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The 4th International Symposium on Instrumentation Science and Technology (ISIST'2006) was held in Harbin, China in August 2006. It included sessions on all aspects of the theory, design, test and application of measurement technologies and instruments. The bulk of the Symposium papers, after peer review, have been published by IOP Publishing in the Journal of Physics: Conference Series; a number of papers were selected for publication in Measurement Science and Technology and we hope that readers will find these give a valuable insight into the key topics of the conference.

We describe a single-shot birefringence measurement using a radial polarizer fabricated by a direct atomic force microscope nano-stroking method. A radial polarizer, which converts linearly polarized light into radial polarized light, was prepared by radially aligning liquid crystal molecules in a 150 × 150 µm² region. The birefringence of a calibrated sample is measured by performing image analysis of the sample illuminated by radial polarized light. The measured retardation and the azimuth angle of the calibrated sample almost agreed with the setting values. This method is effective for measuring a temporal change in birefringence.

The present status and the future prospects of the levitation mass method (LMM), which has been proposed and developed by the author as a precision mechanical measurement method and has been applied to dynamic force calibration and material testing, are reviewed. In the LMM, the inertial force of a mass levitated using a pneumatic linear bearing is used as the reference force applied to the objects under test, such as force transducers, materials or structures. The inertial force of the levitated mass is measured using an optical interferometer. As an example, mechanical responses of a gel block against small impact loads were evaluated using the LMM.

This paper presents a review of medical and biological applications of optical fibres, which span a wide range from light-pipes and pressure or displacement sensors through to complex chemical sensors. Coherent fibre bundles are needed for endoscopic imaging whilst single fibres may be used in both near infrared tomography and optical coherence tomography. Delivery of light to tissues, for example to activate targeted chemo-therapeutic agents (PDT), is also achieved conveniently with fibres. Chemical sensing can simply be achieved by transporting light to and from a measurement site with a plain fibre light guide for spectrophotometric or fluorimetry analysis. A further family of fibre-optic chemical sensors has either surface attached molecular recognition sites or a reaction chamber for achieving specific molecular detection. These chemical sensors may be based on the principles of surface plasmon resonance, interferometry, spectrophotometry or fluorimetry. Biological recognition with enzymes or antigen–antibody binding are used to achieve high specificity. The range of potential target molecules has increased rapidly over recent years from simple gases and ions through to large molecules such as DNA.

A method of fabricating nanometre scale multiple linewidth standards based on multilayer thin film deposition techniques is presented. Three layers of chromium (Cr) thin films and three layers of silicon nitride (Si₃N₄) thin films were alternately deposited on a silicon substrate in the radio frequency (RF) magnetron sputtering system and the low-temperature plasma enhanced chemical vapour deposition (PECVD) system. The deposition thicknesses of the Cr thin films are equal to the desired linewidths. The silicon substrate was then cut into small pieces, and the cross-section of each piece was metallographically polished. Perpendicular to the cross-section Si₃N₄ was etched with reactive ion etching (RIE) and nanometre scale multiple linewidth samples with nominal linewidths of 20 nm, 25 nm and 35 nm were fabricated. The fabricated samples were characterized with a scanning electron microscope (SEM). The line edge roughness (LER) and the linewidth roughness (LWR) of the lines of the fabricated samples were evaluated by an offline image analysis algorithm. The lines of the fabricated samples have uniform attributes and good linearity over hundreds of microns. The results show that the presented method is a promising method for the fabrication of nanometre scale multiple linewidth standards.

Stylus scanning remains a crucial method in surface micro- and nano-topography measurement. Its accuracy, especially at shorter wavelengths, depends on the relation of the stylus geometry to surface parameters. We present a 3D computer simulation of measuring non-Gaussian random surfaces with arbitrary tip shapes, studying both the surface distortion and the stylus contact distribution. After a brief discussion of the surface generation and geometrical contact algorithms, this paper concentrates on examples of symmetrical styli having characteristic sizes not much smaller than the surface correlation lengths. It thus attempts to examine the breakdown region as we seek to measure finer topographies. The measuring error appears to be generally smaller with a three-pyramid stylus than with other styli as limits are approached. Perhaps counter-intuitively, the errors in common parameters on surfaces of a similar correlation length and roughness amplitude can be smaller when their kurtosis is high, a condition that might become more common with deliberately imposed nanostructuring.

In order to analyse the Fraunhofer diffractive characteristics of a tilted metallic mesh for its effect on optical measurement, a model is built for Fraunhofer diffraction optical intensity distribution using Huygens–Fresnel diffraction theory; a stretch factor is introduced to represent the stretching of diffraction spots along axis x, as a result of variation in the effective area of a clear aperture after mesh tilting, and an offset factor is introduced to represent the asymmetrical distribution of diffraction spots caused by mesh tilting and the distance between the centre of zero-order diffraction and the observation point. The diffraction characteristics of the tilted mesh are in good agreement with experimental results, which proves the correctness of the model established for it. The location of the centre of zero-order diffraction does not change with θ in an aerial optical measurement, and an increase by 1/cos(θ) times its primary maximum radius along axis x due to the prevailing stretch factor causes a decrease in the resolution of an optical system by the same magnitude. The model established for a tilted mesh can also be used to remove any error due to a tilted slot during slot width measurement.

