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
A single shot RGB Multi-wavelength Polarizing Interferometer (MPI) is proposed for measuring moving precision surfaces with micro/nano-scale structured pattern or defects. The interferometer is combined with four CMOS cameras, each with an integrated Bayer filter, to capture four color phase shifted interferograms at a single exposure time. The phase shifting mechanism is achieved by using thin film linear polarizers and birefringent quarter-wave plates. The 2π phase ambiguity range is extended by using a synthetic wavelength produced from the RGB. Measurement of step height standard samples are also presented and compared to measurement obtained by Coherence Scanning Interferometer (CSI).
Film processing procedures by means of Roll-to-Roll (R2R) for barrier coatings can often result in PV barrier films being manufactured with significant quantities of defects, which results in lower efficiency and a short life span. In order to improve the process yield and product efficiency, it is desirable to develop an inspection system that can detect transparent barrier film defects in the production line during film processing. Off-line detection of defects in transparent PV barrier films is difficult and time consuming. Consequently, implementing an accurate in-situ defects inspection system in the production environment is even more challenging, since the requirements on positioning, fast measurement, long term stability and robustness against environmental disturbance are demanding. This paper reports on the development and deployment of two in-situ PV barrier films defect detection systems, one based on wavelength scanning interferometry (WSI) and the other on White Light Channeled Spectral Interferometry (WLCSI), and the integration into an R2R film processing line at the Centre for Process Innovation (CPI). The paper outlines the environmental vibration strategy for both systems, and the developed auto-focusing methodology for WSI. The systems have been tested and characterised and initial results compared to laboratory-based instrumentation are presented.
The assessment of surface finish has become increasingly important in the field of precision engineering. Optical
interferometry has been widely used for surface measurement due to the advantages of non-contact and high accuracy
interrogation. In spite of the 2π; phase ambiguity that can limit the measurement scale in monochromatic interferometry,
other optical interferomtry have succeeded to overcome this problem and to measure both rough and smooth surfaces
such as white light interferometry and wavelength scanning interferometry (WSI). The WSI can be used to measure large
discontinuous surface profiles by producing phase shifts without any mechanical scanning process. Where the WSI
produces the phase shifts by altering the wavelength of a broadband light source and capturing the produced
interferograms by a CCD. This paper introduces an optical setup and operation principle of a WSI that used a halogen
white light as a broadband illumination source and an acousto-optic tunable filter (AOTF) as a wavelength scanning
device. This setup can provide a wide scan range in the visible region. The scanned range is being operated from 682.8
nm to 552.8nm and the number of captured frames is 128. Furthermore, the obtained interferograms from a Linnik
interferometer have been analyzed by two methods, Fast Fourier Transform and Convolution. A mathematical
description of both methods is presented then a comparison in results accuracy is made between them. The Areal
measurement of a standard 4.707μm step height sample shows that FFT and convolution methods could provide a
nanometer measurement resolution for the surface finish inspection.
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