Dissertation/Thesis Abstract

Microspherical Photonics for Enhancing Resolution of Optical Microscopy and Sensitivity of Focal Plane Arrays
by Brettin, Aaron, Ph.D., The University of North Carolina at Charlotte, 2018, 168; 10979114
Abstract (Summary)

It is shown that the resolution of virtual images of dye-doped dielectric nanospheres obtained through dielectric microspheres can be increased beyond the classical diffraction limit by decreasing the period of nanoplasmonic array used for localized plasmonic structured illumination of these objects. In addition, it is also shown that post-imaging processing, which represents an intrinsic part of structured illumination microscopy, is not required for achieving the super-resolved images. This observation is interpreted due to the fact that the radiation of objects placed at the surface of nanoplasmonic arrays with sufficiently short periods can be almost completely redirected into folded dispersions of nanoplasmonic array, so that the diffraction orders responsible for super-resolution are more efficiently coupled to dielectric microspherical antenna compared to that for the uncoupled radiative modes.

Focal plane arrays (FPAs) are pixelated arrays of photo detectors which are widely used for imaging. The problem of uncooled mid-wave infrared (MWIR) FPAs is related to their large thermal noise. In this work, it is demonstrated that the surface area and thermal noise of pixels can be reduced without sacrificing their sensitivity by using integration with dielectric microspheres, which can be achieved by a novel method of suction assembly of microspheres in microhole arrays. In addition, it is demonstrated that alternative solution of this problem is offered by integration with microconical light concentrators, which can be fabricated by various well-established technologies including the use of the Nanoscribe. Using a simplified two-dimensional (2D) model, it is studied how the photocurrent depends on the geometrical parameters of microcones and on the angle of incidence.

The photoinduced aggregation of nanoparticles is of interest for material science and nonlinear optics applications. Light-driven assembly of nanoplasmonic particles is observed as an optical memory effect taking place due to the aggregation of 20 nm gold nanoparticles in the illuminated regions of the substrate after full evaporation of the liquid suspension. It is shown that the level of photoexcitation intensity required for observation of this effect is several orders of magnitude smaller compared to that in the previous studies of photoinduced aggregation typically performed using intense laser illumination. It is also demonstrated in a preliminary way that the photoinduced aggregation is facilitated in the spectral range resonant with localized surface plasmon resonances in nanoparticles.

Inverse scattering algorithms are of interest for many applications; however, they are usually based on low refractive index contrast approximations and measuring the phase distributions. In contrast, Globally Convergent Inverse Scattering (GCIS) algorithms in principle should allow phaseless image reconstruction for high refractive index objects. In order to test the operation of GCIS algorithms, high-index (n~2) barium titanate glass microspheres were assembled directly at a silicon chip of a cell phone camera and the scattering patterns resembling the shape of the Airy disks were detected using a set of narrow spectral filters throughout a broad range of wavelengths in the visible regime. The results were found to be in a good agreement with the image calculations and can be used for the object reconstruction based on GCIS algorithms.

Indexing (document details)
Advisor: Astratov, Vasily N.
Commitee: Boreman, Glenn, Cifarelli, Victor, Fiddy, Michael, Nesmelov, Yuri
School: The University of North Carolina at Charlotte
Department: Optical Science & Engineering
School Location: United States -- North Carolina
Source: DAI-B 80/03(E), Dissertation Abstracts International
Subjects: Engineering, Optics
Keywords: Focal plane array enhancement, Inverse scattering, Microsphere nanoscopy, Photo induced aggregation, Super resolution
Publication Number: 10979114
ISBN: 978-0-438-68913-8
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