Hybrid FDTD-Fresnel Modeling of the Scanning Confocal Microscopy

摘要

Scanning confocal microscopy is a widely recognized technique due to its applicability to the imaging of 3D geometries. Image formation in this technique is often analyzed using the Fresnel approximation. However, such an approximation is not sufficient when object dimensions are comparable to the operating wavelength and, most of all, when the target is composed of different semi-transparent materials. Yet, this is very typical for modern integrated circuits where we work with subwavelength features. In such a case target needs to be modeled using full-wave Maxwell theory. However, most of electromagnetic modeling methods (like well established FDTD method) become computationally impractical when the modeled scenario has dimensions measured in hundreds or even thousands of wavelengths like in the far-field microscopy. Therefore, in this paper we propose a hybrid approach that takes advantage of both FDTD and Fresnel approximation methods. The first method will be applied to the modeling of close vicinity of the target. The advantage of that is versatility in definition of arbitrarily shaped geometries as well as wideband approach of the FDTD method. Subsequently, results provided by the FDTD solver will be transferred to the procedure based on the scalar Fresnel approximation used to process the final image pixel by pixel. We will show that the presented method allows imaging of 3D shape of targets proving unique advantage of using FDTD method to the modeling of scanning confocal microscopy.