Scanning White Light Interferometer Research Articles

Self-calibration for microrefractive lens measurements

The self-calibration test known as the random ball test (RBT) is adapted and applied to instrument calibration for measurements of microrefractive lens figure error. The RBT exploits the symmetry properties of a microsphere, resulting in a low-uncertainty estimate of the instrument biases. One hundred surface patches on a 1-mm-diam steel sphere are imaged by commercial instruments then averaged together in software to determine the instrument bias for a 500-µm radius of curvature test piece. The results show biases on the order of a few hundred nanometers peak-to-valley for a scanning white light interferometer and a Twyman-Green interferometer.

Scanning white-light interferometer for measurement of the thickness of a transparent oil film on water

The thickness of a transparent layer of oil upon the surface of water is measured as the distance between the surface of oil film and the interface of the oil with the water. Two experimental results have demonstrated that the interface can reflect a white-light beam well enough to form an interferogram, even if the light is subjected to oil-film dispersion. When a beam of white light is incident vertically onto the oil-film surface, a scanning white-light interferometer in the Michelson configuration is employed to locate two serial reflections, surface reflection and interface reflection. The thickness of the transparent oil film on water is calculated based on the separation of these two interferograms. A limitation thickness, approximately 250 microm with 1.25 microm resolution, is achieved under the condition that there is 50 nW of optical power incident onto the oil-film surface with a wavelength centered at 1310 nm.

Spatial resolution enhancement of fiber-optic scanning white-light interferometer by use of a Vernier principle.

A Vernier principle is employed to improve the spatial resolution of a fiber-optic white-light interferometer to the accuracy of 0.2 microm. The Vernier principle is implemented by combination of interference fringes itself and a virtual fringe that is generated by means of software tracing the scanning mirror. Two rulers are read with respect to each other. This design is insensitive to intensity fluctuation of the interference fringe. The applications, submicrometer estimation for the quadrature-locking selection and the tolerance of the relative measurement, demonstrate its effectiveness.

新面感評価法の各種塗工紙への適用について

Coated paper is required to have excellent sheet appearance. And it is well known that sheet appearance is affected by gross profile. Evaluation of sheet appearance is generally determined by visual inspection. However the evaluation method is subjective and not quantitative, so that the evaluation of sheet appearance is too difficult. For purpose of quantitative evaluation of sheet appearance, a few methods have been reported.We reported that we developed a new evaluation method of sheet appearance of coated paper with using Scanning White-Light Interferometer (ZYGO New View system). And we found that the standard deviation of average of surface slope angles (ASSA) was strongly related to sheet appearance.That is, we can conclude that the more distribution of ASSA becomes uniform, the more sheet appearance becomes better.In this paper, we measured distribution of ultra fine surface profile of various commercial coated papers, and studied influence of the standard deviation of ASSA to sheet appearance.As a result, we found that the optimal threshold of ASSA at binarization changes with kinds of coated papers and optimal threshold is ±7 ° for A 2 coated paper or ±10 ° for A 3 coated paper. We also found that correlation with sheet appearance is the best, when it is not concerned with the kind of coated papers but the slope angle area ratio (SAAR) at binarization becomes 70%.

Relationship of the plasticity index to machining parameters

An analysis is made of roughness measurements made at two different sampling intervals with a scanning white-light interferometer on 17 plateau-honed cylinder liners. Plasticity indices are calculated for both sampling intervals according to two different methods. For both methods the values of plasticity index are found to be significantly different for the two sampling intervals, as expected, but there is no correlation between the two sets of measurements. One plasticity index is inferred to be about three times the other, in fair agreement with experiment. An error analysis is carried out which when applied shows that the proportional uncertainties in the two versions of the plasticity index are about the same. A factorial analysis suggests that to achieve a lower value of the plasticity index, the initial honing pressure should be reduced and plateau honing time should be increased.

Quasi-distributed white light fiber optic strain sensor

Development and characteristics of a quasi-distributed intrinsic fiber optic strain sensor based on white light interferometry is described. The research presented here describes the development of a new optical fiber sensor system for measurement of structural strains based on white light interferometry. Individual segments of single mode optical fibers are linked in series and a scanning white light interferometer provides for distributed sensing of strain signals from various locations in the structure. The system can be configured for automatic compensation of drift due to environmental effects, i.e. temperature. The experimental results demonstrate the linearity of the system and the capability for distributed sensing of strains.

Quasi-distributed fiber-optic strain sensor: principle and experiment.

Sensors capable of making distributed measurements allow for monitoring of the entire structure. Optical fiber sensors are especially attractive for this purpose, since they are geometrically versatile and can be readily integrated within various types of structure and material. Development and characteristics of a quasi-distributed intrinsic fiber-optic strain sensor based on white-light interferometry are described. The research presented here describes the development of a new optical fiber sensor system for measurement of structural strains based on double white-light interferometry. Individual segments of single-mode optical fibers forming a common-path interferometer are linked in series, and a scanning white-light interferometer provides for distributed sensing of strain signals from various locations in the structure. The system is configured for automatic compensation of drift due to environmental effects, i.e., temperature and vibration. Strain gauges were employed for comparison and verification of strain signals as measured by the new system. The experimental results demonstrate the linearity of the system and the capability for distributed sensing of strains.

Lateral scanning white-light interferometer

White-light vertical scanning interferometry is a well-established technique for retrieving the three-dimensional shapes of small objects, but it can measure only areas as big as the field of view of the instrument. For bigger fields a stitching algorithm must be applied, which often can be a source of errors. A technique in which the object is scanned laterally in front of an instrument with a tilted coherence plane is described. It permits measurements at higher speeds while measurement accuracy is retained and eliminates the need for stitching in one direction. Experimental confirmation is provided.

