Although most of the mathematical models for cavitation in bearings provide reasonable estimates ... more Although most of the mathematical models for cavitation in bearings provide reasonable estimates of engineering parameters such as load capacity and friction, they are based on substantially different assumptions and further work is required to understand the fundamental operation of bearings. In this study digital holography was used to examine bubble formation within a glass sliding bearing. Digital holography collects the both the phase and amplitude of the transmitted wavefront and therefore contains quantitative information concerning the thickness of the cavitation bubbles. This paper introduces the experimental configuration and the digital holography system used to study cavitation. It also discusses the demodulation process and how the information can be used to find other interesting parameters such as bubble position and shape.
Coherence scanning interferometry (CSI) offers three-dimensional (3D) measurement of surface topo... more Coherence scanning interferometry (CSI) offers three-dimensional (3D) measurement of surface topography with high precision and accuracy. Defocus within the interferometric objective lens, however, is commonly present in CSI measurements and reduces both the resolving power of the imaging system and the ability to measure tilted surfaces. This Letter extends the linear theory of CSI to consider the effects of defocus on the 3D transfer function and the point spread function in an otherwise ideal CSI instrument. The results are compared with measurements of these functions in a real instrument. This work provides further evidence for the validity of the linear systems theory of CSI.
What is CSI? CSI is an increasingly popular optical method to provide fast high resolution measur... more What is CSI? CSI is an increasingly popular optical method to provide fast high resolution measurement of surface topography. Sub-nanometre axial resolution is achieved by measuring the phase of the field scattered from the surface of interest. Problem with metal surfaces Metal surfaces introduce phase offset due to their complex refractive indices in the measured scattered field. For a composite surface (surface made of more that one material, containing metals) surface topography would be changed. Microellipsometry Single point measurement of complex refractive indices of metal surfaces has been investigated with microellipsometry [1-2]. Phase at the back focal plane of a high-NA objective is measured by interferometric technique and is compared with ellipsometry data. He-Ne laser λ/2 beam expander L BS CCD BFL Mirau objective sample Fig. 3 Polarisation sensitive CSI Fig. 1 Commercially available CSI a) Taylor Hobson and (b) Zygo (a) (b) Fig. 2 Microellipsometry set-up References:...
ABSTRACT Tilt Scanning Interferometry (TSI) has been recently developed as an experimental method... more ABSTRACT Tilt Scanning Interferometry (TSI) has been recently developed as an experimental method to measure multi-component displacement fields inside the volume of semitransparent scattering materials. It can be considered as an extension of speckle interferometry in 3D, in which the illumination angle is tilted to provide depth information, or as an optical diffraction tomography technique with phase detection. It relies on phase measurements to extract the displacement information, as in the usual 2D counterparts. A numerical model to simulate the speckle fields recorded in TSI has been recently developed to enable the study on how the phase and amplitude are affected by factors such as refraction, absorption, scattering, dispersion, stress-optic coupling and spatial variations of the refractive index, all of which may lead to spurious displacements. In order to extract depth-resolved structure and phase information from TSI data, the approach had been to use Fourier Transformation of the intensity modulation signal along the illumination angle axis. However, it turns out that a more complete description of the imaging properties of the system for tomographic optical diffraction can be achieved using a D representation of the transfer function in k-space. According to this formalism, TSI is presented as a linear filtering operation. In this paper we describe the transfer function of TSI in 3D k-space, evaluate the 3D point spread function and present simulated results.
ABSTRACT When using dimensional measuring instruments it is assumed that there is a property of t... more ABSTRACT When using dimensional measuring instruments it is assumed that there is a property of the object, which we call surface, that is present before during and after the measurement, i.e. the surface is a fundamental property of an object that can, by appropriate means, be used to measure geometry. This paper will attempt to show that the fundamental property 'surface' does not exist in any simple form and that all the information we can have about a surface is the measurement data, which will include measurement uncertainty. Measurement data, or what will be referred to as the measured surface, is all that really exists. In this paper the basic physical differences between mechanically, electromagnetically and electrically measured surfaces are highlighted and discussed and accompanied by measurement results on a roughness artefact.
This paper describes the invention of an entirely new interferometric transducer for remote measu... more This paper describes the invention of an entirely new interferometric transducer for remote measurement of vibration acceleration. Compared to Laser Doppler Velocimetry, the device will offer more straightforward operation for the engineering user by incorporating an optical configuration in which path lengths are inherently matched. The Laser Doppler Accelerometer will complement use of piezo-electric accelerometers in all situations where noncontact
The cascaded correlator architecture comprises a series of traditional linear correlators separat... more The cascaded correlator architecture comprises a series of traditional linear correlators separated by nonlinear threshold functions, trained with neural-network techniques. We investigate the shift-invariant classification performance of cascaded correlators in comparison with optimum Bayes classifiers. Inputs are formulated as randomly generated sample members of known statistical class distributions. It is shown that when the separability of true and false classes is varied in both the first and the second orders, the two-stage cascaded correlator shows performance similar to that of the optimum quadratic Bayes classifier throughout the studied range. It is shown that this is due to the similar decision boundaries implemented by the two nonlinear classifiers.
