铷原子气体自旋噪声谱的测量与改进

利用自主设计并制作的基于现场可编程门阵列的实时傅里叶变换采集卡(FFTsDAC),采用线偏振光检测碱金属铷原子气样品中的自旋随机涨落(即自旋噪声谱).详细讨论了背景噪声以及自旋噪声随探测光光强的变化关系,证实了自旋噪声来自于系统中自旋的随机涨落.对比了两种FFTsDAC(8 bit采样的FFTsDACl和12 bit采样的FFTsDAC2)的测量性能,分析了影响实验信噪比的因素.FFTsDAC2具有更高的测量效率和采样深度以及更长的单次采样时间,因而具有更高的信噪比和更好的频率分辨率,与数值模拟的结果一致.     

Spin Noise Spectroscopy in N-GaAs:Spin Relaxation of Localized Electrons

Spin noise spectroscopy(SNS) of electrons in n-doped bulk GaAs is studied as functions of temperature and the probe-laser energy. Experimental results show that the SNS signal comes from localized electrons in the donor band. The spin relaxation time of electrons, which is retrieved from the SNS measurement, depends on the probe light energy and temperature, and it can be ascribed to the variation of electron localization degree.     

Add/drop filter using in-plane slanted gratings in azo polymers

We have fabricated in-plane slanted gratings on azo-functionalized polymeric films using a fast, direct-writing method. By properly adjusting the resonance, these gratings can be used as 90 degrees integrated reflectors and add/drop filters in the plane of the film. We have produced an attenuation of 14.8 dB at 1560.2 nm with a FWHM of 6.47 nm. Also, a signal of 1548 nm wavelength was added to the output from a different direction. Any light shifted from the resonance will pass through the filter undisturbed.     

扫描相机标定脉冲信号位置的确定及噪声处理

 扫描相机标定数据处理中的一个关键问题是如何准确确定脉冲信号的位置，实验数据的信噪比和脉冲信号位置的定义方法都会对标定结果的准确性产生影响。采用了取半高宽的方法来确定扫描相机标定脉冲信号的位置，在信噪比比较高 （大于100） 的情况下，该方法确定标定信号的位置可以达到亚像素水平。对于信噪比比较低 (小于10) 的实验数据，先采用快速傅里叶变换方法对其进行滤波，通过滤波可以极大地抑制噪声信号的影响，然后采用“半高宽法”确定脉冲信号的位置，最后得出可信的标定结果。当扫描相机定在0.3 ns的扫描档时，通过该方法得到的扫描速度为0.214 ps/pixel,扫描不确定度为0.002 9 ps/pixel,拟合线性相关系数为0.999 7。     

组合刻蚀法制备窄带滤光片列阵

介绍了组合刻蚀法制备窄带滤光片列阵的基本原理和制备工艺,这是一种效率非常高的制备方法,只需N次刻蚀就可以完成2N通道窄带滤光片列阵的制备,而且可以用于制备不同波段窄带滤光片列阵。展示了可见-近红外波段32通道窄带滤光片列阵和中红外波段16通道窄带滤光片列阵的实验结果,其中32通道窄带滤光片列阵的带通峰位基本呈线性分布在774.7~814.2 nm之间,所有滤光片的半峰全宽都非常窄(δλ<1.5 nm),相应于δλ/λ<0.2%,半峰全宽最窄的滤光片达到0.8 nm,相应于δλ/λ<0.1%,其带通峰位λ=794.3 nm;各通道的带通透过率在21.2%~32.4%之间,大部分在30%左右。     

Spin-polarized tunneling spectroscopy of co(0001) surface States

Spin-polarized tunneling was studied on Co surfaces of exchange coupled Co/Cu/Co samples, using an Fe tip. A spin-polarized surface state of Co(0001) was found to exist at -0.43 eV relative to E(F), with FWHM of 0.23 eV in the spectra. The state exhibits negative magnetoresistance with an effective spin polarization of less than -23%, suggesting negatively high spin polarization of the surface state. Our first-principles calculations have supported the existence of the surface state. From the calculation, the state is identified as a minority spin Gamma-centered d(2)(z)-like surface state.     

