Quality assessment of the optical thin films using line field spectral domain optical coherence tomography

In this study, the industrial inspection of optical thin film on touch screen panels was demonstrated using line field spectral domain optical coherence tomography. The conventional Fourier domain optical coherence tomography system requires a single scanner for two-dimensional cross-sectional images and two scanners for volumetric images. Our developed line field spectral domain optical coherence tomography has the advantage of needing only a single scanner for volumetric images, while two-dimensional cross-sectional images are obtained by the parallel acquisition of an illuminated line on a sample using an area camera. Further, the image acquisition speed was enhanced by implementing a high speed camera (340 frames per seconds) with improved quantum efficiency at near infrared region enabling two-fold frame rate. Cross-sectional and volumetric images were acquired to detect the internal sublayer defects in the optical thin films, which are difficult to observe using visual or machine vision-based inspection methods. The developed pseudo code for defect identification in optical thin films was well-utilized here for the defect inspection. The system characterization is demonstrated using United State Air Force (USAF) resolution target. The results indicate the possible application of the proposed system in touch screen panel inspection for the quality assurance of products at the consumer end.