On-line surface inspection using cylindrical lens-based spectral domain low-coherence interferometry

We present a spectral domain low-coherence interferometry (SD-LCI) method that is effective for applications in on-line surface inspection because it can obtain a surface profile in a single shot. It has an advantage over existing spectral interferometry techniques by using cylindrical lenses as the objective lens in a Michelson interferometric configuration to enable the measurement of long profiles. Combined with a modern high speed CCD camera, general-purpose graphics processing unit (GPGPU) and multi-core processors computing technology, fast measurement can be achieved. By translating the tested sample during the measurement procedure, real-time surface inspection was implemented, which is proved by the large-scale 3D surface measurement in this paper. ZEMAX software is used to simulate the SD-LCI system and analyse the alignment errors. Two step height surfaces were measured and the captured interferograms were analyzed using a fast Fourier transform algorithm. Both 2D profile results and 3D surface maps closely align with the calibrated specifications given by the manufacturer.