Engineered bacteria that self-assemble "bioglass" polysilicate coatings display enhanced light focusing.

Photonic devices are cutting-edge optical materials that produce narrow, intense beams of light, but their synthesis typically requires toxic, complex methodology. Here we employ a synthetic biology approach to produce environmentally-friendly, living microlenses with tunable structural properties. We engineered Escherichia coli bacteria to display the silica biomineralization enzyme silicatein from aquatic sea sponges. Our silicatein-expressing bacteria can self-assemble a shell of polysilicate "bioglass" around themselves. Remarkably, the polysilicate-encapsulated bacteria can focus light into intense nanojets that are nearly an order of magnitude brighter than unmodified bacteria. Polysilicate-encapsulated bacteria are metabolically active for up to four months, potentially allowing them to sense and respond to stimuli over time. Our data demonstrate that engineered bacterial particles have the potential to revolutionize the development of multiple optical and photonic technologies.

Computational refocusing in phase-resolved confocal microscopy.

We demonstrate numerical refocusing in coherent confocal laser scanning microscopy based on synthetic optical holography. In this physics-based approach, computational propagation is implemented on the complex signal recovered in synthetic holography, consistent with wave physics and the parameters of the microscope. An experimental demonstration is shown to restore an in-focus image of a test object from data acquired at several focal plane off-sets. Numerical refocusing can provide focused views on samples with large height variation, with a potential application in confocal optical surface profiling.

100 years of Emil Wolf: introduction.

The groundbreaking research and ideas introduced by Emil Wolf continue to inspire researchers and motivate ongoing research in the wave properties of light. This special issue commemorates the legacy of Emil Wolf with research in physical optics, with specific focus on those areas where Wolf was active, such as optical coherence theory, inverse problems, singular optics, imaging, and polarization, and the intersection of these fields of study. Here we discuss the life of Emil Wolf and his influence on optical science and the optics community.

Suppression of the conjugate signal for broadband computed imaging via synthetic phase modulation.

We present synthetic-phase-modulated interferometric synthetic aperture microscopy (SPM-ISAM), a method to perform 3D object reconstructions from data acquired with confocal broadband interferometric microscopy (BIM) that reconstructs images virtually free of coherent and depth-dependent defocus artifacts. This is achieved by implementing a sinusoidal SPM method in combination with an ISAM reconstruction algorithm that uses relatively low-modulation frequencies compared with acquisition frequencies. A theoretical framework and numerical results are provided here.

Resolution Limit in Infrared Chemical Imaging.

Chemical imaging combines the spatial specificity of optical microscopy with the spectral selectivity of vibrational spectroscopy. Mid-infrared (IR) absorption imaging instruments are now able to capture high-quality spectra with microscopic spatial detail, but the limits of their ability to resolve spatial and spectral objects remain less understood. In particular, the sensitivity of measurements to chemical and spatial changes and rules for optical design have been presented, but the influence of spectral information on spatial sensitivity is as yet relatively unexplored. We report an information theory-based approach to quantify the spatial localization capability of spectral data in chemical imaging. We explicitly consider the joint effects of the signal-to-noise ratio and spectral separation that have significance in experimental settings to derive resolution limits in IR spectroscopic imaging.

Math, color, and new additions to the team: editorial.

Editor-in-Chief P. Scott Carney introduces the Journal's newest Topical Editors, John Schotland and Minchen Wei.

Extraordinary Fluorescence Enhancement in Metal-Dielectric Core-Shell Nanoparticles.

We show that in metal-dielectric core-shell nanoparticles, unusually thick dielectric coatings can produce extreme fluorescence enhancement with an enhancement factor F̅ ≳ 3000 for emitters located on the surface or in the interior of the shell of Au@dielectric spherical particles under realistic conditions, even for the emitters with 100% intrinsic quantum yield. Thick dielectric coatings facilitate high-quality transverse electric (TE) multipole (l = 7) resonances which are shown as the major cause for the reported extraordinary values of F̅.

2020 JOSA A Emerging Researcher Best Paper Prize: editorial.

JOSA A Editor-in-Chief P. Scott Carney, Feature Editor Johannes Courtial, and members of the 2020 Emerging Researcher Best Paper Prize Committee announce the recipient of the 2020 prize for the best paper published by an emerging researcher in the Journal.

Optics in your part of the world and a new Topical Editor joins the team: editorial.

Editor-in-Chief P. Scott Carney introduces the Journal's newest Topical Editor, Angela Dudley.

Photons to the left, photons to the right, photons down under: editorial.

Editor-in-Chief P. Scott Carney introduces the Journal's newest Topical Editor, Arti Agrawal.

