Abstract: A method for characterising instrument error in a surface measurement instrument, comprising obtaining first calibration measurement data representing a known surface form of a first reference object and obtaining second calibration measurement data representing a known surface form of a second reference object. At least a portion of the second calibration measurement data represents a measurement range that overlaps with at least a portion of a measurement range of the first calibration measurement data. A common error function is obtained that characterises the instrument error.

Abstract: A method of characterizing the surface of an aspheric diffractive structure includes using a metrological apparatus to perform a measurement on the surface of the structure so as to provide a measurement profile representing the z-direction deviations of the surface of the structure; determining parameters relating to the aspheric and diffractive components of the aspheric diffractive structure; producing data having the determined parameters; and comparing the produced data with the measurement profile to determine residual error data.

Abstract: A method for characterising instrument error in a surface measurement instrument, comprising obtaining first calibration measurement data representing a known surface form of a first reference object and obtaining second calibration measurement data representing a known surface form of a second reference object. At least a portion of the second calibration measurement data represents a measurement range that overlaps with at least a portion of a measurement range of the first calibration measurement data. A common error function is obtained that characterises the instrument error.

Abstract: A method of calibrating a surface measurement instrument includes rotating a work piece having an undulating surface on a turntable of a metrological apparatus; measuring the surface of the work piece at a plurality of rotational positions; analyzing the results of the measurement to determine parameters describing an error causing characteristic of the metrological apparatus; and using the determined parameters to correct measurement data for the error causing characteristic of the metrological apparatus.

Abstract: A multiphase meter for use in the quantification of the individual phase fractions of a multiphase flow has: a resonant cavity through which, in use, a multiphase fluid flows, a signal generator configured to apply electromagnetic energy at a range of frequencies to the cavity, and an enhancing and/or suppressing facility for enhancing and/or suppressing resonant modes of a signal produced resultant to the application of electromagnetic energy to the cavity.

Abstract: A stylus is deflected as a tip of the stylus follows surface variations along a measurement path on a surface of a workpiece. A transducer provides measurement data in a measurement coordinate system. A data processor is configured to: determine a relationship between the data in the measurement coordinate system and nominal surface data representing the expected surface characteristic of the workpiece in a workpiece coordinate system; simulate a measurement data set for the nominal surface using the nominal surface data and the determined relationship; if a simulated range of the simulated data set does not meet a given criterion, adjust a selected measurement data value for a selected point and repeat the simulation to determine an adjusted data value for which the simulated range meets the criterion; and determine start conditions required for a measurement procedure to provide the adjusted data value for the selected measurement point.

Abstract: A computer implemented method of determining the surface shape of an aspheric object using a metrological apparatus includes positioning the object on a support surface of a turntable so that an axis of the object is tilted with respect to the axis of rotation of the turntable; using a measurement probe to make a first measurement of the object; rotating the turntable; after rotation of the turntable, using a measurement probe to make a second measurement of the object, diametrically opposite the first measurement, estimating a first angle based on fitting the first measurement data using a surface model including: a dependency on the axis tilt angle and a dependency on the radius of the base of the object; estimating a second angle based on fitting the second measurement data to the surface model; and determining the tilt angle based on the first angle and the second angle.

Abstract: Metrological apparatus and a confocal sensor for use in such apparatus are described. The confocal sensor (1) has an optical pinhole (11) adapted for letting through a light beam (2). An optical assembly of the sensor has a first lens (12) having a refractive profile (121) and a diffractive profile (122) and a second lens (13) having at least a refractive profile (131). The refractive profile (121) of the first lens (12) and the refractive profile (131) of the second lens (13) focus the light beam (2) into a focused beam (21). The diffractive profile (122) of the first lens (12) creates longitudinal chromatic aberration so that the focused beam (21) has a focal zone with a longitudinal depth (R).

Abstract: A metrological apparatus has a surface data determiner to determine from measurement data a measured surface roughness data set (150) representing measured surface roughness and including any vibration induced measurement error and a harmonic model provider (120) providing a harmonic model representing vibration-induced surface characteristics of the surface as a set of harmonic components selected based on a surface form of the surface of the workpiece. A surface roughness determiner (140) uses the harmonic model and the measured surface roughness data to obtain a modified surface roughness data set in which vibration induced measurement error is suppressed.

Abstract: A method of determining a correction parameter for use in effecting alignment of a component of a metrological apparatus in at least one direction is described which includes: positioning an artefact on a support surface of a turntable of the metrological apparatus so that a measurement surface of the artefact is asymmetric with respect to a rotation axis of the turntable in the at least one direction; using a measurement probe of the measurement instrument to make a first measurement of the measurement surface; rotating the turntable; using the measurement probe of the measurement instrument to make a second measurement of the measurement surface after rotation of the turntable; and determining a correction parameter from the first and second measurements.

Abstract: Light reflected by a sample surface region and a reference surface interfere. A detector senses light intensity at intervals during relative movement along a scan path between the sample surface and the reference surface to provide a series of intensity values representing interference fringes. A data processor receives first intensity data including a first series of intensity values resulting from a measurement operation on a surface area of a substrate and second intensity data including a second series of intensity values resulting from a measurement operation on a surface area of a thin film structure. A gain is determined for each thin film of the thin film structure. Substrate and apparent thin film structure surface characteristics are determined on the basis of the first and second intensity data, respectively. The apparent thin film structure surface characteristic is modified using the substrate surface characteristic and the determined gain or gains.

