Month: July 2021

Cell refractive index is a key biophysical parameter, which has been extensively studied. It is correlated withother cell biophysical properties including mechanical,electrical and optical properties, and not only repre-sents the intracellular mass and concentration of a cell,but also provides important insight for various biolog-ical models. Measurement techniques developed earlieronly measure the effective refractive index of a cellor a cell suspension, providing only limited information on cell refractive index and hence hindering its in-depth analysis and correlation. Recently, the emergenceof microfluidic, photonic and imaging technologieshas enabled the manipulation of a single cell and the 3D refractive index of a single cell down to sub-micronresolution, providing powerfultoolstostudycellsbasedonrefractiveindex.Inthisreview,weprovideanoverview of cell refractive index models and measurement techniques includingmicrofluidic chip-basedtechniques for the last 50 years, present the applications and significance of cell refractive index in cell biol-ogy, hematology, and pathology, and discuss future research trends in the field, including 3D imagingmethods, integration with microfluidics and potential applications in new and breakthrough research areas.

ABSTRACT

Based on full wave simulations, ∼0.3 λ and ∼0.24 λ imaging resolutions can be achieved for incoherent transverse and longitudinal point dipoles, respectively, when the dipoles are on an aluminum oxide base with a fused silica microsphere as the imaging lens. These high spatial resolutions (better than 0.5 λ) can be attributed to almost 90° light acceptance angle of the microsphere and the solid immersion effects from the microsphere/base material. These simulation results can explain the ≳0.3 λ and ≳0.24 λ minimum resolvable center to center separation distance for thin metallic nanostructures and elongated metallic nanostructures, respectively, which is equal to ≳0.1–0.14 λ edge to edge distance observed in previous microsphere imaging experiments.

From the standpoint of the wave theory, we discuss the problem of an optical image formation created by a
virtually converging electromagnetic wave from a light source. We solved a diffraction problem of a point
source in a dielectric sphere. Formulas are obtained describing the virtual image of a point source in dielectric
sphere, in the parameter range where the approximation of geometric optics is not valid. For slits in an opaque
screen, the virtual image in the dielectric sphere allows the resolution of slits spaced from each other at distances much smaller than the diffraction limit λ/2. This explains the previously obtained experimental results
[Z. B. Wang, W. Guo, L. Li, B. Luk’yanchuk, A. Khan, Z. Liu, Z. Chen, and M. H. Hong, Nat. Commun.
2, 218 (2011)] on the super resolution effect with virtual image.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-28-3-3505&id=426218

Metasurfaces have recently emerged as a promising technology to realize flat and ultra-thin optical elements that can manipulate light at sub-wavelength scale. The typical design flow of a metasurface involves tedious Finite Difference Time Domain (FDTD) simulations followed by creation of a GDSII layout of the metasurface phase profile, the latter being essential for fabrication purposes. Both these steps can be time-consuming and involve the usage of expensive software. To make the design process more straightforward, we have developed an open-source software called MetaOptics built using Python for designing a generic metasurface optical element. MetaOptics uses the FDTD simulated phase response data of a set of meta-atoms and converts the phase profile of any given optical element into a metasurface GDSII layout. MetaOptics comes with in-built FDTD data for most commonly used wavelengths in the visible and infrared spectrum. It also has an option to upload user-specific dimension versus transmission phase data for any choice of wavelength. In this work we describe the software’s framework and provide details to guide users to design a metasurface layout using MetaOptics.