Gao, F., Petzing, J, Coupland, JM and Leach, Richard K.(2007) Measurement of structured surface u... more Gao, F., Petzing, J, Coupland, JM and Leach, Richard K.(2007) Measurement of structured surface using stylus, AFM and optical methods. In: Metrology and properties of engineering surfaces: proceedings of the 11th international conference, Huddersfield, on 17th-20th July 2007. University of Huddersfield, Huddersfield, UK, p. 363. ISBN 1862180571
This guide describes good practice for the measurement and characterisation of rough surface topo... more This guide describes good practice for the measurement and characterisation of rough surface topography using coherence scanning interferometry (commonly referred to as vertical scanning white light interferometry). It is aimed at users of coherence scanning interferometry for the optical measurement of surface texture within production and research environments. The general guidelines described herein can be applied to the measurement of rough surfaces exhibiting different types of surface topography. For the purpose of this guide, the definition of a rough surface is one that has features with heights ranging from approximately 10 nm to less than 100 µm
ABSTRACT Tilt Scanning Interferometry (TSI) has been recently developed as an experimental method... more ABSTRACT Tilt Scanning Interferometry (TSI) has been recently developed as an experimental method to measure multi-component displacement fields inside the volume of semitransparent scattering materials. It can be considered as an extension of speckle interferometry in 3D, in which the illumination angle is tilted to provide depth information, or as an optical diffraction tomography technique with phase detection. It relies on phase measurements to extract the displacement information, as in the usual 2D counterparts. A numerical model to simulate the speckle fields recorded in TSI has been recently developed to enable the study on how the phase and amplitude are affected by factors such as refraction, absorption, scattering, dispersion, stress-optic coupling and spatial variations of the refractive index, all of which may lead to spurious displacements. In order to extract depth-resolved structure and phase information from TSI data, the approach had been to use Fourier Transformation of the intensity modulation signal along the illumination angle axis. However, it turns out that a more complete description of the imaging properties of the system for tomographic optical diffraction can be achieved using a D representation of the transfer function in k-space. According to this formalism, TSI is presented as a linear filtering operation. In this paper we describe the transfer function of TSI in 3D k-space, evaluate the 3D point spread function and present simulated results.
Although most of the mathematical models for cavitation in bearings provide reasonable estimates ... more Although most of the mathematical models for cavitation in bearings provide reasonable estimates of engineering parameters such as load capacity and friction, they are based on substantially different assumptions and further work is required to understand the fundamental operation of bearings. In this study digital holography was used to examine bubble formation within a glass sliding bearing. Digital holography collects the both the phase and amplitude of the transmitted wavefront and therefore contains quantitative information concerning the thickness of the cavitation bubbles. This paper introduces the experimental configuration and the digital holography system used to study cavitation. It also discusses the demodulation process and how the information can be used to find other interesting parameters such as bubble position and shape.
Coherence scanning interferometry (CSI) offers three-dimensional (3D) measurement of surface topo... more Coherence scanning interferometry (CSI) offers three-dimensional (3D) measurement of surface topography with high precision and accuracy. Defocus within the interferometric objective lens, however, is commonly present in CSI measurements and reduces both the resolving power of the imaging system and the ability to measure tilted surfaces. This Letter extends the linear theory of CSI to consider the effects of defocus on the 3D transfer function and the point spread function in an otherwise ideal CSI instrument. The results are compared with measurements of these functions in a real instrument. This work provides further evidence for the validity of the linear systems theory of CSI.
What is CSI? CSI is an increasingly popular optical method to provide fast high resolution measur... more What is CSI? CSI is an increasingly popular optical method to provide fast high resolution measurement of surface topography. Sub-nanometre axial resolution is achieved by measuring the phase of the field scattered from the surface of interest. Problem with metal surfaces Metal surfaces introduce phase offset due to their complex refractive indices in the measured scattered field. For a composite surface (surface made of more that one material, containing metals) surface topography would be changed. Microellipsometry Single point measurement of complex refractive indices of metal surfaces has been investigated with microellipsometry [1-2]. Phase at the back focal plane of a high-NA objective is measured by interferometric technique and is compared with ellipsometry data. He-Ne laser λ/2 beam expander L BS CCD BFL Mirau objective sample Fig. 3 Polarisation sensitive CSI Fig. 1 Commercially available CSI a) Taylor Hobson and (b) Zygo (a) (b) Fig. 2 Microellipsometry set-up References:...
