Pulsed Laser Precision Length Measurements

The paper discusses mode locking use in pulsed lasers for precision measurement of large lengths.     

A Pulsed GaAs Laser System for Semiconductor Carrier Lifetime Measurements

An electronic system is described for controlling a semiconductor laser, which is convenient for measuring semiconductor carrier lifetimes of 500 ns or greater by the photoconductive decay method with the laser providing the sample illumination. Particular attention is given to the circuit of the power pulse generator, which was designed to operate the laser above threshold and to provide a means of controlling the output intensity of the laser radiation.     

An All-Digital Self-Calibration Method for a Vernier-Based Time-to-Digital Converter

This paper presents a new calibration method for a Vernier-based time-to-digital converter (TDC). In the proposed method, delay lines in the TDC are configured as on-chip ring oscillators for generating a sequence of time events. These time events are applied to the TDC in the calibration mode, and then, the probability distribution of output codes is determined. The variations of the quantization step and the actual transfer characteristic representing the TDC are estimated through statistical analysis of the output codes. The proposed method eliminates the need for accurate external sources typically used for TDC calibration. Simulation and experimental results using a field-programmable gate array platform indicate that the method can successfully be employed to calibrate high-resolution TDCs with reasonable accuracy.      

Ensuring the Uniformity of Measurements of Spatial-Energy Characteristics of Pulsed Laser Radiation

Measurement Techniques - The structure and principle of creation of a standard for the spatial-power characteristics of pulsed laser radiation are examined, and problems solved with its aid are...     

Aircraft Wake Vortex Detection and Measurement with Pulsed Solid-state Coherent Laser Radar

Abstract

Pulsed solid-state coherent laser radar (lidar) systems can measure radial wind velocity to precisions well below 1 m s^?1 at spatial scales on the order of 30–50 m and to ranges of several kilometres. This capability is appropriate for a variety of measurement objectives in the airport terminal area. Wake vortex detection and tracking is one of the primary objectives currently being evaluated by regulatory agencies in the United States and elsewhere. Up to now, non-invasive measurement of wake vortex properties has been limited to short-range continuous-wave lidar systems. This paper discusses this application and presents theoretical analysis and experimental results for pulsed 2 μm coherent lidar. Detection, tracking, and measurement results are presented for sample DC10, 757, and 727 aircraft landings from a laser radar wake vortex database compiled in 1993 at Denver Stapleton International Airport.     

激光干涉仪与纳米精度检测

文章对光外差、移相、正弦相位调制等几种常见的纳米精度干涉测量技术进行了综述 ,并介绍了上海光机所的相关工作 .     

Low-Frequency Parametric Amplifier for Small Voltage Measurements

This paper analyzes the low-frequency parametric amplifier, which, in opposition to the parametric amplifiers in the high-frequency range, is wide band and can be realized only simultaneously as an upper and lower sideband up-converter. Three derived basic equations give the possibility of drawing equivalent circuits, in order to calculate gain and stability conditions. The influence of detuning on characteristics of amplifiers is analyzed and investigated experimentally. Cascading more stages of parametric amplifiers is meaningless. The best results can be obtained when the second stage is an upper sideband up-converter. LF parametric amplifiers enable us to achieve a low noise (<0.3 ?V for 100-Hz bandwidth), free from flicker noise, a high input resistance and a high common-mode rejection ratio. For this reason, the amplifier can be applied as the measuring preamplifier of brain voltages.     

A New Resistance-to-Frequency Converter for Temperature Measurements in Calorimeters

A circuit is described for the measurement of the temperature difference between input and output heat exchangers by means of resistance thermometers. Two thermometer resistors form part of a resistance-to-frequency converter, the frequency being proportional to their difference in resistance value. The frequency is also dependent on a few additional resistors and a capacitor. Drifts and offsets of amplifiers are eliminated to a first order. No stabilized voltages are used. The circuit was developed as part of a simple and reliable calorimeter for domestic uses.     

All-Fiber Multifunction Continuous-Wave Coherent Laser Radar at 1.55 num for Range, Speed, Vibration, and Wind Measurements

The design and performance of a simple, multifunction 1.55-mum continuous-wave (cw) and frequency-modulated cw coherent laser radar system with an output power of 1 W is presented. The system is based on a semiconductor laser source plus an erbium-doped fiber amplifier, a polarization-independent fiber-optic circulator used as the transmit-receive switch, and digital signal processing. The system is shown to be able to perform wind-speed measurements even in clear atmospheric conditions when the visibility exceeds 40 km. The aerosol measurements indicate the potential to use single-particle detection for wind measurements with enhanced sensitivity. The system can perform range and line-of-sight velocity measurements of hard targets at ranges of the order of several kilometers with a range accuracy of a few meters and a velocity accuracy of 0.1 m/s by use of triangular-wave frequency modulation with compensation of the frequency-modulation response of the semiconductor laser. The system also demonstrates a capability for vibration sensing.     

