Employing a Cerenkov detector for the thickness measurement of X-rays in a scattering background

The variation in environmental scattering background is a major source of systematic errors in X- ray inspection and measurement systems. As the energy of these photons consisting of environmental scattering background is much lower generally, the Cerenkov detectors having the detection threshold are likely insensitive to them and able to exclude their influence. A thickness measurement experiment is designed to verify the idea by employing a Cerenkov detector and an ionizing chamber for comparison. Furthermore, it is also found that the application of the Cerenkov detectors is helpful to exclude another systematic error from the variation of low energy components in the spectrum incident on the detector volume.     

High Power THz Undulator Radiation from Linear Accelerator

A 30-MeV femto-second electron linac is built at the Shanghai Institute of Applied Physics, which can produce high power, coherent THz undulator radiation. We report the experimental facility and measurement of the power, frequency spectrum. First experiments show the averaged power at THz to be about 20mW.     

Methods for measuring pedestrian density, flow, speed and direction with minimal scatter

The progress of image processing during recent years allows the measurement of pedestrian characteristics on a “microscopic” scale with low costs. However, density and flow are concepts of fluid mechanics defined for the limit of infinitely many particles. Standard methods of measuring these quantities locally (e.g. counting heads within a rectangle) suffer from large data scatter. The remedy of averaging over large spaces or long times reduces the possible resolution and inhibits the gain obtained by the new technologies.In this contribution we introduce a concept for measuring microscopic characteristics on the basis of pedestrian trajectories. Assigning a personal space to every pedestrian via a Voronoi diagram reduces the density scatter. Similarly, calculating direction and speed from position differences between times with identical phases of movement gives low-scatter sequences for speed and direction. Finally we discuss the methods to obtain reliable values for derived quantities and new possibilities of an in-depth analysis of experiments. The resolution obtained indicates the limits of stationary state theory.     

Research on laser Doppler velocimeter for vehicle self-contained inertial navigation system

An idea of using laser Doppler velocimeter (LDV) to measure the velocity for the vehicle inertial navigation system was put forward. The principle of measuring its own velocity with laser Doppler technique was elaborated and reference-beam LDV was designed. Then Doppler signal was processed by tracking filter, frequency spectrum refinement and frequency spectrum correction algorithm. The result of theory and experiment showed that the reference-beam LDV solved the problem that dual-beam LDV cannot be used for measuring when the system was out of focus. Doppler signal was tracked so that signal-to-noise ratio was improved, and the accuracy of the system was enhanced by the technology of frequency spectrum refinement and correction. The measurement mean error was less than 1.5% in velocity range of 0-30 m/s.     

A new method of non-contact gauge block calibration using a fringe-counting technique: I. Theoretical basis

A new non-contact interference method for gauge block or length bar calibration is presented. A central interference fringe of polychromatic light is used for the determination of the end surface position of the measured artefact. Distances referring to these positions are measured using a fringe-counting technique, with a wavelength-stabilized laser interferometer. Absolute and comparative measurement methods are proposed. A new technique for central interference fringe detection and identification is discussed.     

Light intensity modulation fiber-optic sensor for curvature measurement

A light intensity modulation fiber-optic sensor, which can measure curvature directly, has been developed. It is suitable for the measurement of thin, embedded or highly flexible structures. An experimental analysis on the static and dynamic characteristics of sensor has been undertaken. The results show that the output voltage has polarity and a good linear relationship with curvature when the curvature radius is larger than 60 mm. The mathematical model relating the relative output loss, parameters of sensitive zone’s configuration (depth, number, height and half angle of tooth) and bending radius is described analytically based on the geometric optics. Curvature fiber-optic sensors can be used to build a quasi-distributed fiber-optic sensor system, which can measure curvature and torsion angle simultaneously.     

Quantum state sharing with a genuinely entangled five-qubit state and Bell-state measurements

We construct several distinct schemes for tripartite Quantum state sharing (QSTS) of arbitrary single- and two-qubit states. Our schemes use genuinely entangled five-qubit state that has recently been introduced by Brown et al. [J. Phys. A 38 1119 (2005)] as the quantum channel. The Bell-state measurements and the single-qubit measurement are needed in our schemes. In comparison with the QSTS scheme using the same quantum channel [Phys. Rev. A 77 (2008) 032321], not joint measurement, which makes this scheme simpler than the latter.     

Measurement of subpicosecond optical waveforms using a resonator-based phase modulator

We propose a method for the measurement of periodic optical waveforms based on the use of an electrooptic phase modulator placed in an optical Fabry-Perot or ring resonator. Significant broadening of the modulation spectrum extends the recently developed method of periodic modulation for pulse characterization into femtosecond scales. We numerically demonstrate the characterization of a 300-fs optical pulse. We also present a technique based on the temporal fractional Talbot effect for restoration of the pulse phase profile. After fast linear processing, subpicosecond pulses will be observed on the screen of a real-time oscilloscope. This complete characterization of optical pulses is entirely linear and therefore highly sensitive and simple in implementation.     

Distributed strain measurement using a tellurite glass fiber with Brillouin optical correlation-domain reflectometry

A tellurite glass fiber with a high Brillouin gain was employed for distributed strain measurement with Brillouin optical correlation-domain reflectometry (BOCDR). First, the spatial resolution of BOCDR was evaluated using the tellurite fiber. With the high Brillouin gain of the fiber, it was confirmed clearly in the experiment that the spatial resolution is limited by the Rayleigh scattering-induced noise. Then, the dependence of the Brillouin frequency shift (BFS) on strain in the tellurite fiber was investigated, showing a negative dependence with a coefficient of −0.023 MHz/με. Using this tellurite fiber, the distribution of the BFS around a 1-cm strain-applied section was successfully measured with BOCDR of a nominal spatial resolution of 6 mm.     

Interpolation algorithm for recovering the missing phase values in 3D measurement

In the three-dimensional (3D) phase measurement, some marks are usually adhered to the object in order to make the 3D registration process faster and easier. As covered with marks, local phase data are missing and have to be interpolated later. Considering the phase distribution nearby the marks, a gradient estimate (GE) interpolation algorithm is provided here. This algorithm recovers one pixel's missing phase value with the average of the estimated values which is calculated by gradients in eight directions nearby. Since this algorithm is a local processing, the missing phase values should be interpolated from the edge of the marks to the center. In the computer simulation and the practical experiment, compared with the same-size neighborhood mean (NM) algorithm and the Gerchberg-Saxton (GS) algorithm, this new algorithm achieves very good fit results with the least time. So it can be used as a practical tool for automatic missing phase interpolation.