Development of an optical coherence tomographic surface profiling system with a wide scanning area based on telecentric F–θ imaging optics

Abstract

This study was conducted to develop an in situ tomographic profiling system that can detect surface defects over a wide area by applying a telecentric F–θ scanning optical system, with an effective measurement width of 200 mm, to a spectral domain optical coherence tomography (SD-OCT) system. A telecentric F–θ scanning optical system with an effective scanning length of up to 210 mm was designed. A focal depth up to 32 mm without loss of resolution was predicted when the entrance pupil diameter (EPD) was set to 4.0 mm. The obtained three-dimensional tomographic images of tire treads and scientific calculators confirmed the possibility of surface profiling for areas with a width of up to 200 mm and depth over 7 mm. Combining a large-area telecentric lens with an SD-OCT system made it possible to perform deep 3D profiling simultaneously with a large-area surface inspection. The developed surface tomographic profiling system can adjust the size of the EPD to achieve a resolution of less than 50 µm. It can thus provide axial and lateral resolutions equivalent to those of a conventional OCT system as well as a wide effective measurement area.