ABSTRACT Tilt Scanning Interferometry (TSI) has been recently developed as an experimental method... more ABSTRACT Tilt Scanning Interferometry (TSI) has been recently developed as an experimental method to measure multi-component displacement fields inside the volume of semitransparent scattering materials. It can be considered as an extension of speckle interferometry in 3D, in which the illumination angle is tilted to provide depth information, or as an optical diffraction tomography technique with phase detection. It relies on phase measurements to extract the displacement information, as in the usual 2D counterparts. A numerical model to simulate the speckle fields recorded in TSI has been recently developed to enable the study on how the phase and amplitude are affected by factors such as refraction, absorption, scattering, dispersion, stress-optic coupling and spatial variations of the refractive index, all of which may lead to spurious displacements. In order to extract depth-resolved structure and phase information from TSI data, the approach had been to use Fourier Transformation of the intensity modulation signal along the illumination angle axis. However, it turns out that a more complete description of the imaging properties of the system for tomographic optical diffraction can be achieved using a D representation of the transfer function in k-space. According to this formalism, TSI is presented as a linear filtering operation. In this paper we describe the transfer function of TSI in 3D k-space, evaluate the 3D point spread function and present simulated results.
ABSTRACT When using dimensional measuring instruments it is assumed that there is a property of t... more ABSTRACT When using dimensional measuring instruments it is assumed that there is a property of the object, which we call surface, that is present before during and after the measurement, i.e. the surface is a fundamental property of an object that can, by appropriate means, be used to measure geometry. This paper will attempt to show that the fundamental property 'surface' does not exist in any simple form and that all the information we can have about a surface is the measurement data, which will include measurement uncertainty. Measurement data, or what will be referred to as the measured surface, is all that really exists. In this paper the basic physical differences between mechanically, electromagnetically and electrically measured surfaces are highlighted and discussed and accompanied by measurement results on a roughness artefact.
This paper describes the invention of an entirely new interferometric transducer for remote measu... more This paper describes the invention of an entirely new interferometric transducer for remote measurement of vibration acceleration. Compared to Laser Doppler Velocimetry, the device will offer more straightforward operation for the engineering user by incorporating an optical configuration in which path lengths are inherently matched. The Laser Doppler Accelerometer will complement use of piezo-electric accelerometers in all situations where noncontact
The cascaded correlator architecture comprises a series of traditional linear correlators separat... more The cascaded correlator architecture comprises a series of traditional linear correlators separated by nonlinear threshold functions, trained with neural-network techniques. We investigate the shift-invariant classification performance of cascaded correlators in comparison with optimum Bayes classifiers. Inputs are formulated as randomly generated sample members of known statistical class distributions. It is shown that when the separability of true and false classes is varied in both the first and the second orders, the two-stage cascaded correlator shows performance similar to that of the optimum quadratic Bayes classifier throughout the studied range. It is shown that this is due to the similar decision boundaries implemented by the two nonlinear classifiers.
Gao, F., Petzing, J, Coupland, JM and Leach, Richard K.(2007) Measurement of structured surface u... more Gao, F., Petzing, J, Coupland, JM and Leach, Richard K.(2007) Measurement of structured surface using stylus, AFM and optical methods. In: Metrology and properties of engineering surfaces: proceedings of the 11th international conference, Huddersfield, on 17th-20th July 2007. University of Huddersfield, Huddersfield, UK, p. 363. ISBN 1862180571
This guide describes good practice for the measurement and characterisation of rough surface topo... more This guide describes good practice for the measurement and characterisation of rough surface topography using coherence scanning interferometry (commonly referred to as vertical scanning white light interferometry). It is aimed at users of coherence scanning interferometry for the optical measurement of surface texture within production and research environments. The general guidelines described herein can be applied to the measurement of rough surfaces exhibiting different types of surface topography. For the purpose of this guide, the definition of a rough surface is one that has features with heights ranging from approximately 10 nm to less than 100 µm
ABSTRACT Tilt Scanning Interferometry (TSI) has been recently developed as an experimental method... more ABSTRACT Tilt Scanning Interferometry (TSI) has been recently developed as an experimental method to measure multi-component displacement fields inside the volume of semitransparent scattering materials. It can be considered as an extension of speckle interferometry in 3D, in which the illumination angle is tilted to provide depth information, or as an optical diffraction tomography technique with phase detection. It relies on phase measurements to extract the displacement information, as in the usual 2D counterparts. A numerical model to simulate the speckle fields recorded in TSI has been recently developed to enable the study on how the phase and amplitude are affected by factors such as refraction, absorption, scattering, dispersion, stress-optic coupling and spatial variations of the refractive index, all of which may lead to spurious displacements. In order to extract depth-resolved structure and phase information from TSI data, the approach had been to use Fourier Transformation of the intensity modulation signal along the illumination angle axis. However, it turns out that a more complete description of the imaging properties of the system for tomographic optical diffraction can be achieved using a D representation of the transfer function in k-space. According to this formalism, TSI is presented as a linear filtering operation. In this paper we describe the transfer function of TSI in 3D k-space, evaluate the 3D point spread function and present simulated results.
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