Resolution Improvement in Optical Coherence Tomography with Segmented Spectrum Management

We demonstrate resolution improvement in an optical coherence tomography (OCT) system with multiple scans of segmented spectral bands and software signal processing. With an effective spectral full-width at half-maximum (FWHM) of 45 nm, centered at 950 nm, we compress the interference fringe FWHM from 31 μm down to 7 μm, which is smaller than the theoretical limit of 8.9 μm if a Gaussian spectral shape is assumed, through the combined effect of dispersion compensation and spectral shaping. With the amplitude adjustments of the OCT images of the segmented spectral bands, side-lobes can be significantly suppressed with a slight increase of the fringe envelope FWHM. With other amplitude adjustments, the envelope FWHM can be reduced to 5.6 μm at the expense of significant side-lobes.     

Sensitivity enhancement in structural measurements by solid state NMR through pulsed spin locking

Free induction decay (FID) signals in solid state NMR measurements performed with magic angle spinning can often be extended in time by factors on the order of 10 by a simple pulsed spin locking technique. The sensitivity of a structural measurement in which the structural information is contained in the dependence of the integrated FID amplitude on a preceding evolution period can therefore be enhanced substantially by pulsed spin locking in the signal detection period. We demonstrate sensitivity enhancements in a variety of solid state NMR techniques that are applicable to selectively isotopically labeled samples, including 13C-15N rotational echo double resonance (REDOR), 13C-13C dipolar recoupling measurements using the constant-time finite-pulse radio-frequency-driven recoupling (fpRFDR-CT) and constant-time double-quantum-filtered dipolar recoupling (CTDQFD) techniques, and torsion angle measurements using the double quantum chemical shift anisotropy (DQCSA) technique. Further, we demonstrate that the structural information in the solid state NMR data is not distorted by pulsed spin locking in the detection period.     

复色光伏孤子的稳定性

给出求解复色孤子半高宽的近似方法，该方法对分析复色光束的演化提供一个定性的基础 .进一步的数值模拟结果表明，当入射双曲正割光束满足复色光伏孤子半高宽与中心光强的 关系时，双曲正割光束在晶体中的传播就非常接近孤子，表明复色光伏孤子对于小的微扰是 稳定的.此外，复色光伏孤子对于小的轴偏离具有较好的稳定性；复色光伏孤子对因温度微 扰引起折射率变化的情况也具有较好的稳定性.一般情况下，初始光强分布接近复色光伏孤 子光强分布的两束光的光强在传播过程中不断地起伏，形成呼吸状结构，但如果入射面处的 光强明显偏离孤子的光 关键词： 复色光伏空间孤子 稳定性     

光注入下外光反馈半导体激光器输出自相关特性研究

基于半导体激光器(SL)受到外部扰动(光反馈和光注入)下的速率方程组,研究了反馈系数、延迟时间、注入强度和频率失谐对半导体激光器输出混沌信号自相关特性的影响.研究表明：上述四个参量对SL输出混沌信号的自相关函数曲线的半高全宽(FWHM)以及边峰抑制比都有影响;通过合理选择各参量,可以使SL输出的混沌信号具有尖锐的自相关函数曲线分布,其FWHM可降到0.02 ns,比已有相关报道提高了一个数量级. 关键词： 半导体激光器 光反馈 光注入 自相关函数     

Integrated optical filter arrays fabricated by using the combinatorial etching technique

A combinatorial etching technique is developed to fabricate integrated narrow bandpass filters on a single substrate. It is highly efficient for fabrication of integrated filter arrays in optical regions. A monolithic filter array has been fabricated by using the technique with a two-step deposition process. The filter contains 32 elements in the near-infrared region. The relative full width at half-maximum (FWHM) sigmalambda/lambda of the filter elements is less than 0.2%. Such a narrow bandpass filter array can be utilized in many optical applications.     