This paper presents two micro/nano level displacement sensors, which consist of a mini LDGI (linear diffraction grating interferometer) and a focus probe. These two sensors are integrated into the spindle system of a micro/nano-CMM. This micro/nano spindle system is fixed on a rectangular granite bridge to achieve the z-axis function. The motion of the spindle is driven by an ultrasonic motor on a precision cross-roller slide. Its displacement is fed back by the LDGI. A DVD pick-up head is modified with its S-curve principle as the non-contact focus probe. Mounting the probe onto the spindle head, it is possible to achieve a large displacement and nanoresolution measuring spindle system with a feedback nanomotion control scheme. After accuracy calibration and error compensation, the spindle motion to 10 mm can perform 10 nm positioning accuracy and 30 nm measurement accuracy. Experiments on some ultraprecision profiles have shown the capability of this spindle system.

In this paper, two optical techniques, namely, electronic speckle pattern interferometry (ESPI) and fringe projection, are described for the measurement of a low-frequency vibrating object. The combination of optical interferometry and temporal phase analysis allows the measurement on a continuously deforming object without the spatial phase unwrapping process. A series of speckle or fringe patterns is captured by a high-speed CCD camera, and the intensity variation of each pixel on the recorded images is analysed along the time axis using the temporal wavelet transform method that has the property of adaptive band-pass filtering of a measured signal. However, the wavelet transform method is unable to determine the sign of a phase and it is difficult to analyse a part of the object that is not moving. The sign ambiguity problem can be overcome by adding a temporal carrier in the image acquisition process. In the ESPI, a temporal carrier is introduced by a PZT stage in the reference beam of the interferometer. In the fringe projection technique, a laterally shifted fringe pattern is projected on a vibrating object. After the temporal carrier is removed, the absolute displacement of a vibrating object is obtained without the need for a temporal or spatial phase unwrapping process.

In order to evaluate the phase modulation performance of a 256 × 256 pixel reflecting liquid crystal spatial light modulator purchased from the US Boulder Nonlinear Systems, we identify the linear range of phase shift and evaluate the spatial nonuniformity of the modulator by measuring both phase and intensity with a Twyman–Green interferometer. Experimental results show that the 50–210 grey scales linear ranges of the phase shift established by phase and intensity measurements are in good agreement with each other, which proves that more accurate phase modulation can be achieved. The inherent backplane curvature of the modulator is less than λ/3 and the root-mean-square value of the phase nonuniformity across the modulator aperture is less than λ/10, so the backplane curvature of the modulator is the main contributor to phase distortion due to the modulator. Analysing the deviation of the root-mean-square value of the phase nonuniformity indicates that the stability of the modulator decreases with increasing grey scales. It is therefore concluded that the modulator calibrated using a single interferometer can be used for beam steering, wave-front correction and transformation.

Automatic dimensional inspection of 3D articles with high resolution and productivity is an urgent problem for industry and science. Using optical inspection methods, it is essential to take into account the influence of 3D bodies' extension on their Fraunhofer diffraction pattern and images. This influence strongly depends on the configuration of illumination, which therefore is fundamentally important. The previously suggested constructive method, based on the model of equivalent diaphragms, for calculation of diffraction phenomena by 3D bodies of constant thickness was developed for inclined plane and spherical illuminating waves. The equations describing the spatial spectra of a volumetric asymmetric edge and a 3D slit under plane inclined wave illumination have been obtained in analytical form. It was shown that the cross-selection of front and back faces of the volumetric slit occurs in the case of inclined illumination. The solution for diffraction phenomena by a volumetric slit under spherical wave illumination has been represented. In this case the simultaneous selection of either front or back faces of the 3D slit takes place. The obtained results can be applied for investigation of formation and high-frequency filtering images of 3D bodies of constant thickness.

An atomic force microscope (AFM) head designed for nanometrology is accomplished in this study. It is the sensing component of the nano-measuring machine, a nanometrological instrument with a working range of 50 mm × 50 mm × 2 mm, as well as a part of the metrological system of the instrument. Three reference mirrors are mounted on the head and arranged without Abbe error. Relative displacement of the AFM head and the specimen is measured by interferometers and results are traceable. The optical beam deflection method is used to detect the atomic force. The laser beam is introduced through a single-mode polarization-maintaining optical fibre from an external laser diode. With a compact design, a 100 mm optical lever is realized inside the AFM head that is less than 20 mm in thickness and 200 g in weight. A force–distance curve is obtained using a gauge block in a test. Furthermore, online tests of the measurement of a step scale have been made. According to the calculation and experimental verification, the resolution of our AFM head reaches 0.05 nm.

