In this paper we describe the status of our research on the use of diode lasers for absolute distance interferometry, and we discuss the major sources of uncertainty that limit the accuracy of this technique for distance measurement. We have primarily employed a 670 nm external cavity diode laser as the tunable source for our interferometer, but currently, we are developing a system based on an 850 nm distributed Bragg reflector laser. These two laser have very different strengths and weaknesses; the primary sources of uncertainty in length measurement depend on which laser is employed.

Grazing incidence interferometry using diffractive elements is a modern laser-optical high precision measuring technique suitable for technical surfaces to measure from deviations of cylinders. Advantages in comparison to tactile measuring techniques consist mainly in a large number of measuring points sampled at the entire cylinder jacket area with high radial resolution in a very short time so that an improved reliability of the measurement, which represents the real surface of the workpiece under test, is achieved. This contribution gives a short introduction to the principle of interferometric cylinder form testing. An own set-up is presented as well as a stationary measuring system, working both according to the transmission method. As a modification of this, a mobile sensor, which is able to measure bores accessible only on one side, is introduced. The potential of grazing incidence interferometry is demonstrated by means of comparative measurements with conventional tactile measuring methods.

Gauge blocks are known to be the most important and commonly used material standards in maintaining traceability in dimensional metrology. They are regularly used in international comparisons of interferometric measurements to assess the accuracy of the length SI-unit, reproduced in different countries, as with the help of interferometric comparators the length of the block can be directly determined in terms of vacuiini wavelengths of standard radiations [1]. In many countries the primary level comparators are similar to the big KOsters interferometer [2-3], where a plane light wave of big aperture is propagating in vacuum and after reflection from a plane mirror forms a standing wave, with a precisely known separation between the points of equal intensity (fringes). This standing wave is then used to find the length of a gauge block in terms of the vacuum wavelength, which is calculated as the ratio of the speed of light (explicitly fixed in the present definition of the Metre) and the laser frequency, known from the absolute frequency measurements performed against the primary Cs standard. The procedure of length measurement in this instrument requires a flat reference plate to be wrung to one of the faces of the gauge block. For short gauge blocks, of a few mm nominal lengths, the largest uncertainties in the accuracy budget of the interferometric measurement [4] arises due to the phase change correction [2] (±12 nm at 95% confidence level [4]) and due to the variability of the wringing film thickness (±12 nm at 95% confidence level [4]). In some papers [3,5], for selected blocks with smaller deviations in flatness, the variability of the wringing film thickness is reported to be about nm (at 95% confidence level). In this paper, we describe a new approach in the interferometric length measurements that is based on the technique of the reproducible wringing [6-9]. It gives the opportunity to measure the physical length of the material artifact without the excessive wringing film thickness and results in the accuracy of the phase change measurements at the optical reflection from surface of the material standard of better than I nm.

The purpose of this paper is to present a general method to estimate the intrinsic performances of some laser range finders based on flight time measurement. Classically this flight time can be measured directly, or after a conversion into a phase shift, or into a beat frequency. We prose here a criterion based on signal processing notions, as matched filtering to get the best detection, and ambiguity function to estimate the quality of the detection. The concept of characteristic length is introduced and applied to the different kind of laser range finders, which suggest a new possibility for flight time measurement.

This work discusses the working principle and mechanical details of a new scanning transducer for angle measurement between IR modulated emitters placed in known positions. The system can be used for position estimation of AGVs inside structured environments. Position is computed by triangulation. The advantage of the proposed transducer is that, having approximately the same accuracy of the commonly widespread laser system, it makes us of active targets, which allow a further degree of freedom: height for target installation. In other words, coplanarity between targets and plane of scanning is no longer required. Consequently, target visibility may be achieved even in the case of bulky machinery placed inside the factory environment. Repeatability error in angle estimation is +/- 47 arcseconds, which means that positional accuracy in a square 10 m room is +/- 2 mm.

Material testing provides experimentally determined parameters which characterize the sample's properties under mechanical or thermal loading conditions. As long as no relevant gradients of the properties occur, the classical strain gauge method can be successfully applied.

