000 n T的磁场测量范围内磁场采样率可实现1—1000 Hz范围内可调,能够测量低频的微弱交变磁场.本文的研究内容为大磁场测量范围、高灵敏度、高磁场采样率的原子磁力仪研制提供了重要参考.     

碱金属气室无磁电加热技术研究与系统设计

基于量子精密测量的原子自旋陀螺仪具有高精度、小体积、低成本等优势,被认为是未来陀螺仪的发展方向;原子自旋陀螺仪的核心部件是承载原子自旋的碱金属气室;碱金属气室加热温度的稳定性是决定原子自旋陀螺仪精度和灵敏度的重要因素之一;同时,原子自旋陀螺仪的高灵敏度使其对磁场噪声极其敏感,因此要求加热过程不能引入额外的磁场干扰;针对以上要求,对原子自旋陀螺仪的无磁电加热技术进行了研究;设计并搭建了以Pt1000作为温度传感器,双层对称结构的加热膜作为加热元件,结合源测量单元、数据采集板卡、正弦波信号发生电路、驱动电路以及LabVIEW软件平台构成的无磁电加热系统;通过实验测试,本系统引入的等效干扰磁场优于15 fT/Hz1/2,气室温度短期稳定度优于±5 mK,长期稳定度优于±10 mK,为原子自旋陀螺仪的性能提升提供了可靠保障。     

Spin and electric field gradient texture studies by Mössbauer spectroscopy with polarized gamma rays

From Mössbauer spectra of⁵⁷Fe with elliptically polarized radiation we fit the coefficients of the spin (or electric field gradient) texture function expanded in real spherical harmonics up to 1=2. We determine, and show in perspective graphs, the spin texture of the surface of a transformer metal sheet (Fe?Si), of magnetic videotapes (demagnetized and magnetized) and the electric field gradient texture of a powder of an organometallic compound. We calculate some averages that have an important physical significance.     

Spin polarization in a freely evolving sample of cold atoms

We have implemented and optimized a technique of spin polarization by optical pumping in a caesium atomic fountain, gaining a nearly fivefold increase in the useful cold atom signal in detection. This allows an improvement of the fountain clock stability without compromising its accuracy. We present a detailed study of optical pumping in a freely evolving cloud of cold caesium atoms: we have investigated theoretically and experimentally the dynamics of the pumping process and the associated heating due to random photon scattering. The heating limits the potential gain in the fountain signal due to an additional cloud expansion. A high degree of spin polarization was achieved with accumulation of up to 97 % of the population in a single magnetic (m _F  = 0) sublevel of the ground state. Factors affecting the achievable spin polarizations, such as the purity of the pumping light polarization and the shadowing effect in the cloud, were considered. This technique may also be used in atom interferometers and for other alkali metal systems.     

Influence of in-plane magnetic field on spin polarization in the presence of the oft-neglected k-Dresselhaus spin-orbit coupling

The influence of in-plane magnetic field on spin polarization in the presence of the oft-neglected k³-Dresselhaus spin-orbit coupling was investigated. The k³-Dresselhaus term can produce a limited spin polarization. The in-plane magnetic field plays a great role in the tunneling process. It can generate the perfect spin polarization of the electrons and the ideal transmission coefficient for spin up and down simultaneously. In energy scale, complete separation between spin up and down resonance was obtained by a relatively higher in-plane magnetic field while a comparatively lower in-plane magnetic field vanishes the spin separation. On the other hand, the spin relaxation can be suppressed by compensating the oft-neglected k³-Dresselhaus spin orbit coupling using a relatively lower in-plane magnetic field.     

极化检测型铷原子磁力仪的研究

针对交变弱磁场的检测,研制了一种基于极化-检测双光束结构的激光抽运铷原子磁力仪.为了获得该磁力仪对磁场的响应特性,通过数值仿真分析了信号幅度随极化磁场强度、弛豫时间的变化关系,并进行了实验验证.最后通过选择合适的极化磁场使磁力仪对待测磁场的灵敏度最大.实验结果表明,优化后磁力仪灵敏度为0.2pT/(Hz)~(1/2),响应带宽3.5kHz,可用于弱磁场磁共振、高频异常物理现象等信号的检测.     

