To control processes capable of accuracy and surface finish requires surface measuring equipment of a very high order of capability and versatility. Metrology has also required a similar change in discipline to include more physical considerations than was considered necessary only a few years ago. In what follows some of the existing trends are reviewed.

Methods of non-electromagnetic laser beam scanning are discussed with respect to scanning angle, frequency, aperture, resolution, optical efficiency and manufacturing methods.

In this paper we discuss three questions relating to the use of reference data sets and reference results in black box tests for validating assessment software: (1) how to generate data and results, (2) how to represent solutions in a stable way and (3) how to compare test results and reference results. We describe a general method for generating data and results which goes some way to addressing all three problems and illustrate the concepts introduced for least squares form assessment and theodolite triangulation.

The image quality degradation due to atmospheric turbulence is one of the main limitations for imaging, laser propagation, communication, and metrology in the atmosphere. Adaptive optics is a technology to overcome these problems by real-time phase compensation. the main components exist for systems such as wavefront correctors, wavefront sensors, and dedicated computers, and have been successfully tested. This article describes the principles of adaptive optics and demonstrates the potential of adaptive optics for applications in astronomical imaging, including some first results. The image quality that can be expected from adaptive optics and requirements for its application are discussed.

The NPL provides a measurement service for the multistation field baselines which are used by the surveying profession to calibrate electronic distance meters. This activity employs the Mekometer ME5000, a precision laser distance meter whose predecessor was originally developed at the laboratory. To confirm traceability, the Mekometer can be compared directly with a fringe-counting laser interferometer by mounting the retroreflectors for both instruments on a moving carriage, but only up to 50 m. However, the range can be increased greatly by multiply reflecting the Mekometer laser beam between two large plane mirrors, one of which is mounted on the moving carriage. A change in the mirror separation as measured by the interferometer, when multiplied by the number of passes of the Mekometer beam, should agree with the change in the Mekometer reading. By this means, the claimed accuracy of 0.2 mm has been confirmed up to 550 m. The corrections needed for beam obliquity have a comparable order of magnitude.

Recent advances in semiconductor laser technology, which have led to compact sources potentially suitable for lidar, are described. Quantum well technology has enabled InGaAs laser arrays to provide powers of 800 mW in the 900 - 1000 nm wavelength region while InGaAsP lasers provide peak powers of 1.4 W at the eye safe wavelength of 1.55 micrometers . A distributed feedback structure has been used to simultaneously produce a mean power of 100 mW and a linewidth of 800 kHz which may be used for coherent lidar (e.g., FM cw).

In the paper a new angular scan triangulation range scanner is described using an integrated array of LED chips and a lateral-effect position-sensing detector. A range map is obtained by means of fast electronic scanning of the chips of an integrated LED array. One LED of the array operates at a time and a certain on-off switching sequence is applied. In the paper the operation principle of the scanner is presented and a design of the sensor prototype using a linear array of 32 LEDs is reported. Experimental tests for evaluation of the sensor performance are described, including range accuracy, precision, time of range image acquisition, and geometrical properties of the sensitive volume of the sensor. Range measurement tests for targets located at different angles in relation to the sensor and profile measurements of cylindrical objects are also reported.

Cooled adaptive bimorph copper and molybdenum mirrors are suggested for large-scale optical aberration compensation in laser systems with power up to 15 kW. Characteristics of developed and produced cooled bimorph mirrors are investigated and comparison of experimental and calculative results are carried out. In the last part perspective adaptive bimorph mirror constructions are suggested and discussed.

For quality control, volume determination, process monitoring and other tasks in industry, the application of 3-D measurement techniques is required. Out of the available 3-D methods, the optical radar shows special advantages. In this context, a system based on the method of optical radar as well as first results is described in more detail. The new system provides data for 3-D scene analysis with the spatial coordinates of a surface to be determined in a pre- defined volume. A complete 3-D picture with 500 X 500 pixels is recorded and evaluated within less than 2 seconds.