Optical monitoring (OM) during film production is considered for thermal vacuum and spin coating processes. During spin coating, OM has allowed identification of several phases during film formation, and characterization of the temporal dynamics may improve control and reproducibility in film production. For films grown under high vacuum, optical monitoring allows continuous inspection of the interference signal, with typical determination of optical thicknesses in multiples of quarterwaves. Long trial-and-error procedures are avoided, even under presence of density fluctuations during deposition. Instrumentation and metrologic aspects are presented. Examples are given of liquid film deposition for silicate sol-gel films and silicone oils, as well as of thermal evaporation of ZnSe and ZnS films. In these, we also performed an intercomparative analysis with the post- process, spectrophotometric envelope method. Optical interferometry monitoring is non-destructive, can be integrated to film manufacturing processes, allows precise metrological procedures, and can be applied to the real-time and in situ characterization of a wide variety of non- opaque, liquid or solid, films.

A touch probe is used on a 3-axis vertical machine center to check against a hole plate, calibrated on a coordinate measuring machine (CMM). By comparing the results obtained from the machine tool and CMM, the main machine tool error components are measured, attesting the machine accuracy. The error values can b used also t update the error compensation table at the CNC, enhancing the machine accuracy. The method is easy to us, has a lower cost than classical test techniques, and preliminary results have shown that its uncertainty is comparable to well established techniques. In this paper the method is compared with the laser interferometric system, regarding reliability, cost and time efficiency.

This paper will guide the first-time user toward proper selection and use of IR detectors for applications in industrial inspection, process control, and laser measurements.

Lasermikes (LMS) measure linear displacement indirectly - through angle and time measuring, assuming constant scan velocity. In order to meet present accuracy requirements the direct method of angular position measurements and the optimization of the system is proposed. The method is based on angular laser microinterferometer measuring directly the deflector scan angle. The obtained resolution was 0.02 inch. The analytical considerations of detector signal led to the creation of 'hump phenomenon' - formed by the light reflected from the object surface and having the decisive influence on the form of detector signal. It is proved that the detector error can be significantly reduced by optimizing the detector system according to the object size and reflectivity. The paper contains the description of the angular laser microinterferometer and its metrological properties and the analysis of detector output signal when scanning the cylindrical object with focused laser beam. It was proved that by introduction of the direct angle measuring method and optimization of the system, the required accuracy of lasermikes can be achieved.

A new dual frequency laser interferometric path measuring system is introduced that has been developed especially for the precision rapid-positioning systems of microlithographic large-scale instruments and for ultra-precision technology. The modulation frequency of 640 MHz, generated by a highly- stabilized He-Ne-laser allows, in combination with a novel HF signal processing method, measuring velocities up to 3.2 m/s without 'losing' even the least increment. It is a further metrological merit that the least increment is not generated by an additional LF interpolation - as in common - but arises from the parallel processing in the HF part. Practical examples for civil engineering, production integrated measurement, and quality control will be given.

Electronic Speckle Pattern Correlation Interferometry (ESPI) is used as a tool for NDI, in many aspects complementary to x-ray or ultrasonic techniques. Many technical structures are to be inspected from the inside but are not accessible to conventional ESPI. Endoscopes as known from visual inspections lend themselves to circumvent this limitation. The endoscope is used as an 'extended lens' to transfer the object wave to the interferometer. We us the ring shaped illuminating fiber bundle of a rigid endoscope for beam delivery. For observation and object wave transfer the relay optics of the endoscopes is used which results in a very good image quality. In laboratory environment stability and beam quality of this set-up is adequate for NDI-applications in spite of the multi-mode multi-fiber character of the illuminating fiber bundle, since the bundle is mechanically rigid.

This paper presents a new kind of double illumination interferometer used for radial in-plane displacement measurement through electronic speckle pattern interferometry (ESPI). Some characteristics and implementation details are discussed. This new interferometer is used for residual stresses measurement combining, in a very efficient way, the blind hole method and the in-plane radial displacement measurement by ESPI. Algorithms and implementation characteristics are also discussed. A portable device was built to measure residual stress outside the optical bench. Early results show a measurement performance comparable to the conventional blind hole method using strain gages. Measurement time is almost one order less than the strain gage based measurement system.