Mapping of the cerebral response to hypoxia measured using graded asymmetric spin echo EPI

Graded asymmetric spin echo-echo planar imaging (ASE-EPI) was used to measure transient alterations in cerebral oxygenation resulting from 60 seconds of anoxia in alpha-chloralose anaesthetised rats. The anoxic period induced a transient fall ( approximately 1 min) in signal intensity followed by a prolonged signal overshoot consistent with an autoregulatory response to oxygen deprivation. The magnitude of signal response, integrated over the entire brain, increased linearly with the echo asymmetry (t(ge)). However, that increase in sensitivity was offset by a reduced signal to noise ratio and quality of the image data. The responses of four regions of interest within the brain to the anoxic stimulus, and the effect of increasing the echo asymmetry, were compared. A comparable magnitude of signal decrease was observed in all brain regions except the superficial cortex that included pial vessels. As t(ge) was incremented differences in signal attenuation between regions became more pronounced. The signal overshoot observed upon restoration of normal breathing gases showed similar trends, producing similar normalised vascular responses for all regions of interest studied. Different regions of interest showed comparable time courses of the signal overshoot suggesting that similar autoregulatory vascular mechanisms operate in all brain regions. These findings additionally show that the use of graded ASE-EPI produced a characteristic profile of maximum signal change measured during and following the anoxic period for each brain region. They suggest that the shape of this profile was determined by the local vasculature within each region of interest; this feature could be exploited in activation studies to eliminate regions with significant signal changes originating from large draining vessels. Finally, the consistent physiological response observed, when the overshoot was compared to the magnitude of the signal drop, demonstrated that modification of the spin echo offset parameter did not mask or detrimentally alter the signal change resulting from the underlying physiological perturbation.     

1.55-μm Si-based MOEMS optical tunable filter

A prototype 1.55-μm Si-based micro-opto-electro-mechanical-systems (MOEMS) tunable filter is fabricated, employing surface micromachining technology. Full-width-at-half-maximum (FWHM) of the transmission spectrum is 23 nm. The tuning range is 30 nm under 50-V applied voltage. The device can be readily integrated with resonant cavity enhanced (RCE) detector and vertical cavity surface emitting laser (VCSEL) to fabricate tunable active devices.     

AlGaAs短波长超辐射集成光源

设计了一种新型半导体集成光源－－ＡｌＧａＡｓ短波长超辐射集成光源。器件为单量子阱、增益导引的氧化物条形结构，采用直接耦合方式将超辐射发光与光放器集成在一起，在脉冲条件下获得了输出功率为５７ｍＷ的超辐射，谱线宽度ＦＷＨＭ为２０ｎｍ，放大器的增益为２１ｄＢ。     

Development of highly integrated RSFQ circuits on the basis of intrinsically shunted Josephson junctions

At PTB, for application in rapid single flux quantum (RSFQ) and voltage standard circuits, the development of highly integrated SDE circuits is focused on devices based on intrinsically shunted Josephson junctions in the SINIS and SNS technologies. In SINIS technology, the fabrication process has been optimized to values of the critical current density of j_C=500 A/cm² and the characteristic voltage of V_C=190 μV. To raise the circuit integration level, successive steps of development are shown by the example of the layout of an elementary RSFQ cell designed for higher values of j_C. In SNS technology, a fabrication process has been developed to produce small ramp-type junctions with contact areas smaller than 0.4 μm² and with values for j_C and V_C of about j_C=200 kA/cm² and V_C=20 μV. The design allows the SNS junction size to be further reduced down to the deep sub-micron range.     

