Manufacturing is progressing towards the utilisation of smart and autonomous manufacturing processes, facilitated by deeply integrated sensors providing rapid feedback, to enable tighter process control and ‘right first-time’ fabrication methods. Optical components are inherently heavy and bulky and consequently so is current optical instrumentation making it unsuitable to provide the in-situ measurements required to fully realise the vision of future manufacturing. Optical metasurfaces, being able to replicate the function of conventional optical elements, offer a step change in optical instrumentation size and weight. Here, we report on our monolithic metasurface confocal sensor that performs all the necessary optical manipulations to perform as an ultra-compact confocal sensor whilst also being rugged against misalignment. We have subsequently built on this approach to develop a tip-tilt displacement sensor which is achieved by interleaving three lenses into a single metasurface, each acting as a chromatic confocal sensor that is offset from each other.
The dispersive interferometry provides an instantaneous surface measurement in a single camera frame, making it resistant to environmental disturbances and ideal for in-process surface metrology. It also benefits from the extended measurement ranges in both depth and lateral directions by incorporating hyperspectral imaging technology and cylindrical beam illumination, respectively. This paper reports on an in-house developed cylindrical lens-based dispersive interferometer for high-accuracy surface inspection, particularly for structured surfaces. The obtained spectral interferogram is analyzed using the fringe order algorithm, in which the phase slope method is used to calculate the initial height to resolve the fringe order ambiguity and eventually an improved height value can be obtained using the exacted phase of a single wavelength. Experiments demonstrate that the measurement noise of the developed interferometry system is less than 1 nm within the measurement range. A brass step sample made by a diamond turning machine was measured and the experimental results closely align with those given by the commercial white light interferometer -Talysurf CCI 3000.
Thin film flexible electronics refer to a class of electronic devices built on flexible substrates. Examples includes printed Li batteries, Thin film flexible electronics refer to a class of electronic devices manufactured by multiple layering and scribing on flexible polymer substrates. Examples of such devices includes printed Li batteries, flexible photovoltaic cells and light emitting diodes. These devices are often mass manufactured by Roll-to-Roll processing (R2R). Whilst the basic technology is well established, the increasing demands on precision environmental protection and multi layering of devices means that in-process measurement of printed surface features is a critical bottle neck in terms of developing R2R as a process route. The purpose of the present paper is to review the current critical dimensional metrology needs in R2R manufacture and in particular to highlight the development of a new inprocess surface metrology system based on Multi-wavelength Polarizing Interferometry (MPI). The system is capable of measurement in real time, is environmentally robust and has nanometre resolution. The paper concludes by highlighting an example of the first trial implementation of the MPI on a production level R2R machine and discussed issues with quantification of film dimensions and associated signal processing
Polarized angle-resolved spectroscopy is introduced to measure transparent anisotropic films with back focal plane imaging by virtue of its rich information provided at various incident and azimuthal angles. The polarized angle-resolved spectroscopy provides a conoscopic interferogram and angle-resolved spectrum to deal with the complex characterization parameters of an anisotropic film, including the thickness, principal refractive index, and optical axis. Firstly, the optics model of a transparent anisotropic film is built by superpositioning the incoherent waves from the front and rear surfaces with coherency matrices formalism when the optical length is larger than the coherent length, and the incoherent issue arises. Then the optical axis of the anisotropic sample can be determined by the conoscopic interference image with the melatope, which marks zero phase difference between the ordinary and extraordinary waves. The measured angle-resolved reflectance spectrum and anisotropic interference phase are fitted to the optics model of the film with coherency matrix formalism, utilizing the Levenberg-Marquardt algorithm to calculate the thickness and dispersion principal refractive index within a single shot. The thickness and anisotropic refractive index are determined for sapphire and polyethylene terephthalate (PET) samples with our homemade polarized angle-resolved spectrometer. The thickness measurement results show that the relative error of the proposed method is less than 1.45%.
Surface reconstruction method plays an important role in many engineering fields. It is an imperative procedure to carry out surface reconstruction from measurement data in reverse engineering, which is complicated with the presence of outliers. To achieve better accuracy and robustness of reconstruction, an improved moving total least squares (MTLS) algorithm based on k-means clustering called KMTLS method is proposed in this article. KMTLS adjusts the weights of discrete points within the support domain by adopting a two-step fitting procedure. Firstly, ordinary least squares (OLS) method is adopted to obtain the pre-fitting result and calculate the residuals as the input of k-means clustering. In kmeans clustering, abnormal nodes are classified into one cluster and a weight function based on clustering information is introduced to deal with these nodes. Secondly, based on the compact weight function in MTLS and the weight obtained in the pre-fitting procedure, weighted total least squares method is conducted to determine the final estimated value. The process of detecting outliers is automatic without setting threshold artificially. The experiment shows that KMTLS has great robustness to outliers.
The line-scan dispersive interferometry (LSDI) benefits from single-shot measurement in nature and has potential to perform in-line surface metrology. In this technique, the interference beam produced by the two arms of the interferometer is spatially dispersed by a diffraction grating along the rows (or columns) of the CCD pixels. In which case, a two-dimensional spectral interferogram is generated. In this paper, fringe order determination is carried out to retrieve the more accurate phase information along the chromaticity axis of the interferogram and then the height map of the tested profile can be calculated with high resolution. Two standard artefacts have been evaluated using the developed LSDI and the experimental results are compared with that of phase slope method as well as the commercial instrument (Talysurf CCI 3000), which shows that better performance in measurement noise is achieved. Additionally, the measurement repeatability is significantly improved and demonstrated within sub-nanometer range.
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