A digital signal conversion system for astronomy radio interferometers with small antennas

Results of designing a digital signal conversion system for radio interferometers with small-diameter (up to 12 m) antennas are presented. The system contains four digital signal conversion channels with 500-MHz bandwidths. The output data stream rate in the VDIF format is 2048 Mbit/s per channel, and the cumulative output data flow is 8192 Mbit/s. The observation data flows arrive at the signal recording buffer unit and can be transmitted from there via a 10G Ethernet interface to a correlator in near-real time.     

A Data Acquisition System for Very-Long-Baseline Interferometers

A data-acquisition system designed for very-long-baseline interferometers is connected to the outputs of cryoelectronic radio astronomy receivers, selects signals in specified frequency bands, and converts them into digital data flows for their recording or transmission through telecommunication channels. The system has two inputs and may contain from two to eight base-band converters with an intermediate frequency tuning range of 100–1000 MHz with a 10-kHz step. These converters transform input signals into video frequencies (up to 16 MHz) and separate signals of the upper and lower side bands with an image rejection of >23 dB. The distortions and loss in the phase coherence of the received noise signals are minimized thanks to the equalizing of the amplitude and phase responses of the amplifiers and selectors, and the good spectral characteristics of the local oscillators of the base-band converters. The data-acquisition system is controlled by a PC or the Mark IV Field System program (now used internationally in the pursuit of radio interferometry), which is installed in the radio telescope's central computer using an RS-232 interface. The prototype of such a system is used as standard equipment for conducting observations on the Svetloye–Zelenchukskaya radio interferometer. The first lot of such systems for the development of a network of radio interferometers has been produced.     

Multi-probe scanning system comprising three laser interferometers and one autocollimator for measuring flat bar mirror profile with nanometer accuracy

This paper describes a multi-probe scanning system comprising three laser interferometers and one autocollimator to measure a flat bar mirror profile with nanometer accuracy. The laser interferometers probe the surface of the flat bar mirror that is fixed on top of a scanning stage, while the autocollimator simultaneously measures the yaw error of the scanning stage. The flat bar mirror profile and horizontal straightness motion error are reconstructed by an application of simultaneous linear equations and least-squares method. Measurement uncertainties of the flat bar mirror profile were numerically evaluated for different installation distances between the laser interferometers. The average measurement uncertainty was found to be only 10 nm with installation distances of 10 and 21 mm between the first and second, and first and third interferometers, respectively. To validate the simulation results, a prototype system was built using an X–Y linear stage driven by a stepper motor with steps of 1 mm along the X direction. Experiments were conducted with fixed interferometers distances of 10 and 21 mm, as in the simulation, on a flat bar mirror with a profile known to an accuracy of λ = 632.8 nm. The average value of two standard deviations (95%) of the profile calculated over ten experiments was approximately 10 nm. Other results from the experiment showed that the system can also measure the yaw and horizontal straightness motion errors successfully at a high horizontal resolution. Comparing with the results measured by ZYGO's interferometer, our measured data excluding some edge points showed agreement to within approximately 10 nm. Therefore, we concluded that our measurement profile has an accuracy in the nanometer range.     

Results of testing a radio interferometer with digital signal processing in a 400-MHz band

Results of testing the astronomical radio interferometer at the Svetloe-Zelenchukskaya observatory using digital signal processing channels with 400-MHz bands are presented. Observation data were recorded in the VDIF format with a 2048-Mbit/s rate by the Mark 5C terminal. Simultaneously, data obtained using the standard equipment of the Quasar complex were recorded. The observation results were processed by both the DiFX experimental software correlator and APK standard correlator, which is a part of the Quasar complex. Due to the used wideband data acquisition system, the sensitivity of the radio interferometer went up by a factor of 4.7–4.8, and the accuracy of determining the time position of the correlation response increased by a factor of 1.6. The experiment confirmed the efficiency of the new wideband digital data acquisition system and possibility of its applications in astronomical radio interferometers with small (～13 m) antennas.     

A fully stabilized Brillouin spectrometer with high contrast and high resolution

Using a triple-pass plane and a confocal Fabry-Pérot interferometers in tandem, we have constructed a Brillouin spectrometer with a frequency resolution of 10(8) and a contrast of more than 10(10). Our system is controlled and fully stabilized by a desktop calculator, allowing efficient data collection for very long integration times.     

