High resolution heterodyne interferometer based on time-to-digital converter

A new heterodyne interferometer is presented, which adopts time-to-digital converter (TDC) measuring the time intervals of zero crossings of heterodyne signal for phase demodulation. Thanks to the 0.1 ns time resolution of TDC and linear phase demodulation, it can achieve high resolution and avoids nonlinear measuring distortion in other indirect high precise phase demodulation methods, such as pulse width modulation (PWM) and in-phase∕quadrature (I∕Q) method.     

Validation of a single fibre-fed heterodyne laser interferometer with nanometre uncertainty

In this paper the validation of a fiber-fed heterodyne laser interferometer with nanometre uncertainty is presented. The achievable displacement measurement uncertainty is investigated for different polarisation maintaining fibres used in these interferometers. Measurement results are shown for both a range of m as well as a range of 300 mm. It is shown that a (selected) PM-fibre with an extinction ratio of 1:1650 and the use of an external reference allows realising a fibre-fed laser interferometer able to measure displacements with the same uncertainty as a laser interferometer system without fibre. Tests were performed with fibres ranging in length up to 50 m.     

An unmodulated bi-directional fringe-counting interferometer system for measuring displacement

A bi-directional fringe-counting Michelson interferometer is described that is used in conjunction with a frequency-stabilised laser for precise length measurement. The two counting signals, in phase quadrature and sinusoidally related to path difference, are produced by a novel system that does not employ any form of modulation. Under optimum conditions, the instrument is capable of measuring displacement to a precision of 0.1 μm and the correct fringe-count is maintained even with a signal attenuation corresponding to a 99% loss of intensity in one arm of the interferometer. This performance can be further improved by the application of an automatic gain control system. The interferometer is simple in concept, cheap to produce and easy to set up and align.     

Film thickness measurement by improved Michelson's interferometer

为了测量未知折射率或不透明薄膜的厚度,借助力传感器对传统迈克尔逊干涉仪加以改进,并运用等倾干涉的原理结合抵消法设计了测量装置.薄膜被等厚的空气层所代替,通过间接测量,避开了机械螺旋空程差造成的影响,使用力传感器有效减小了挤压形变引起的误差.该装置测量范围为0.3 μm～1.5 mm,分辨力为0.3 μm.实测数据表明,该装置具有良好的重复性和准确性.     

An interferometer for measuring surveyor's pillars in the open air

Electronic distance meters are performance tested on a 650 m long baseline at the National Measurement Laboratory, Sydney, Australia. The distances between the pillars which make up the baseline must be measured in a way which is traceable to the international definition of the metre. A laser interferometer has been developed to measure one of the intervals in a very accurate manner. It has some novel features to allow the use of a simple carriage-way to transport the reflector and has demonstrated a measurement accuracy of 0.2 ppm over a distance of 80 m in the open air.     

Measurement of large internal diameters with a compact apparatus based on dual-wavelength heterodyne interferometer

This paper presents a new method for measuring large internal diameters of 3∼20 m with submillimeter resolution. The method is based on a novel dual-wavelength heterodyne interferometer for absolute distance measurement and a new positioning method for aligning the laser beams with the diameter of the bore to be measured. The compact apparatus and convenience of operation in situ are the distinguishing features of this method. Preliminary experimental results of the prototype of the apparatus proved the feasibility of this method.     

Influence of glass substrate thickness in laser scribing of glass

The thickness of the glass substrate used in liquid crystal displays continues to be decreased from its original thickness of 1.1 mm for the purpose reducing size and weight. The aim of this study was to clarify the influence of the glass substrate thickness during laser scribing with crack propagation caused by laser heating followed by quick quenching. The laser scribe conditions for soda-lime glass substrates with thickness equal to or less than 1.1 mm were obtained in laser irradiation experiments. Two-dimensional thermal elasticity analysis was conducted with a finite element method based on the scribable conditions obtained in the experiment. The laser scribable conditions can then be estimated by the upper limit of the maximum surface temperature, T_max, and the lower limit of the maximum tensile stress, σ_tmax, in the cooling area, regardless of the glass substrate thickness. There is a substrate thickness with which the maximum tensile stress σ_tmax becomes the largest under each scribe condition. The substrate thickness with which σ_tmax becomes the largest is obtained at a faster scribe velocity for thinner glass substrate and at slower scribe velocity for thicker glass substrate. Owing to these relations, the crack depth also has almost the same tendency as σ_tmax.     

Two color multichannel heterodyne interferometer set up for high spatial resolution electron density profile measurements in TJ-II

A high spatial resolution two color [CO(2), λ=10.6?μm/Nd:YAG (Nd:YAG denotes neodymium-doped yttrium aluminum garnet), and λ=1.064?μm] expanded-beam multichannel heterodyne interferometer has been installed on the TJ-II stellarator. Careful design of the optical system has allowed complete control on the evolution of both Gaussian beams along the interferometer, as well as the evaluation and optimization of the spatial resolution to be expected in the measurements. Five CO(2) (measurement) channels and three Nd:YAG (vibration compensation) channels have been used to illuminate the plasma with a probe beam of 100 mm size. An optimum interpolation method has been applied to recover both interferometric phasefronts prior to mechanical vibration subtraction. The first results of the installed diagnostic are presented in this paper.     

A facility for measuring the thickness of thin metal films

A facility is described for measuring the thickness of a thin metal film. A measurement method is proposed that is based on the dependence of the phase velocity of harmonic antisymmetric Lamb waves that propagate along the film on the film thickness. A continuous method for excitation of acoustic waves has been applied to velocity measurements. It makes it possible to eliminate the effect of dispersion of the Lamb-wave velocity on the measurement accuracy.     

