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.