Spectral Domain Low- Coherence Interferometry for On-line Surface Inspection

We present an on-line surface measurement technique based on spectral domain low-coherence
interferometry (SD-LCI), which can obtain a one dimensional surface profile with just one shot. This technique has an advantage over existing spectral interferometry in the large scale measurement up to 10 mm in length along the tested surface by using a cylindrical lenses based interferometic objective. In this SD-LCI system, the white light interferogram is spectrally decomposed by a spectrometer to determine the phase, which is encoded as a function of wavenumber along the chromaticity axis. After the phase of the channelled spectral signals is calculated at all wavelengths
simultaneously, the optical path difference (OPD) is determined as the slope of the phase versus
wavenumber. By adding a lateral scanning or rotating the cylindrical lenses, large-scale areal
measurement is achieved as well. The experimental details of measurements on two surface samples
are presented and discussed in this paper.