Influence of Ultra Fine Surface Profile to Sheet and Print Gloss of Coated Paper

Coated papers are required to have excellent sheet and print gloss. Surface roughness of coated paper is well known to correlate with these properties. However it is not clarified about the detailed concern between surface profile and these properties.So. we measured ultra fine surface profiles of coated papers with using Scanning White-Light Interferometer (ZYGO New View system) whose principle was based on the measurement of interference fringe variations, which was a technique for profilometry constructing an ultra fine three-dimensional profile accurately and rapidly without contacting the surface.In this study, we considered the influence of ultra fine surface profiles to sheet and print gloss of coated papers, and clarified about the concern between them with using this technique. Then we turned out the correlation between surface profile and gloss with the parameter that was a detail surface roughness.As a result, it was found that to consider surface profile of coated paper as a cluster of waves that had various frequencies, and to process complex surface profile in term of spatial frequencies and parameters was very useful. Especially, it was found that the ultra fine surface profile of specific waves with the spatial frequencies more than 30/mm or 40/mm had affected sheet gloss of coated paper greatly. Moreover, it was also found that print gloss was influenced by the waves with a larger range of spatial frequencies than the specific waves that influenced to the sheet gloss.

Modified 2D stylus profilometry and its application to frictional analyses in sheet metal forming operations

Frictional conditions at contact interfaces can have a large influence on the success of some sheet metal forming operations. Topographic surface characterisation is a useful tool for obtaining data necessary for some tribological analyses, and it is proposed that a standard two-dimensional (2D) profilometer can be modified to provide inexpensive three-dimensional (3D) data without any significant loss of performance. A scanning white light interferometer is used to verify this hypothesis, and the results show that while the new profilometry technique is less accurate at low contact areas, it is sufficiently accurate for some purposes. Surface maps are created and the results used to calculate the real contact areas, bearing area curves and hydrodynamic lift pressures for a drawing-quality steel.

Fractal characterisation of the anisotropy of rough surfaces

Existing techniques for measuring and characterising anisotropy are discussed. The advantages are suggested in treating anisotropic surfaces as self-affine fractals, characterised by two parameters, the fractal dimension and the topothesy. These parameters are conveniently determined experimentally by measuring the slope and intercept of a logarithmic plot of the structure function. A 3D version of the structure function is presented, any section for which is equivalent to an ensemble average of profile structure functions. The angular variation of topothesy and fractal dimension obtained from such sections describes the anisotropy of the parent surface. Also, a bifractal structure function, typical of surfaces with stratified textures, may be split into its component straight lines by fitting with a hyperbola. The intersection of the asymptotes then defines the so-called “corner frequency” between the two fractals. The 3D height measurements were made on a grit-blasted, a ground and a plateau-honed surface with a scanning white-light interferometer and a stylus instrument. On the isotropic grit-blasted surface, fractal parameters did not vary with direction. On the strongly anisotropic ground surface, the fractal dimension varied only parallel to the lay, as predicted, but the topothesy varied by some orders of magnitude. On the stratified plateau-honed surface, the only true bifractal, fractal parameters were found to be sensitive to the direction of honing scratches.

Ablation smoothness as a function of excimer laser delivery system

Objective: To quantitatively study and compare the ablation profiles of three kinds of excimer laser delivery systems to identify which technology provides the smoothest ablation profile.Setting: Three private practices, one in Canada and two in the United States.Methods: Excimer laser myopic ablations were performed on poly(methyl methacrylate) (PMMA) test blanks in 3.00 diopter increments using a 5 mm optical zone with three kinds of excimer laser delivery systems: (1) iris diaphragm without beamhomogenizing technology (ExciMed, Summit Technologies, Inc.); (2) iris diaphragm with beam homogenizer (20/20, VISX, Inc.); (3) galvanometric scanning (MiniExcimer, LaserSight, Inc.). We used a scanning white-light interferometer (NewView 100, Zygo Corp.) to study three measures of surface smoothness: peak to valley, root mean square average deviation height (RMS), and the arithmetic average deviation from the center line of the data.Results: Using RMS as a measure of surface smoothness in an optical system, the galvanometric scanning delivery system produced ablations approximately three times smoother than the iris diaphragm with beam homogenizer (P = .01), which in turn produced ablations about twice as smooth as the iris diaphragm without beam homogenizer (P = .03).Conclusions: Galvanometric scanning delivery systems provide a significantly smoother ablation profile than iris-diaphragm (variable aperture) systems.

Surface Profiling by Analysis of White-light Interferograms in the Spatial Frequency Domain

Abstract We describe a scanning white-light interferometer for high-precision surface structure analysis. Interferograms for each of the image points in the field of view of the instrument are generated simultaneously by scanning the object in a direction perpendicular to the object surface, while recording detector data in digital memory. These interferograms are then transformed into the spatial frequency domain and the surface height for each point is obtained by examination of the complex phase as a function of frequency. The final step is the creation of a complete three-dimensional image constructed from the height data and corresponding image plane coordinates. The measurement repeatability is better than 0·5 nm r.m.s. for a surface height range of 100 μm.

Three-dimensional imaging by sub-Nyquist sampling of white-light interferograms

We demonstrate a simple way of increasing the data acquisition and processing speed in a scanning white-light interferometer for surface topography measurement. The method consists of undersampling interference data and processing the resultant sub-Nyquist interferograms in the frequency domain to create complete three-dimensional images. Experimental results on a 20-μm step height standard show a measurement repeatability of 10 nm.