A new instrument is described which enables spatial position measurements to be made to single targets or to targets disposed in a known spatial array. In the measurement process the geometrical shape of projected laser beams is used to determine either target direction or position. One application area for this portable instrument is introduced, namely for the in-situ spatial calibration of robot end-effectors.

A family of high performance industrial laser scanners has been developed at Philips, based on a unique, reflective, field flattening system as an alterative for f-(Theta) scan lenses that are usually applied in laser scanners. This novel scan approach enables pure telecentric and flat field scanning of wide formats at very high resolution and speed. The attractive features of this particular scan concept are demonstrated by two different 2-D industrial inspection problems that have been solved at Philips during the last ten years.

Two examples of specific design philosophies for low-cost on-line inspection systems for textiles are described in this paper: The application of the moire-technique can heavily enhance the imaging of textile surfaces as a filter for the assessment of geometric variations of the textile `grating' with extremely simple algorithms for image analysis. Blinded for color shades triangulation sensors have been developed into powerful tools for fast profiling of textile surfaces. Curtailed for certain applications fiber optical modifications of the basic triangulation principle have been developed for aereal inspection.

Calibration standards for volumetric accuracies of CMM and machine tools are described. Automated measurement techniques using laser interferometers can speed up measurement time.

A non-contact shape measuring system using fiber optics and digital speckle pattern interferometry (DSPI) is described. Fringe patterns for obtaining the height distributions of the shape are generated by traversing one of the illumination beams. The system utilizes a 4-step phase stepping algorithm to perform the data reduction. A semi-automatic procedure for calibrating the piezoelectric phase shifting device is reported. The equations for calculating the surface height are stated and typical results for two specimens are shown. Advantages and limitations of the technique and the optical system used are discussed.

Long term research on pulsed time-of-flight laser distance measurement has opened new dimensions in measurement applications, from large scale assembly in shipbuilding to precast concrete element production, leading to improved quality control and more efficient manufacturing. The ACMAN 3-D coordinate meters measure the coordinate values of a point in terms of radial distance and two angles directly from natural surfaces. The accuracy of coordinate values is 1 mm (1-sigma) in the measurement range of 3 - 30 m. The functions of the automatic ACMAN 200 include pointing with a red beam, automatic searching and measuring of marked target points and shape measurement by scanning. Coaxial optics of measuring, pointing and aiming provide the optimal measurement geometry. ACMAN 3-D coordinate meters are integrated into the ACMAN 1000 and ACMAN 2000 series dimension control systems.

Roke Manor is developing a family of instruments for the automatic measurement of radius of curvature of any polished surface by non-contact means. These instruments can be of use in the optical workshop, and other places where in-situ measurements are required to be made. Simultaneous measurements of external and internal surfaces can be made and information supplied on decentration and tilt. The family of instruments removes the requirement for accurate test surfaces as required by interferometry, and the long working distance objectives of auto-collimators, while maintaining accuracy. The measurements are accomplished by non- contact means and can be made by personnel unskilled in conventional methods, such as interpreting interference fringes.

A closed-loop positioning system is described which is capable of sub-nanometer precision over displacements of up to 100 micrometers. The technique utilizes piezo-electric or electrostrictive translators in conjunction with capacitance displacement sensors. It has been applied in optical interferometry for path length control to picometer precision, and in X-Y stages developed for scanning probe microscopy.

A new method for the measurement of linewidths on integrated circuit photomasks using an optical microscope is described allowing the accurate measurement of features which are not fully resolved, even when the instrument is not perfectly focused and there is considerable spherical aberration in the optical imaging system. This paper demonstrates how an optical microscope which produces scaled image intensity profiles can be calibrated to exploit a new measurement algorithm.

A factor-of-ten over classical diffraction limit enhancement was achieved with a Computer- aided Phase Microscope `Airyscan.' It also permits dynamic processes registration at any selected point of the image. The theoretical backgrounds of the new approach to the problem of super-resolution are discussed. `Airyscan' may be useful in a wide range of scientific and industrial applications. Special attention is paid to biophysics and medicine.