Determination of the energy of a relativistic electron beam by measuring the thickness of the colored layer in glass

A method for determining the energy of relativistic electrons, which was used in the investigation of electromagnetic fields in plasma and dielectric structures, is described. The electron energy was determined by the extrapolated track of electrons in glass, which was estimated by the thickness of the colored (darkened) layer formed by electrons. The density distribution of the colored layer along the direction of electron motion makes it possible to record the width of the beam energy spectrum and the beam position relative to the axis of the transit channel. A stack of glass plates on which the beam is incident can be installed in the transit channel of the dielectric structure or in plasma. Each plate in the stack is placed in parallel to the beam axis. After irradiation of the plates with relativistic electrons, the colored layer depth and the density distribution are determined. Examples of determining the electron energy of a pulsed relativistic electron beam are presented. The method is insensitive to electromagnetic noise, is inexpensive, simple, and easy to use.     

Modulated heterodyne light scattering set-up for measuring long relaxation time at small and wide angle

We present a simple, compact, and versatile experimental setup working in the heterodyne detection mode with modulation of the reference beam. The system is implemented with a collection optics based on a unimodal optical fiber coupler. This choice allows the heterodyne to be used in a wide range of scattering angles, even for very small ones, without losing the optical beating. The apparatus can be successfully used to study translational diffusive dynamics of dispersed particles at scattering angles smaller than 5° and it is suitable for exploring slow relaxation processes in sub-Hertz frequency domain, for example, in glass-forming systems. It is also possible to measure the electrophoretic mobility by applying an electric field into a charged particles solution.     

Improved techniques for measuring the indentation and thickness of articular cartilage

A review of the techniques previously employed in the indentation and measurement of the thickness of articular cartilage has led to new and improved techniques for performing both measurements. By utilizing high-speed, microcomputer-controlled data logging techniques, simultaneous monitoring of signals from a dynamic load cell and a displacement transducer could be made throughout an indentation test. The position of the indenter as it touched the articular surface could thus be determined automatically by identifying the moment at which a positive change in the load signal occurred. Less accurate and more time consuming techniques previously required for determining the position of the cartilage surface were hence avoided. The apparatus also included a critically damped dashpot which prevented any transient loads being applied to the cartilage. Depths of indentation could be measured to an accuracy of 0.005 mm with a measurement repeatability of 2.14 per cent. By replacing the indenter with a sharp needle, the apparatus was also capable of measuring the undeformed thickness of cartilage. An accuracy of +/- 0.012 mm could be achieved with a measurement repeatability of 1.2 per cent. The apparatus is particularly suited to survey work where large numbers of indentation tests are to be performed.     

An alternative method for measuring small displacements with differential phase difference of dual-prism and heterodyne interferometry

This study proposes an optical method for measuring small displacements. In this method, two semispherical prisms are used as test apparatuses. Because testing lights inside the prisms are at polarization angles, the phase difference can be differentially magnified twice and the measurement resolution can be greatly increased. Furthermore, using common-path heterodyne interferometery ensures that this method is simple to implement, high accurate, and high stability against the vibration of the surrounding environment. The capability of this method was demonstrated with a sensitivity of 42.92°/mm and a resolution of 23.29 nm.     

An interference technique for measuring the thickness of semi-thin and thick sections

An interference method is described for measuring section thickness in the range 0·3–45 μm. An incident illumination objective incorporating a beam splitter and adjustable reference mirror is used to generate interference fringes by reflection from the upper surfaces of sections on glass slides. Sections do not require a reflective coating. The lateral displacement of the zero-order fringe generated using white light is measured in terms of sodium light fringes and photographic enlargement of the fringes allows measurement to ± 30 nm. The method is simple in operation and allows rapid assessment of any local distortions over the entire section area.     

An eddy-current gauge for measuring the wall thickness of light-alloy drill pipes

The operating principle and design of an eddy-current transducer intended for in-service measurement of the wall thickness of light-alloy drill pipes are described. The block diagram and algorithm of conversion are provided for measurement-data signals from the eddy-current thickness gauge. The main technical specs are listed for a thickness gauge prototype.     

A 10 mm measuring machine based on a compensated laser interferometer

A single-axis measuring microscope has been constructed for the calibration of stage micrometers, micrometer microscopes and similar devices which require uncertainties down to 0.1 μm. The instrument is built from modules so that the interferometer measuring unit can be used in a variety of calibration tasks. A single mode optical fibre can be used to couple the laser source to the interferometer     

超声波测厚系统的研究

深孔加工是一种封闭式或半封闭式状态下的加工,其加工过程很不稳定,深孔加工刀具的走偏现象直接影响被加工孔的直线度,造成被加工工件报废,所以在深孔加工过程中的实时检测就显得尤其重要.根据深孔加工系统的特点,将超声波测厚原理用于单管内排屑喷吸钻深孔加工在线监测中,通过检测被加工工件壁厚来判断刀具是否走偏,结果表明,该测试装置较好地解决了深孔钻削加工刀具走偏的监测问题.     

Integration of a laser interferometer and a CMM into a measurement system for measuring internal dimensions

In order to improve the existing comparative procedure for calibrating internal dimensions, we have developed a new measurement set-up for traceable absolute measurements. It consists of a co-ordinate measuring machine (CMM) and a laser interferometer (LI). The LI serves as a traceable measurement system, while the CMM is only used as a guiding system for the measuring probe. Extended research focused on defining probe parameters such as diameter, bending and indentation, as well as probing head repeatability and other error sources. The final goal of the research was to determine uncertainty of measurement under existing laboratory conditions. The main outcomes of the research and final uncertainty of measurement are presented in this article.