基于FPGA的数据采集系统中20MHz模拟通道设计

数据采集系统就是为了完成数据采集过程,由为了完成某些特定信号或一组信号而由一系列软件和硬件组成的软硬件系统.模拟通道作为数据采集系统中的关键部分组成部分之一,其性能指标直接制约了数据采集系统的发展,如何使模拟通道具有更高的带宽,更好的交直流性能,更低的噪声,成为了数据采集系统中模拟通道设计研究的主要内容和关键内容.     

A 24-Bit Data Acquisition System

A 24-bit data acquisition system is developed for recording and processing seismic signals. The system contains a 24-channel analog-to-digital converter and controlling microcontroller. Data accumulation and processing is carried out by a personal computer to which the data acquisition system is connected via an RS-232 channel and high-speed synchronous channel.     

A Data Stream Converter for a Radio Telescope with a Wideband-Signal Digital Recording System

A data-stream converter makes it possible to connect a radio telescope with wideband (512 MHz) signal-recording channels to active very-long-baseline interferometers using multichannel recording systems for narrowband (16 or 8 MHz) signals. A digital converter based on a field programmed gate array (FPGA) selects and formats up to 16 narrowband signals.     

计量型原子力显微镜的位移测量系统(英文)

针对纳米结构表征和纳米制造的质量控制需要,中国计量科学研究院设计并搭建了一台计量型原子力显微镜用于纳米几何结构的测量.为了将位移精确溯源到国际单位米,研制了单频8倍程干涉仪测量位移,样品表面形貌则由接触式原子力显微镜测量.一个立方体反射镜与原子力显微镜的测头固定,作为干涉仪的参考镜.两个互相垂直的干涉仪用于测量样品与探针在x-y方向的相对位置.样品台置于具有三面反射镜的零膨胀玻璃块上,由压电陶瓷位移台驱动.另外两台干涉仪测量样品与探针在z方向的位移,探针针尖位于干涉仪光束的交点以减小Abbe误差.由于光学器件的缺陷产生的相位混合会引起非线性误差,采用谐波分离法拟合干涉信号来修正误差,修正后干涉仪测量误差减小为0.7 nm.     

A source of a reference spherical wave based on a single mode optical fiber with a narrowed exit aperture

A new type of a reference spherical wave source (SWS) based on a single mode optical fiber with a narrowed down up to the submicrometer size exit aperture is proposed. It is intended for the precision point diffraction interferometers as a source of a reference wave. Systematic experimental errors which influence the measurement accuracy of the quality of the wave fronts generated by the SWSs are considered. Experimental data on wave front deformations are given. The combined root-mean-square (rms) wave deformation for a couple of the SWSs measured in a numerical aperture of NA=0.27 reaches the value of rms=0.36 nm that corresponds to rms=0.25 nm of a single SWS or about lambda2500 for the red He-Ne laser.     

Microcomputer stabilization of a Fabry-Perot interferometer

Fabry-Perot interferometers typically require some form of active stabilization system for long-term operation. A stabilization system based on a microcomputer is described which is able to maintain the finesse of a plane parallel Fabry-Perot interferometer for long periods of time. The microcomputer takes the place of the multichannel analyzer, ramp generator, and stabilizer of a conventionally stabilized system. Sample data illustrating the operation of the system on the Brillouin spectrum of fused silica, with and without computer corrections, are included.     

Pressure drop measurement in microfluidics channel by the Fabry-Perot diaphragm-based flow sensor

The measurement and control of pressure is an important parameter in optimizing flow rates in microfluidic channels. In this paper, we present simulation and experimental results of measuring pressure drop in a rectangular microfluidics channel by two Fabry-Perot (FP) flow sensors. Sensors include two circular diaphragms made of PDMS (Polydimethylsiloxane) with 50 μm thickness and 200 μm radius, located 2 cm apart which the surface of them create FP cavity with end surface of the fiber optic. Fabry-Pérot interferometers above two diaphragms measure the different deflections of the diaphragms caused by pressure changes in the micro channel. The fluid-structure interaction method is used to solve three-dimensional (3D) Navier-Stokes and continuity equations for selecting appropriate diaphragm thickness and validating experimental results. The experimental and theoretical results are in good agreement and according to the experimental results, these sensors have sensitivities of 30 (nm. (μL/min)^-1) and 10 (nm. (μL/min)^-1) without hysteresis and the resolution of the sensor is 33 nL/min.     