Three-Pulse ELDOR Theory Revisited

The current theory of three-pulse electron double resonance (PELDOR) has been generalized to the case, when paramagnetic particles (spin labels) in pairs or groups have the electron paramagnetic resonance (EPR) spectra, which overlap essentially or coincide. The PELDOR signal modulation induced by the dipole–dipole interaction between paramagnetic spin ½ particles in pairs embedded in disordered systems has been analyzed comprehensively. It has been shown that the PELDOR signal contains additional terms in contrast to the situation considered in the current theory, when the EPR spectra of the spin labels in the pairs do not overlap. In disordered systems, the pairs of spin labels have the characteristic dipolar interaction frequency. According to the current theory for pairs of spin labels, the PELDOR signal reveals the modulation with this characteristic frequency. The additional terms, which are obtained in this work, do not change the modulation frequency of the PELDOR signal for pairs of spin labels. However, these additional terms should be taken into account when analyzing the amplitude of the PELDOR signal and the amplitude of the modulation of the PELDOR signal. The consistent approach to treating the PELDOR data for the groups containing three or more spin labels has been outlined on the basis of the results for pairs of spin labels. It has been also analyzed how the spin flips and molecular motion or molecular isomerization can affect the manifestation of the interaction between the spin labels in PELDOR experiments. PELDOR experiments for the stable biradicals (biradicals I containing 1-oxyl-2,2,5,5-tetramethylpyrroline-3-yl spin labels and biradicals II containing 3-imidazoline spin labels) have been performed. The results have been interpreted within the theory developed in this work.     

Spin Seebeck effect and spin Hall magnetoresistance in the Pt/Y_3Fe_5O_(12) heterostructure under laser-heating

In the previous study of longitudinal spin Seebeck effect(LSSE), the thermal gradient was often generated by inserting the sample between the cool bath and the hot bath. For practical use, this method is too cumbersome to be easily integrated into modern electrical circuits. Since the laser can be easily focused into a small region, it will be more convenient and friendly to the integrated circuit. In this paper, we systematically investigate the LSSE and spin Hall magnetoresistance(SMR) of the Pt/Y_3 Fe_5 O_(12) heterostructure under focused laser-heating. We find that the extremely large voltage of inverse spin Hall effect(VISHE) can be obtained by reducing the diameter of laser or increasing the number of light spots.Meanwhile, even under the illumination of the ultraviolet light which will excite the electron from the valence band to the conduction band in yttrium iron garnet(YIG), the magnitude of SMR is nearly constant. It indicates that the spin transport behavior of the adjacent Pt is independent of the electron configuration of YIG. The laser-heating method to generate LSSE will be very promising for modern integrated electronic circuits and will promote the application of spin caloritronics in practice.     

界面生长中断对GaAs (111)衬底上 AlGaAs/GaAs量子阱电子自旋寿命的影响

用固源分子束外延技术(SSMBE)在GaAs(111)衬底上,采用不同的界面中断时间生长了多组AlGaAs/GaAs多量子阱样品(MQWs),通过室温发光光谱和时间分辨克尔旋转谱(TRKR)研究了界面生长中断对发光光谱半峰全宽(FWHM)和量子阱中电子自旋弛豫时间(自旋寿命)的影响,发现了自旋寿命随着界面生长中断时间的增加呈现先减小后增加的趋势,此变化趋势与荧光光谱半峰全宽表征的材料质量随中断时间的变化一致,适当的界面生长中断时间能有效的增加GaAs (111)衬底上AlGaAs/GaAs 多量子阱中电子自旋寿命。     

Neutron spectra at 0° from p—p and p—d collisions at 647 and 800 MeV incident energies

The p—d spectra show sharp high-energy peaks (≈ 15 MeV FWHM) with integrated yields of 30 and 31 mb/sr, respectively and with lower-energy bumps associated with pion production. The p—p spectra reflect the influence of the Δ(1232) resonance.     

Controllable beating signal using stored light pulse

We experimentally study the controllable generation of a beating signal using stored light pulses based on electromagnetically induced transparency(EIT) in a solid medium. The beating signal relies on an asymmetric procedure of light storage and retrieval. After storing the probe pulse into the spin coherence under the EIT condition, two-color control fields with opposite detunings instead of the initial control field are used to scatter the stored spin coherence. The controllable beating signal is generated due to alternative constructive and destructive interferences in the retrieved signal intensities. The beating of the two-color control fields is mapped into the beating of weak probe fields by using atomic spin coherence. This beating signal will be important in precise atomic spectroscopy and fast quantum limited measurements.