Loading characteristics of a spin-transfer nano-oscillator

A family of loading and control characteristics of a spin-transfer nano-oscillator (STNO) at various values of direct current have been constructed by integrating the Landau–Lifshitz–Gilbert–Slonczewski equation. The obtained characteristics are compared to approximated dependences calculated using truncated equations with respect to the first harmonic. An approximate expression is derived for the load resistance ensuring the maximum STNO output power.     

Spatial self-filtering with polarizer sheets

A method for phase visualization and edge enhancement by spatial self-filtering by use of a polarizer sheet in the Fourier plane of an optical processor is described. Light absorbed by the polarizer sheet induces a thermal lens, which, in turn, produces selective action on certain spatial frequencies of the image to be processed. Some experiments that demonstrate the self-filtering action of the proposed system are presented.     

A system of phase synchronization of a spin-transfer nano-oscillator

We have studied the dynamics of a filterless phase-synchronization system (PSS) of a spin-transfer nano-oscillator (STNO) generating microwave oscillations in a broad range of frequencies under the effect of direct current and external magnetic field. Bifurcations in the system caused by a change in the frequency detuning of synchronized oscillations are considered. Bands of phase locking and synchronism are determined. The existence of a phase-locking band in the filterless PSS of STNOs basically distinguishes these oscillators from other types of microwave generators.     

刚性包带式星箭连接装置解锁分离过程动力学分析

刚性包带式星箭连接装置能够为重型运载火箭提供更高的星箭连接承载能力,但对其分离释放过程的动力学研究尚未深入.该研究建立刚性包带式星箭连接装置非线性动力学分析模型,采用显式动力学仿真法分析了包带接头分离速度、分离冲击响应和捕获运动规律,研究解锁时间和预紧力等因素对分离与捕获过程的影响规律.结果 表明:延长解锁时间和减小预...     

Direct observation of a propagating spin wave induced by spin-transfer torque

Spin torque oscillators with nanoscale electrical contacts are able to produce coherent spin waves in extended magnetic films, and offer an attractive combination of electrical and magnetic field control, broadband operation, fast spin-wave frequency modulation, and the possibility of synchronizing multiple spin-wave injection sites. However, many potential applications rely on propagating (as opposed to localized) spin waves, and direct evidence for propagation has been lacking. Here, we directly observe a propagating spin wave launched from a spin torque oscillator with a nanoscale electrical contact into an extended Permalloy (nickel iron) film through the spin transfer torque effect. The data, obtained by wave-vector-resolved micro-focused Brillouin light scattering, show that spin waves with tunable frequencies can propagate for several micrometres. Micromagnetic simulations provide the theoretical support to quantitatively reproduce the results.     

Full-field optical coherence tomography by achromatic phase shifting with a rotating polarizer

We demonstrate two-dimensional detection optical coherence tomography (OCT) using achromatic phase shifting with a rotating polarizer. This phase shifting, which experiences a light beam with a cyclic change in its polarization state, is, in principle, independent of wavelength. We simulated the wavelength dependence of an achromatic phase shifter using Jones calculus and found that the achromatic region exceeded 145 nm when the deviation of the phase retardation was less than +/- 0.5 degrees. Using the achromatic phase shifter and a conventional phase-shift calculation method, we obtained en face OCT images of an onion at different depths. This method is effective to enhance the quality of OCT with an ultrabroad-spectrum light source.     

Segmented coupled-wave analysis of a curved wire-grid polarizer

The performance of a wire-grid polarizer (WGP) on a curved surface was investigated with a simple numerical model. The computation model combines rigorous coupled-wave analysis with piecewise linear segmentation that approximates a curved surface for two bending configurations. A curvature-induced Rayleigh anomaly is found to be the main performance degradation mechanism that reduces transmittance and polarization contrast. A WGP on a curved surface is more likely to incur the Rayleigh anomaly with smaller surface curvature. For a given curvature, a larger WGP is more vulnerable. Effects of polar and azimuthal incidence angles were also analyzed. Suggestions were made in regard to a WGP design that minimizes the performance degradation.     

Polarization characteristics of a wire-grid polarizer in a rotating platform

I explore the polarization characteristics of a wire-grid polarizer operating in a rotating platform using well-established rigorous coupled-wave analysis. The results show that the performance of a wire-grid polarizer evaluated in transmittance and extinction ratio is substantially degraded with rotation, although it is still more robust than that of a perfect polarizer. The performance may further deteriorate with inclined incidence due to an increased negative effect of a Rayleigh anomaly. Either a finer or a deeper grating reduces the adverse effect of rotation. Although implementation of such a grating is difficult, the rotation characteristics can be enhanced by means of pixelating the wire grids of various orientations and capturing the input images with a sufficiently high sampling rate.     