Thermal Converters for Audio-Frequency Voltage Measurements of High Accuracy

The ac-dc differences of a reference group of thermoelements have been evaluated at audio frequencies to a few parts per million (ppm) at currents from 5 to 20 mA. A technique for comparing the ac-dc differences of two thermoelements with an uncertainty of about 2 ppm has been developed. Two 5 mA thermoelements are used with a plug-in set of resistors of computable reactances to form thermal voltage converters for voltage measurements. With this same technique adjacent ranges of these converters can be compared to step up from 0.5 to 500 V to better than 10 ppm.     

A System for Accurate Direct and Alternating Voltage Measurements

A system for calibrating and using a group of dc and ac standards has been developed at NBS to meet increasing needs for greater accuracy in the measurement of direct and rms alternating voltages at audio frequencies. With a group of saturated cells, a universal ratio set as a potentiometer, a simplified self-calibrating volt box, and a new differential-thermocouple ac-dc comparator, an accuracy of 10 ppm can be obtained for direct voltage measurements and 40 ppm for rms alternating voltage measurements between 20 and 20 000 c/s, in terms of the direct volt and the ac-dc transfer standards maintained at NBS.     

Synthesis of Airborne Laser Measurements for Navigation Algorithms

Airborne laser scanners are widely used for remote sensing and mapping and they are recently being applied to navigation of aerial and ground vehicles. Evaluation of new navigation algorithms in the presence of varying platform, sensor, and environment parameters requires high-fidelity measurement models of the airborne laser sensor. We present a procedure for the synthesis of airborne laser scanner measurements using aircraft flight trajectory, the scanner's mechanical and optical characteristics and the target environment model.     

用于对空探测的激光成像雷达设计

本文提出了线阵扫描式激光成像雷达的组成方案,对激光发射、成像接收、分析处理等各个分系统的设计方法进行了详细探讨.以此为依据并且充分考虑了各种参数之间的相互关系,设计出一个原型系统.该系统采用32维APD线列器件,工作波长1.064μm,扫描机构为一维振镜.     

Cryogenic Voltage Comparator System for 2e/h Measurements

The design and operation of a cryogenic voltage comparator system for precision 2e/h measurements is described. Major improvements embodied in the new 2e/h system include the use of 1) a single microstripline-coupled Josephson tunnel junction to obtain usable step voltages up to 10 mV at 10.0 GHz, 2) a cryogenic voltage divider comprised of two resistors whose ratio is calibrated with a low-temperature dc current comparator, 3) a superconducting quantum interference device (SQUID) null detector, and 4) superconducting switching. The accuracy of the present 196:1 divider system is estimated to be about 2 parts in 108 on the basis of preliminary tests and is limited by resistor self-heating during calibration.     

A Semi-analytic Approach for Coherent Laser Radar System Efficiency

Abstract

A nearest Gaussian approximation (NGA) is proposed to approximate any shape for a single mode laser beam by a Gaussian shape. The application considered is a determination of the system efficiency in heterodyne coherent laser radar (HCLR). For an actual beam its NGA is defined by three parameters: the waist spot size and location, and an amplitude coefficient. These parameters are computed by a maximization of the norm of the scalar product written for the actual and Gaussian beams. In the case of the truncated Gaussian beam, particularly relevant to HCLR, the waist location can be analytically calculated, and only two parameters remain unknown: the waist spot size and amplitude coefficient. Using numerical applications, it is shown the NGA is in good agreement with Fresnel integral solution. The NGA combines a good accuracy and capability of analytical solutions. It can treat a variation in system efficiency owing to a misalignment angle between the transmitter and local oscillator.     

用PLD法制备声表面波器件用ZnO薄膜

采用脉冲激光淀积 (PLD)法在单晶Si(10 0 )衬底上淀积了ZnO薄膜。XRD、TEM和AFM分析表明 ,淀积的ZnO薄膜具有良好的c轴取向性和表面平整度。通过改变淀积气氛或在纯氧中高温退火 ,ZnO薄膜的电阻率提高到 10 7Ω·cm。这些结果表明 ,用PLD法淀积的ZnO薄膜能够满足声表面波(SAW )器件的需要。     

An AC Josephson Voltage Standard for AC–DC Transfer-Standard Measurements

We describe the traceability chain of length measurements at Centre for Metrology and Accreditation (MIKES) from atomic clocks to the lasers of primary interferometers. Crucial part of the traceability chain, an optical frequency comb generator linking optical frequencies to atomic clocks, is described in detail. The frequency comb generator is used in frequency calibrations of iodine-stabilized lasers, which are operated in compliance with the recommendations of the practical realization of the definition of the meter. Measured absolute frequencies of iodine-stabilized lasers, time records of the measurements, and the respective Allan deviations demonstrate the solid performance of the MIKES laser frequency standards. The results are in good agreement with the recommended values, as well as with the independent characterizations of the measured lasers