A recent development of the slope integration method in the form of a 2-D laser profilometer system has been applied to measure the figure of reflecting mirrors for x-ray imaging applications. The mirror surfaces were either spherical or paraboloid in form and in some cases could be bent into the required form. The lengths of the surfaces examined varied from 35 mm to 500 mm with sagittas of up to 60 micrometers . At present surfaces with a maximum scan length of 300 mm in 1-D can be measured with an estimated systematic uncertainty of +/- 6 nm for flatness. Over the full angular measurement range of 5 arc minutes the accuracy is slightly reduced. In 2-D, flatness over an area of 100 mm X 100 mm can be measured repeatably with a precision of +/- 2 nm. The angular range of the method has been increased to 1 degree(s) in 1-D to cater to surfaces with radii of about 20 m.

New software algorithms are presented which extend the measurement capabilities of phase measurement microscopes without employing exotic hardware. Efficient methods for averaging data and compensating for common electrical artifacts produce measurements of 0.2 Angstroms rms instrument noise, regardless of the orientation of the interference pattern. A method for calculating the fringe order for each phase data point allows measurement of discontinuous surfaces without the usual phase unwrapping problems.

An absolute interferometric dilatometer is described. It has been designed to measure the linear thermal expansion coefficient of gauge blocks up to 125 mm long. The instrument uses an electrically heated oven to control the temperature of up to 10 gauges at temperatures between about 20 degree(s)C and 37 degree(s)C. A Fizeau interferometer is used to measure the length of the gauges in terms of the wavelengths of frequency stabilized He-Ne lasers using the method of exact fractions. Preliminary results indicate that the target uncertainty of +/- 1 X 10^-7 K^-1 for the thermal expansion coefficient can be achieved for 100 mm steel gauge blocks.

Micromechanics is placing new demands on surface metrology equipment due to the fragility and small size of the mechanical components being fabricated. For research and development purposes both static measurement of component dimensions and thickness and dynamic measurements of deflection and vibrational amplitude are essential. This paper describes a new laser based non-contacting surface measurement system which is finding increasing application for these tasks. The system employs the dynamic focusing principle and has a measurement range of 1000 micrometers and a vertical resolution of 6 nm. The lateral resolution of the system is 1 micrometers and measurements may be made at up to 10 KHz. A built in observation window allows simultaneous measurement and observation of the measurement spot and surrounding region.

A two-mirror multiple-beam interferometer is described for which frequency dispersion of inter-mirror space is compensated by equal in magnitude but opposite in sign dispersion of the mirrors themselves.

A new method of optical, non-contact profiling of rough surfaces is described that utilizes interferometric techniques as well as digital signal processing algorithms to produce fast, accurate, repeatable 3-D surface profile measurements. When combined with more traditional phase-shifting measurement techniques, this produces an instrument capable of profiling surfaces with rms roughness, Rq, ranging from 1 angstrom to 20 micrometers , and measurement of steps up to 100 micrometers . Sample data are discussed and a comparison with other surface profiling techniques is presented.

We are dealing with the description of an optoelectronic instrument which does not necessarily need in-focus images for dimensional measurements. Assuming the point spread function (PSF) as Gaussian, spherical particle diameters are deduced from the image contrast and the cross-section areas of the defocused images. Here, a cross-section area is defined by the number of pixels whose grey level is inferior to the mid-point intensity. The instrument makes use of two CCD cameras with the same angle of view. The source is a double pulsed multimode laser diode. One of the CCD cameras is exposed to two pulses and the activation of the other is delayed for only recording the object field illuminated by the last pulse. Then the two video signals are subtracted. This operation increases the signal/noise ratio (SNR). The contrast of one image being inversed, not only the amplitude of the particle velocity but also its sign, can be determined.