Abstract
Coherence scanning interferometry (CSI), a type of interference microscopy, has found broad applications in the advanced manufacturing industry, providing high-accuracy surface topography measurement. Enhancement of the metrological capability of CSI for complex surfaces, such as those featuring high slopes and spatial frequencies and high aspect-ratio structures, requires advances in modeling of CSI. However, current linear CSI models relying on approximate surface scattering models cannot accurately predict the instrument response for surfaces with complex geometries that cause multiple scattering. A boundary elements method is used as a rigorous scattering model to calculate the scattered field at a distant boundary. Then, the CSI signal is calculated by considering the holographic recording and reconstruction of the scattered field. Through this approach, the optical response of a CSI system can be predicted for almost any arbitrary surface geometry.
Highlights
Common reconstruction methods include the envelope detection method,[9,10] which estimates the surface height from the coherence envelope’s center or peak; methods that rely on frequency-domain analysis,[11,12] which obtain a more refined surface estimation by acquiring and combining both envelope and phase information through Fourier transform of the fringes; and the correlogram correlation method,[13] which through correlation to a reference signal can identify the location of coherence profile
The objective of this paper is to demonstrate a new way of modeling Coherence scanning interferometry (CSI) images using a boundary element methods (BEMs)-based rigorous surface scattering model and synthesizing images in k-space
The coherence envelope of the fringes slightly differs between the experimental results and those from the CSI model, which is expected due to the 2-D limitation of the BEM modeling and because the instrument’s source spectrum is not exactly Gaussian
Summary
Detailed information about a part’s surface topography is valuable, with a surface’s roughness, texture, and form determining functional macroscopic properties such as friction, adhesion, lubrication, and wear.[1,2,3,4] Coherence scanning interferometry (CSI) is a high precision surface topography measurement method, achieving surface measurement noise levels in the subnanometer range for planar and relatively smooth surfaces[5] while accurately handling much rougher surfaces.[6,7] As a CSI instrument scans, the interference between the light from the surface and reference mirror causes fringes to form, and these fringes are localized to the surface topography due to the low-coherence illumination used; by obtaining the fringes’ coherence envelope and phase, the surface topography can be estimated.[8] Common reconstruction methods include the envelope detection method,[9,10] which estimates the surface height from the coherence envelope’s center or peak; methods that rely on frequency-domain analysis,[11,12] which obtain a more refined surface estimation by acquiring and combining both envelope and phase information through Fourier transform of the fringes; and the correlogram correlation method,[13] which through correlation to a reference signal can identify the location of coherence profile
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