2019 JOSA A Emerging Researcher Best Paper Prize: editorial.

JOSA A Editor-in-Chief P. Scott Carney and Feature Editor Johannes Courtial announce the recipient of the 2019 prize for the best paper published by an emerging researcher in the Journal.

Intriguing branching of the maximum position of the absorption cross section in Mie theory explained.

A potential control over the position of maxima of scattering and absorption cross sections can be exploited to better tailor nanoparticles for specific light-matter interaction applications. Here we explain in detail the mechanism of an appreciable blue shift of the absorption cross-section peak relative to a metal spherical particle localized surface plasmon resonance (LSPR) defined as the maximum of the extinction (and scattering) cross section. Such a branching of cross sections' maxima requires a certain threshold value of size parameter (x≈0.7 for dipole channel) and is a prerequisite for obtaining high fluorescence enhancements, because the spectral region of high radiative rate enhancement becomes separated from the spectral region of high non-radiative rate enhancement. A consequence is that the maximum of the absorption cross section cannot be used as the definition of the LSPR position for x≳0.7.

New Feature Editor and Topical Editor: editorial.

Editor-in-Chief P. Scott Carney introduces the Journal's new Feature Editor and newest Topical Editor.

Plasmonic nano-shells: atomistic discrete interaction versus classic electrodynamics models.

Using the extended discrete interaction model and Mie theory, we investigate the tunability of the optical polarizability of small metallic nano-shells. We show that the spectral positions of symmetric and antisymmetric dipolar plasmon resonances vary with the ratio of particle radius to hole radius in a manner similar to one predicted for uniform metallic nano-shells using a semiclassical approach of two coupled harmonic oscillators. We show that, according to the extended discrete interaction model, the dipolar plasmon resonances are also present for nano-shells in the 2-13 nm size region and show the same functional dependence seen for larger nano-shells. Using previously fitted data from experiment, we can predict the size-dependence of the plasma frequency for nano-shells in the 1-15 nm size region. We find that Mie theory, which utilizes the electron mean free path correction for the permittivity, is not able to reproduce the same functional form of the dipolar modes for the nano-shells of the same sizes.

Fellows, visionary and atmospheric, and a new addition to the team: editorial.

Editor-in-Chief P. Scott Carney congratulates recent awardees and introduces the Journal's newest Topical Editor.

All-digital histopathology by infrared-optical hybrid microscopy.

Optical microscopy for biomedical samples requires expertise in staining to visualize structure and composition. Midinfrared (mid-IR) spectroscopic imaging offers label-free molecular recording and virtual staining by probing fundamental vibrational modes of molecular components. This quantitative signal can be combined with machine learning to enable microscopy in diverse fields from cancer diagnoses to forensics. However, absorption of IR light by common optical imaging components makes mid-IR light incompatible with modern optical microscopy and almost all biomedical research and clinical workflows. Here we conceptualize an IR-optical hybrid (IR-OH) approach that sensitively measures molecular composition based on an optical microscope with wide-field interferometric detection of absorption-induced sample expansion. We demonstrate that IR-OH exceeds state-of-the-art IR microscopy in coverage (10-fold), spatial resolution (fourfold), and spectral consistency (by mitigating the effects of scattering). The combined impact of these advances allows full slide infrared absorption images of unstained breast tissue sections on a visible microscope platform. We further show that automated histopathologic segmentation and generation of computationally stained (stainless) images is possible, resolving morphological features in both color and spatial detail comparable to current pathology protocols but without stains or human interpretation. IR-OH is compatible with clinical and research pathology practice and could make for a cost-effective alternative to conventional stain-based protocols for stainless, all-digital pathology.

Turning the page: editorial.

Editor-in-Chief P. Scott Carney introduces the Journal's newest Topical Editors, Irina V. Larina and Jonathan Petruccelli.

Doing good by writing well for JOSA A: editorial.

Editor-in-Chief P. Scott Carney gives his thoughts on good writing for scientific publication.

Success is in the air for JOSA A: editorial.

Editor-in-Chief P. Scott Carney introduces the Journal's newest Topical Editor, Svetlana Avramov-Zamurovic.

Electromagnetic energy in multilayered spherical particles.

We obtain exact analytic expressions for (i) the electromagnetic energy radial density within and outside a multilayered sphere and (ii) the total electromagnetic energy stored within its core and each of its shells. Explicit expressions for the special cases of lossless core and shell are also provided. The general solution is based on the compact recursive transfer-matrix method, and its validity includes also magnetic media. The theory is illustrated on examples of electric field enhancement within various metallo-dielectric silica-gold multilayered spheres. The user-friendly MATLAB code, which includes the theoretical treatment, is available as a supplement to the paper.