Active noise cancellation in a suspended interferometer

We demonstrate feed-forward vibration isolation on a suspended Fabry-Perot interferometer using Wiener filtering and a variant of the common least mean square adaptive filter algorithm. We compare the experimental results with theoretical estimates of the cancellation efficiency. Using data from the recent Laser Interferometer Gravitational Wave Observatory (LIGO) Science Run, we also estimate the impact of this technique on full scale gravitational wave interferometers. In the future, we expect to use this technique also to remove acoustic, magnetic, and gravitational noise perturbations from the LIGO interferometers. This noise cancellation technique is simple enough to implement in standard laboratory environments and can be used to improve signal-to-noise ratio for a variety of high precision experiments.     

电缆局部放电数据采集系统的设计

高电压电缆局部放电严重影响电缆的寿命和供电可靠性。电缆局部放电信号微弱,特征信号频率高达300MHz,具有电容式和电感式两种传感器,采样点多,数据采集难度大。采用美国国家仪器有限公司生产的多路选择板卡PXI2593、PXI5154高速数据采集板卡及其相关的计算机系统,作为高压电缆在线监测系统的数据采集硬件平台,设计数据采集通信子系统和客户端子系统,实现采样通道选择、数据采集和存储、采样数据显示、历史数据回放、信息参数配置与用户信息管理。     

适用于光黏工艺的干涉仪公差保证方法

空间干涉测量系统是空间引力波探测的重要组成部分。本文介绍了一种全玻璃材料的差频激光干涉仪的组成结构和工作原理,对差频干涉仪中双相干光束的匹配对准难题,介绍了一种适用于光黏装配工艺的角度公差和位置公差保证方法。这种方法采用了监测系统和微量调整机构相结合的方式,首先,监控系统可以实现光线相对位置的实时测量,给出被调整光线的调整方向和调整量;然后,微量调整机构可以在平面移动和轴向转动3个自由度上,对目标器件实现微米量级的微量调整;监控过程和调整过程反复迭代,可实现对光学元器件的高精度位置控制和角度控制。实验结果表明,在调整方向上角度公差优于80μrad,位置公差优于85μm。本方案基本满足差频激光干涉仪的装配精度需求,为后续更高精度的装配奠定基础。     

Interferometric measurement of angles

The laser interferometers for angle measurement in a wide range have been presented. These are the systems based on the modified Twyman-Green interferometer principle, constructed and tested by the author. Each modification is aimed at the optimum configuration, which should combine high accuracy and wide range simultaneously. Starting with the simple interferometer, through its various versions with beam shift compensation and diametrically placed reflectors, to the set-up which has a measuring range of 2π rad and rotational positioning of 0.04″. The final system is designed for automatic measurement of angular positions and for checking the angle standards. The error analysis common to all interferometers with rotating reflector is given.     

面向轿车整车设计的DSS系统结构和数据仓库建模技术研究

基于历史案例建立面向整车设计的决策支持系统是轿车虚拟制造中的重要环节。数据仓库，联机分析和数据控制技术可以为其提供有效的解决途径。提出了面向轿车整车设计的DSS系统结构，以及数据仓库的主要建模步骤和关键数据结构设计，建立了关键的数据仓库应用逻辑模型。     

The measurement of creep of elgiloy springs with a balanced interferometer

Elgiloy is a cobalt alloy that is commonly used as the material of analog clock springs. The rotational creep of loaded ‘clock’ springs made of elgiloy, as measured with a balanced interferometer, is described. For the measurements described here, the spiral clock springs are supported on a radial air bearing and wound up to support the nominal torque load required in the actual application. Two linear interferometers measure displacements of retroreflectors attached to the spring, and rotational creep is calculated by the ratio of the difference between the displacements and the distance between the retroreflectors. Environmental disturbances are nominally cancelled through the difference in the displacements measured by the interferometers at the same distance from the retroreflectors.     

Correction of Errors in Polarization Based Dynamic Phase Shifting Interferometers

Polarization based interferometers for single snap-shot measurements allow single frame, quantitative phase acquisition for vibration insensitive measurements of optical surfaces. Application of these polarization based phase sensors requires the test and reference beams of the interferometer to be orthogonally polarized. As with all polarization based interferometers, these systems can suffer from phase dependent errors resulting from systematic polarization aberrations. This type of measurement error presents a particular challenge because it varies in magnitude both spatially and temporally between each measurement. In this article, a general discussion of phase calculation error is presented. We then present an algorithm that is capable of mitigating phase-dependent measurement errors on-the-fly. The algorithm implementation is non-iterative providing sensor frame rate limited phase calculations. Finally, results are presented for both a high numerical aperture system, where the residual error is reduced to the shot noise limit, and a system with significant birefringence in the test arm.