ESPI is classically used in high resolution measurements of deformation, but ESPI can also be sued for contouring of surface even with discontinuities. Furthermore, measurements of both shape and deformation had been carried out. It has been shown that performing both measurements is necessary to obtain the actual strain information at the specimen topography, and the development of such techniques was presented as an alternative to other strain measurement methods, among who wire resistance strain gauges is the most popular one. But, despite its reliability and popularity, the strain gauges technique has some disadvantages. Its set- up is very time-consuming: in order to assure tight contact between gauge and measured surface, one has to take care about the specimen surface cleanliness and roughness and the gluing step takes hours; mounting the electric circuit also request for time and work due to the small voltage signs, demanding high sensible signal amplifiers and bridge-circuit units able to perform compensation of temperature variation and protection from noise. Beside s that once the given strain information result from the integration over the whole area covered by the gauges, this technique gives no lateral resolution.

Image plane digital holography is used to evaluate the 3D vector components and object contour of a dynamically moving object. Pulses from a Q-switched ruby laser are used to record image plane holograms on the faceplate of a CCD camera, to be later digitally reconstructed. Three different illumination directions are used to get displacement information along three different sensitivity vectors. The latter are combined into a 3D resultant displacement vector for every object point. To compete the full 3D analysis the object contour is measured with the two-wavelength method. Data for contour and 3D-displacement are combined and displayed.

The inclusion of pulsed lasers in video speckle interferometry has relaxed the limitations of stability and extended the range of engineering problems which can be solved with this technique. If an adequate procedure is used to synchronize the firing of the laser pulses with the state of vibration of the object, out-of-plane and in-plane interferometers can be used to measure fast non-periodic transient displacement fields. As only one phase distribution is available from a transient fringe pattern, its evaluation is usually carried out using the Fourier transform method through the introduction of carrier fringes between both laser pulses. This paper discusses some recent developments that have been implemented in this field and also presents experimental results obtained with different video speckle interferometry systems.

A new algorithm is described that uses only two mutually phase-shifted interferograms per deformation state and a mean intensity in order to retrieve the phase signal modulo 2 (pi) due to displacement. The algorithm was designed for spatial phase-stepping ESPI where the initial phase in the interference term is the phase of speckle that varies randomly over the imagine sensor. An analysis of phase measurement error is presented. System error sources considered here are imperfect phase stepping, variation of modulation depth and intensity noise. The algorithm was implemented into an out-of-plane sensitive interferometer for experimental verification. The paper discusses practical advantages, presents limitations and possible future enhancements of the system. Obtained experimental results prove that phase measurement uncertainties smaller than 2 (pi) /15 are feasible.

As any other kind of interferometry, electronic holography too s very sensitive for perturbation such as vibrations and air currents. Active phase stabilization has been known as an effective countermeasure for some time. We describe the implementation of such a closed loop which uses the camera as phase sensor, which allows us to stabilize our holography systems by a pure software addition.

A computer-generated diffractive optical element (DOE) is used in electronic speckle pattern interferometry (ESPI). This DOE is applied to calculate the interference phase corresponding to object deformation from a single TV frame. The system is utilized for static and transient deformation measurement with CW and pulse Nd:YAG lasers, respectively. The DOE is a modified phase computer generated hologram or cross grating. For transient deformation measurements the DOE does not need to be translated in order to introduce the phase change between diffracted fields. Thus, spatial phase- stepping becomes feasible and high-speed frame acquisitions do not limit real-time phase measurements. Experimental results for spatial phase-stepping with and without moving the DOE are given.

Optical triangulation, as a non-contact non-destructive method, extensively proved its usefulness on the topographic and dimensional inspection of objects and surfaces of use in the industrial world. In this paper we will present new advances on the development and applications of the microtopographers developed by the author at the Physics Department of the Universidade do Minho.

A commercial scanning force microscope (SFM) has been equipped with an additional 3D position measurement system consisting of three miniature laser interferometers. This modification serves to further improve its metrological performance and calibration. This SFM is applied to topographical measurements including several types of calibration. In order to avoid the influence of Abbe errors two new interferometers have been implemented in the SFM. From this results a reduction of the measurement uncertainty. Furthermore, we report on a combination of the SFM including incorporated laser interferometers with a sophisticated detection system of another commercial scanning probe microscope. This enables to analyze further interactions between probe and specimen.

A laser-interferometric miniature measuring system designed for precision measurements in the fields of micro-, nano- and macro technology is being presented. In measuring ranges of >= 2 m, a resolution of <EQ 1 nm and an accuracy of only a few nanometers can be achieved. On the basis of various practical applications of the 2D- and 3D-nano- measuring and positioning techniques, the particular advantages offered by the optical fiber-coupled laser- interferometric measuring system are explained.