冷原子系综中两正交光场偏振模高效率存储的实验研究

高效率光量子信息存储是可扩展光量子信息处理的一个重要工具.本文对一个冷原子系综中两正交光场偏振模的高效率存储进行了实验研究.通过在雪茄型冷原子系统上施加一个中等强度的磁场,消除了原子Zeeman子能级的简并性,从而使磁敏感自旋波从电磁感应透明系统中被移出,由此完成了两正交光场偏振模高效率、长寿命的量子存储.实验测量了两偏振模存储效率与存储时间以及实验重复频率的关系,结果表明,随着重复频率的增加,存储效率逐渐降低,在10 Hz时,测量得到两偏振模存储效率为30%,同时存储寿命达到3 ms.测量结果为偏振纠缠在冷原子系统中的存储提供了重要的实验基础.     

Can spinor dipolar effects be observed in Bose-Einstein condensates?

Weak dipolar effects in atomic Bose-Einstein condensates (BECs) have recently been predicted to develop spin textures. However, observation of the spin textures requires us to decrease the magnetic field down to approximately 10 microG for spin-1 alkali BECs, so that they are not washed out by the Zeeman effect. We present a scheme to observe the magnetic dipole-dipole interaction in alkali BECs under a realistic magnetic field of approximately 100 mG. Our scheme enables us to extract genuine dipolar effects and should apply also to (52)Cr BECs.     

Optically detected electron spin polarization and Hanle effect in AlGaAs/GaAs heterostructures

The spin polarization of optically created conduction electrons in p-type AlGaAs/GaAs heterostructures was observed via the degree of circular polarization of the photoluminescence. Application of a magnetic field perpendicular to the propagation of the light allows one to determine the spin relaxation time T₁ and the electron lifetime τ in the conduction band. By tilting the magnetic field with respect to an estimate of the effective nuclear field acting on the electrons can be obtained.     

Features of the Magnetic Resonance of an Alkali Metal upon Biharmonic Pumping

The dynamics of spin projections of the electron shell of an alkali metal on the coordinate axis is considered in the electron paramagnetic resonance scheme with continuous pumping by biharmonic circularly polarized laser radiation. The working region is a cell with alkali vapor metal vapors and a buffer gas at a high concentration at temperature 60°C. It was found that the use of biharmonic pumping causes not only the expected electron-spin precession, but also pulsations of the electron-spin projection on the axis along which the magnetic field is directed. The frequency of these pulsations depends on the nuclear angular momentum of alkali metal atoms. In the case of the transverse electron magnetic resonance, this effect is absent.     

Measurement of electron spin lifetime and optical orientation efficiency in germanium using electrical detection of radio frequency modulated spin polarization

We propose and demonstrate a technique for electrical detection of polarized spins in semiconductors in zero applied magnetic fields. Spin polarization is generated by optical injection using circularly polarized light which is modulated rapidly using an electro-optic cell. The modulated spin polarization generates a weak time-varying magnetic field which is detected by a sensitive radio-frequency coil. Using a calibrated pickup coil and amplification electronics, clear signals were obtained for bulk GaAs and Ge samples from which an optical spin orientation efficiency of 4.8% could be determined for Ge at 1342 nm excitation wavelength. In the presence of a small external magnetic field, the signal decayed according to the Hanle effect, from which a spin lifetime of 4.6±1.0 ns for electrons in bulk Ge at 127 K was extracted.     

Dipole-dipole spin anisotropy energy for spin density waves in highly anisotropic crystals: (TMTSF) 2X

The dipole-dipole spin anisotropy energy for a spin density wave (SDW) is compatible with experimental easy, intermediate, and hard spin polarization axes in the (TMTSF) ₂X class of organic conductors only when electron-hole correlations of the SDW are atomic in size. Magnitudes of the spin anisotropy energy and the spin-flip magnetic field in this case agree with experiment for a SDW amplitude comparable to 10^-2 Bohr magnetons/TMTSF molecule.     

A wide angle neutron spin filter system using polarized He

Polarized ³He neutron spin filters can operate over a wide neutron energy range and provide a large angular acceptance. A compact ³He neutron spin filter system has been developed for the Multi-Axis Crystal Spectrometer at the National Institute of Standards and Technology (NIST) Center for Neutron Research. Sealed ³He cells, polarized by spin-exchange optical pumping, are used as polarizer and analyzer. The polarization of the neutrons incident on the sample is inverted by flipping the polarization of the ³He gas in the polarizer, with only a small effect on the analyzer cells. The cell fabrication process, ³He spin flipper, and the holding magnetic field are discussed and we present the results of a first on-linetest.