Microsphere and microcylinder-assisted microscopy (MAM) has grown to an intensively studied optical far-field imaging technique over the last decade that overcomes the fundamental lateral resolution limit of a given microscope. However, the physical effects leading to resolution enhancement are still frequently debated. In addition, various configurations of MAMs operating in transmission as well as reflection mode are examined and results generalized. We present a rigorous simulation model of MAM and present a way to quantify the resolution simulatively. The lateral resolution is compared for microscope arrangements in reflection and transmission mode. Further, we discuss different physical effects with respect to their contribution to resolution enhancement. The results indicate that the effects affecting the resolution as well as the enhancement itself strongly depend on the arrangement of the microscope and the measurement object.
Various attempts have been discussed to overcome the lateral resolution limit and thus to enlarge the fields of application of optical interference microscopy. Microsphere-assisted microscopy and interferometry have proven that the imaging of structures well below Abbe’s resolution limit through near-field assistance is possible if microspheres are placed on the measured surface and utilized as near-field assisting imaging elements. The enhancement of the numerical aperture (NA) by the microspheres as well as photonic nanojets was identified to explain the resolution enhancement, but also whispering gallery modes and evanescent waves are assumed to have an influence. Up to now, to the best of our knowledge, there is no complete understanding of the underlying mechanisms and no model enabling to examine ideal imaging parameters. This contribution is intended to clarify how much the lateral resolution of an already highly resolving Linnik interferometer equipped with 100 × NA 0.9 objective lenses can be further improved by microspheres. Our simulation model developed so far is based on rigorous near-field calculations combined with the diffraction-limited illumination and imaging process in an interference microscope. Here, we extend the model with respect to microsphere-assisted interference microscopy providing a rigorous simulation of the scattered electric field directly above the sphere. Simulation and experimental results will be compared in the three-dimensional spatial frequency domain and discussed in context with ray-tracing computations to achieve an in-depth understanding of the underlying mechanism of resolution enhancement by the microsphere.
Various attempts have been discussed to overcome the lateral resolution limit and thus to enlarge the fields of application of optical interference microscopy. Microsphere assisted microscopy and interferometry have proven that the imaging of structures well below Abbe’s resolution limit through near-field assistance is possible if microspheres are placed on the measured surface and utilized as near-field assisting imaging elements. The enhancement of the numerical aperture by the microspheres as well as photonic nanojets were identified to explain the resolution enhancement, but also whispering gallery modes and evanescent waves are assumed to have an influence. Up to now, to the best of our knowledge there is no complete understanding of the underlying mechanisms and no model enabling to examine ideal imaging parameters. This contribution is intended to clarify, how much the lateral resolution of an already highly resolving Linnik interferometer equipped with 100x, NA 0.9 objective lenses can be further improved by microspheres. Our simulation model is based on rigorous near-field calculations combined with the diffraction limited illumination and imaging process in an interference microscope. Here, we extend the model with respect to microsphere assisted interference microscopy providing a rigorous simulation of the scattered electric field directly above the sphere. Simulation and experimental results will be compared in the 3D spatial frequency domain and discussed in context with ray-tracing computations in order to achieve an in-depth understanding of the underlying mechanism of resolution enhancement by the mircosphere.
In optical metrology various approaches have been made in order to push the physical limitations of lateral resolution in microscopic and interferometric devices. Microsphere-assisted interferometry enables the measurement of structures well below Abbe’s resolution limit. In order to give an approach for analyzing the obtained measurement data, this study shows the transfer behavior in the three-dimensional spatial frequency domain. With the construction of an Ewald sphere further insight into the role of microspheres in the imaging process can be obtained. For improved analysis, selective illumination is applied to the select those parts of the field of view where the microsphere is located. Further improvement is achieved by appropriate windowing of the measurement data.
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