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This work presents a realistic, wave-optical signal modelling tool for chromatic confocal systems that employ partially incoherent illumination. In such systems, the partially incoherent illumination is obtained either via intrinsically partially coherent light sources or by propagating the light from a spatially coherent source through a multimode optical fibre of appropriate length and core diameter.
The practicality of our modelling approach has besides the coherent illumination likewise been demonstrated for systems that employ incoherent illumination. Where the confocal signal was obtained simply by the incoherent summation of the intensities of the reflected fields in the image/detector plane. But now in the case of partially coherent illumination, not only the amplitude but also the phase information is of utmost importance for the realistic modelling of the chromatic confocal signal.
In the literature review to the best of our knowledge, we have not come across a modelling approach for chromatic confocal signals that offers the possibility to preserve the phase information of all the modes that propagate through the conventional two-pass chromatic confocal optical system.
In this work, first, the number of propagating modes through the optical system is determined. Here the specifications of the light source such as spatial as well as spectral distribution of the light source and the illumination function received at the entrance of the chromatic confocal system play an important role. Secondly, all these modes for the complete wavelength range have to be propagated through the system based on the wave-optical model. Finally, for all wavelengths, the coherent summation is done in the image/detector plane using the amplitude and phase information.
The flexibility of this modelling approach is unprecedented and it not only offers a better understanding of chromatic confocal imaging but also opens new horizons in the areas such as artificial intelligence and machine learning where computer-assisted methods are employed that offer the realization of a more accurate, robust and eventually cost-efficient chromatic confocal measurement device.
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