Abstract: A surface measurement instrument for obtaining surface characteristic data of a sample surface is described. Relative movement between a reference surface and a sample support is caused to occur while a sensor senses light intensity at intervals along a scan path to provide a series of intensity values representing interference fringes produced by a region of a sample surface during said relative movement and from which series of intensity values surface characteristic data can be derived. The sample support is both translatable and tiltable in at least one direction perpendicular to a scan direction so that the sample support can be both tilted to cause the scan path to be normal to the sample surface region and translated to compensate for translation movement due to the tilting.

Abstract: A method of calibrating a surface measurement instrument includes rotating a work piece having an undulating surface on a turntable of a metrological apparatus; measuring the surface of the work piece at a plurality of rotational positions; analysing the results of the measurement to determine parameters describing an error causing characteristic of the metrological apparatus; and using the determined parameters to correct measurement data for the error causing characteristic of the metrological apparatus.

Abstract: A method of characterising the surface of an aspheric diffractive structure includes using a metrological apparatus to perform a measurement on the surface of the structure so as to provide a measurement profile representing the z-direction deviations of the surface of the structure; determining parameters relating to the aspheric and diffractive components of the aspheric diffractive structure; producing data having the determined parameters; and comparing the produced data with the measurement profile to determine residual error data.

Abstract: A metrological instrument determines a surface profile or form of a surface (61) of a workpiece (60) by effecting relative movement between a probe (11, 12) and the surface (61) so that the probe follows and is displaced by changes in the surface topography. A measure of the displacement of the probe as it follows the surface is obtained by a displacement provider which may be an interferometric gauge (35). Instead of making a measurement along a single measurement path over the surface (61), respective measurements are made on sections (61d and 61e or 61g and 61h) of that measurement path to obtain corresponding measurement data sets and these measurement data sets are independently positioned or aligned to a reference data set. The reference data set may be obtained by a measurement made on another section (61c) of the measurement path (61), on another measurement path (61f) over another surface (62a and 62b) of the component or on another measurement path over a surface on which the component is located.

Abstract: A coherence scanning interferometer carries out: a coherence scanning measurement operation on a surface area using a low numeric aperture objective so that the pitch of the surface structure elements is less that the spread of the point spread function at the surface to obtain structure surface intensity data; and a coherence scanning measurement operation on a non-structure surface area to obtain non-structure surface intensity data. A frequency transform ratio determiner determines a frequency transform ratio related to the ratio between the structure surface intensity data and the non-structure surface intensity data. A structure provider sets that frequency transform ratio equal to an expression representing the electric field at the image plane of the interferometer in terms of surface structure element size (height or depth) and width-to-pitch ratio and derives the surface structure element size and width-to-pitch ratio using the frequency transform ratio.

Abstract: Light reflected by a sample surface region and a reference surface interfere. A detector senses light intensity at intervals during relative movement along a scan path between the sample surface and the reference surface to provide a series of intensity values representing interference fringes. A data processor receives first intensity data comprising a first series of intensity values resulting from a measurement operation on a surface area of a substrate and second intensity data comprising a second series of intensity values resulting from a measurement operation on a surface area of a thin film structure. A gain is determined for each thin film of the thin film structure. Substrate and apparent thin film structure surface characteristics are determined on the basis of the first and second intensity data, respectively. The apparent thin film structure surface characteristic is modified using the substrate surface characteristic and the determined gain or gains.

Abstract: A multiphase meter for use in the quantification of the individual phase fractions of a multiphase flow has: a resonant cavity through which, in use, a multiphase fluid flows, a signal generator configured to apply electromagnetic energy at a range of frequencies to the cavity, and an enhancing and/or suppressing facility for enhancing and/or suppressing resonant modes of a signal produced resultant to the application of electromagnetic energy to the cavity.

Abstract: Light reflected by a sample surface region and a reference surface interfere. A detector senses light intensity at intervals during relative movement along a scan path between the sample surface and the reference surface to provide a series of intensity values representing interference fringes. A data processor receives first intensity data comprising a first series of intensity values resulting from a measurement operation on a surface area of a substrate and second intensity data including a second series of intensity values resulting from a measurement operation on a surface area of a thin film structure. A gain is determined for each thin film of the thin film structure. Substrate and apparent thin film structure surface characteristics are determined on the basis of the first and second intensity data, respectively. The apparent thin film structure surface characteristic is modified using the substrate surface characteristic and the determined gain or gains.

Abstract: A coherence scanning interferometer carries out: a coherence scanning measurement operation on a surface area using a low numeric aperture objective so that the pitch of the surface structure elements is less that the spread of the point spread function at the surface to obtain structure surface intensity data; and a coherence scanning measurement operation on a non-structure surface area to obtain non-structure surface intensity data. A frequency transform ratio determiner determines a frequency transform ratio related to the ratio between the structure surface intensity data and the non-structure surface intensity data. A structure provider sets that frequency transform ratio equal to an expression representing the electric field at the image plane of the interferometer in terms of surface structure element size (height or depth) and width-to-pitch ratio and derives the surface structure element size and width-to-pitch ratio using the frequency transform ratio.