The study of the dynamic characteristics of MEMS micro-devices depends on relevant testing facilities. Testing with a base excitation method was studied and employed in practical tests. A system for the dynamic characteristic testing of MEMS micro-devices was built based on a PZT transducer as the shock excitation source. A high voltage power source for the PZT transducer, which can provide large transient current, was developed for impact generation. Experiments for testing micro piezoelectric cantilevers were accomplished with the base excitation method. The impact response, i.e. electric charge signal generated by the micro piezoelectric cantilever, was acquired. By performing spectral analysis and comparison of the result with another cantilever having different resonance frequencies, the resonance frequency of the tested microstructure was determined. For comparison, simulation of the piezoelectric cantilever with a finite element analysis (FEA) method was carried out. Because the theory analysis is in good agreement with the experiment results, it can be used to estimate the actual resonance frequency of the tested microstructure. The base excitation method was also applied in the dynamic testing of microstructures under a high-g force environment. By the exclusion of the resonance peaks of PZT transducer and noise frequencies, the resonance frequency of the tested microstructure was determined. The applicability and the limitation of the method were briefly discussed.

This paper proposes an automatic three-dimensional (3D) surface contouring approach for accurate sphericity evaluation of micro tip balls of coordinate measuring probes using optical measurement and surface reconstruction. In the proposed approach, 3D volumetric data of the tip were constructed from cross-section contours using a 3D mapping algorithm. In addition, a volumetric intersection algorithm was derived from the optical perspective projection principle to remove artefact surface profiles from the volumetric data. A sphericity evaluation method involving minimum zone optimization was also developed to determine the sphericity of the inspected micro tip ball. The developed method is capable of measuring micro spherical balls having a diameter ranging from a few tenths of a micrometre up to several millimetres. An industrial case study was employed to verify the feasibility of the approach. The measurement results demonstrated that the proposed approach could achieve 3D surface reconstruction and evaluate sphericity of micro balls with maximum measurement errors of ±0.5 µm.

Multicycle synchronous digital phase measurement is proposed in this paper to further improve the phase measurement in phase-shift laser range finding. In the method, heterodyne processing is employed to convert the phase measurement of a high frequency signal into that of a low frequency signal, and by keeping phase measurement independent of the signal frequency to be measured and the gate signal synchronous with the measurement signal during multicycle phase measurement, errors caused by the frequency drift of a local oscillator during conventional auto-digital phase measurement are totally eliminated, and the time required to complete range measurement is shortened. Experimental results show that an uncertainty better than ±1.5 mm can be achieved at a data rate up to 20 Hz (t = 0.05 s) for a laser range finder using the method proposed with f_e = 10.000 MHz.

Mechanical principles of fibre-optic disc accelerometers (FODA) different from those assumed in previous calculation methods are presented. An FODA with a high sensitivity of 82 rad/g and a resonance frequency of 360 Hz is designed and tested. In this system, the minimum measurable demodulation phase of the phase-generated carrier (PGC) is 10⁻⁵ rad, and the minimum acceleration reaches 120 ng theoretically. This kind of FODA, with its high responsivity, all-optic-fibre configuration, small size, light weight and stiff shell housing, ensures effective performance in practice.

A large-scale laser plane calibration system is developed. This plane is constructed by a 35 m long horizontal granite guide rail and a 1.5 m long vertical metal guide rail. Two dual-frequency interferometers are used to measure the coordinates of a target moving on the plane. One of them can measure the horizontal displacement while eliminating the Abbe errors caused by the straightness of the granite guide rail. Another measures the sum of horizontal displacement and vertical displacement. This laser plane can be used as a lab standard to calibrate portable coordinate measuring machines by measuring the target on the plane. Calibration tests for a laser tracker are given.

An optical structured light method and an opto-electronic system for automatic noncontact distant measurements of wear and defect detection for a contact wire electro-supply network are presented. The industrial prototype of the system can extract the main technological wire parameters: the remaining height with the rms error down to 0.15 mm and the wire cross-section area with a rms error of 1.5 mm². This information is sufficient for confident decision making as to safe operation of the contact wire electro-supply network. This method could be applied for automatic wire wear measurement and defect detection for trams, trolleybuses and other electro-supply vehicles.

Ensuring the safety and high operation reliability of nuclear reactors takes 100% inspection of geometrical parameters of fuel assemblies, which include the grid spacers performed as a cellular structure with fuel elements. The required grid spacer geometry of assembly in the transverse and longitudinal cross sections is extremely important for maintaining the necessary heat regime. A universal method for 3D grid spacer inspection using a diffractive optical element (DOE), which generates as the structural illumination a multiple-ring pattern on the inner surface of a grid spacer cell, is investigated. Using some DOEs one can inspect the nomenclature of all produced grids. A special objective has been developed for forming the inner surface cell image. The problems of diffractive elements synthesis, projecting optics calculation, adjusting methods as well as calibration of the experimental measuring system are considered. The algorithms for image processing for different constructive elements of grids (cell, channel hole, outer grid spacer rim) and the experimental results are presented.