Design of a broadband UV-visible alpha-barium borate polarizer

Until recently, the construction of polarizers for operation below approximately 260 nm were limited to materials such as magnesium fluoride and crystalline quartz. These materials have a much smaller birefringence than calcite, but unlike calcite they have good transmission below 200 nm. These materials are, however, not well suited for Glan-Taylor-type polarizer designs, as they do not produce a large angular separation of the polarized components. A new material, a-barium borate, has recently become available, which transmits to just below 200 nm and has a birefringence that approaches that of calcite. We analyze the performance of various polarizer designs that use this material. Results are presented that compare theory with experimental investigation of a manufactured device.     

Fiber-optic polarizer using birefringent crystal as a cladding

A new type of fiber-optic polarizer has been developed in which the birefringent material is formed around the core fiber as a cladding. A NaNO(3) single crystal is used as the birefringent material. The extinction ratios for the polarized light are measured for fibers with cores of various radii and claddings of various lengths. The extinction ratios obtained are typically 31.2 dB for a core diameter of 6 μm and a cladding length of 6 mm.     

Planar optical array with a spatial-integration feature

A planar optical array is presented that provides a selective concentration of the light incident upon the system onto a given area. Several alternative designs are analyzed and explained geometrically. The photometric calculation is presented for three different levels of approximation. A prototype of the proposed system is tested, showing good accordance with the theoretical predictions.     

Compact ellipsometer employing a static polarimeter module with arrayed polarizer and wave-plate elements

A portable ellipsometer with a compact static polarimeter using an arrayed polarizer, an arrayed wave plate, and a CCD image sensor is developed. A high level of repeatability at a measurement speed of 0.3 s is demonstrated by measurement of SiO(2) films ranging from 2 to 300 nm in thickness deposited on an Si wafer. There is the potential to realize an ultracompact ellipsometer module by integrating the optical source and receiver, suitable for deployment in a variety of manufacturing equipment and measurement instruments.     

Spin-torque oscillator using a perpendicular polarizer and a planar free layer

Spintronics materials have recently been considered for radio-frequency devices such as oscillators by exploiting the transfer of spin angular momentum between a spin-polarized electrical current and the magnetic nanostructure it passes through. While previous spin-transfer oscillators (STOs) were based on in-plane magnetized structures, here we present the realization of an STO that contains a perpendicular spin current polarizer combined with an in-plane magnetized free layer. This device is characterized by high-frequency oscillations of the free-layer magnetization, consistent with out-of-plane steady-state precessions induced at the threshold current by a spin-transfer torque from perpendicularly polarized electrons. The results are summarized in static and dynamic current-field state diagrams and will be of importance for the design of STOs with enhanced output signals.     

Performance uniformity analysis of a wire-grid polarizer in imaging polarimetry

The polarimetric performance nonuniformity of a wire-grid polarizer (WGP) used in imaging polarimetry is investigated with a simple numerical model. The simulation results based on rigorous coupled-wave analysis show that the aperture ratio between the entrance pupil and the WGP significantly affects the uniformity among pixels of a WGP. Even with a WGP smaller than an imaging aperture, the results suggest that the design avoids incurring a Rayleigh anomaly, which causes a substantial increase in polarimetric nonuniformity. Minimizing the variation due to the characteristics of a WGP is important to reduce the likelihood of an error in imaging polarimetry.     

Simple method to fabricate a polarizer with a large aperture by the use of anodic alumina films

A simple method is proposed for the fabrication of an optical polarizer with a large aperture by the use of anodic alumina films. The aperture size of the polarizer is 10 × 10 mm(2), the extinction ratio is shown to be larger than 35 dB, and the insertion loss is less than 1 dB at a wavelength of 1.55 μm.     

动态心电图机的检定装置

介绍了一种动态心电图机的检定装置。该装置根据Holter导联连接方式设计导联电极开关控制电路,采用金属外壳屏蔽部分外部干扰信号优化输入阻抗测量。实验结果及测量结果不确定度评定表明该装置能够用于Holter的检定,保证Holter计量性能的准确可靠,为病人身体健康提供保障。     

Time of flight spectrometer with optical polarizer for cold pulsed neutrons

We describe a new TOF spectrometer (named TOP) installed at the pulsed spallation neutron source at KENS. Pulsed neutrons moderated by solid methane (cooled to 20 K) and transmitted by a guide tube were polarized by a Soller array of curved mirrors. The performance and the detailed instrumentation are summarized.     

Increasing the precision of a device used to determine the dynamic coefficient of friction

A theoretical evaluation of the potential application of a device with inclined plane for determining the dynamic coefficient of friction is given. Structural changes in the device that make it possible to increase its precision are proposed. Computational equations for estimating the resolution of the device are presented. __________ Translated from Izmeritel’naya Tekhnika, No. 11, pp. 24–26, November, 2007.