KEYWORDS: Confocal microscopy, Finite element methods, Microscopes, 3D modeling, Modeling, Near field, Near field optics, Polarization, Scattered light, Optical simulations
We present three digital twins for microscopy capable of simulating the image formation, the back focal plane formation and the near-field of confocal microscopes. For this, the light-surface interaction and the near-field are simulated using three different rigorous methods, the finite element method, the Fourier modal method and the boundary element method. The back focal plane formation and the image formation are simulated using three different Fourier optics implementations. The microscope modelling is done for ideal optical components, but can be extended to non-ideal optical components if the details of the optical components are known. The three models provide high accuracy and advantages with respect to the computational effort as a full 3D model is applied to 2D structures and the lateral scanning process of the confocal microscope is considered without repeating the time consuming rigorous simulation of the scattering process. The accuracy of the models are proven by comparison of the methods.
Photonic nanojets (PNJs) are highly localized optical probes that promise label-free measurements beyond the classical diffraction limit. We here demonstrate numerically the feasibility of label-free, self-calibrating, super-resolution optical detection and imaging using far-field scatterometry in conjunction with rapid scanning photonic nanojet excitation achieved with no opto-mechanical intervention. We realize PNJ scanning by computed structured illumination of refractive dielectric micro-elements such as micro-spheres and micro-cubes. Our far-field measurement data are phaseless. In proof-of-concept computations, we use our steerable optical probe to extract information on nanoparticles, aggregates of nanoparticles, and thin-film structures beyond the classical lateral and vertical resolution limits, in the presence of supporting structures such as substrates.
We present a numerical computation scheme for calculation of the reflected and transmitted near- and far-fields arising from the interaction of 2D cylindrical shaped particles with photonic structures. The photonic structures are illuminated with either planar or Gaussian incident fields. The interaction between the cylindrical particle and the photonic structure is generally too complex to be handled analytically, so we will use the semi-analytical Fourier Modal Method (FMM) to calculate the near- and far-fields. The Gaussian field is written as a sum of plane waves with varying amplitudes. We present a very general method for obtaining the plane wave amplitudes by combining the angular spectrum theory, Parseval’s theorem and Shannon’s sampling theorem. We demonstrate the use of this method in our rigorous calculation of reflected and transmitted near- and far-fields of single cylindrical particle located in the vicinity of a periodic photonic structure or a planar silicon surface. The examples demonstrate that the method may be applied to particle counting.
KEYWORDS: Nanoparticles, Thin films, Near field optics, Microscopy, Interfaces, Super resolution, Dielectrics, Photonic nanostructures, Optical microscopy, Near field
The lateral and vertical resolution in conventional optical microscopy is restricted by fundamental diffraction limits. One direction towards super-resolution optical microscopy is the use of photonic nanojets (PNJs) for sample illumination. Here, the aim is to exploit the high spatial localization of PNJs to allow measurements of sub-classical particles and features in spite of their small size compared to the operating wavelength. The applications of super-resolution methods include fluorescence and Raman microscopy, scatterometric measurements, and optical imaging. As a step towards PNJ scanning microscopy, we here apply our recently proposed method for fast and precise steering of PNJs over a large dynamical range in the near field. In a proof-of-concept computation, we use the steerable optical probe to extract information on structures beyond the classical lateral and vertical resolution limits.
Accurate scatterometry and ellipsometry characterization of non-perfect thin films and nanostructured
surfaces are challenging. Imperfections like surface roughness make the associated modelling and
inverse problem solution difficult due to the lack of knowledge about the imperfection on the surface.
Combining measurement data from several instruments increases the knowledge of non-perfect
surfaces. In this paper we investigate how to incorporate this knowledge of surface imperfection into
inverse methods used in scatterometry and ellipsometry using the Rigorous Coupled Wave Analysis.
Three classes of imperfections are examined. The imperfections are introduced as periodic structures
with a super cell periods ten times larger than the simple grating period. Two classes of imperfections
concern the grating and one class concern the substrate. It is shown that imperfections of a few
nanometers can severely change the reflective response on silicon gratings. Inverse scatterometry
analyses of gratings with imperfection using simulated data with white noise have been performed. The
results show that scatterometry is a robust technology that is able to characterize grating imperfections
provided that the imperfection class is known.
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