Highly focused beam generated with a height tuned micro-optical structure for high contrast microscopic imaging.

Light sheet illumination technology improves the signal-to-noise ratio, resolution, and reduces scattered backgrounds for biological microscopic detection system. Here, we developed a novel micro-optical structure to produce a focused and uniform beam for the enhancement of imaging contrast. The beam intensity and working distance can be modified by adjusting the height and period of the structure. Our experiments successfully recorded structured light illumination, demonstrating the ability of the structure to capture high-contrast imaging data. We compared the light fields generated with and without the structure to assess the imaging quality, revealing a maximum 4.78-fold improvement in the signal-to-noise ratio. This work provides a potential method for high-resolution and high-contrast light sheet fluorescence microscopic detection.

Combined simulation and experimental study on spectral absorbance of partially disordered MoSe2nanospheres.

It is important to clarify the role and possible applicability of partially disordered structures in photonics, but there is still a lack of an effective method for it. Here, we investigate partially disordered MoSe2nanospheres experimentally regarding their morphology and absorption spectrum in broadband wavelengths and propose an optical simulation with three-dimensional finite-difference time-domain method to explain the crucial impacts of morphological parameters on optical responses. The experimental spectral absorbance of MoSe2nanospheres reveals a strong light-absorbing character in broadband wavelengths. The simulated spectral curves coincide with the experimental results by adjusting morphological parameters, i.e. the statistics of size and the number of layer, and the linear correlation coefficient between the simulated and experimental spectral curves is up to 0.94. The disorder plays a key role in the high light-absorption feature, and the feature originates from anti-reflection, defective state absorption, multiple light scattering and coherent diffusion effects. The results not only deepen the understanding of disordered photonics in semiconductor nanostructures, but also provide a simulation approach to optimize experimental designs.

Lattice light sheets generated with a firmly arranged dielectric regular hexagonal pyramid array.

We present a firmly arranged dielectric regular hexagonal pyramid array to generate lattice light sheets with high conversion efficiency and low stray light. Both the size and working distance of the lattice light sheets can be modulated by changing the structural parameters. We experimentally recorded the lattice light sheets illumination, which is consistent with the corresponding simulation. To evaluate the imaging quality, we compared the light field generated with and without structure by using polystyrene fluorescent microspheres. This study provides a potential method for the building of light sheet fluorescence microscopy with high resolution and low phototoxicity.

Dynamic imaging of zebrafish heart with multi-planar light sheet microscopy.

Light sheet fluorescence microscopy has become a research hotspot in biomedicine because of low phototoxicity, high speed, and high resolution. However, the conventional methods to acquire three-dimensional spatial information are mainly based on scanning, which inevitably increases photodamage and is not real-time. Here, we propose a method to generate controllable multi-planar illumination with a dielectric isosceles triangular array and a design of multi-planar light sheet fluorescence microscopy system. We carry out experiments of three-dimensional illumination beam measurement, volumetric imaging of fluorescent microspheres, and dynamic in vivo imaging of zebrafish heart to evaluate the performance of this system. In addition, we apply this system to study the effects of bisphenol fluorene on the heart shape and heart-beating rate of zebrafish. Our experiment results indicate that the multi-planar light sheet microscopy system provides a novel and feasible method for three-dimensional selected plane imaging and low-phototoxicity in vivo imaging.

Saak Transform-Based Machine Learning for Light-Sheet Imaging of Cardiac Trabeculation.

OBJECTIVE: Recent advances in light-sheet fluorescence microscopy (LSFM) enable 3-dimensional (3-D) imaging of cardiac architecture and mechanics in toto. However, segmentation of the cardiac trabecular network to quantify cardiac injury remains a challenge. METHODS: We hereby employed "subspace approximation with augmented kernels (Saak) transform" for accurate and efficient quantification of the light-sheet image stacks following chemotherapy-treatment. We established a machine learning framework with augmented kernels based on the Karhunen-Loeve Transform (KLT) to preserve linearity and reversibility of rectification. RESULTS: The Saak transform-based machine learning enhances computational efficiency and obviates iterative optimization of cost function needed for neural networks, minimizing the number of training datasets for segmentation in our scenario. The integration of forward and inverse Saak transforms can also serve as a light-weight module to filter adversarial perturbations and reconstruct estimated images, salvaging robustness of existing classification methods. The accuracy and robustness of the Saak transform are evident following the tests of dice similarity coefficients and various adversary perturbation algorithms, respectively. The addition of edge detection further allows for quantifying the surface area to volume ratio (SVR) of the myocardium in response to chemotherapy-induced cardiac remodeling. CONCLUSION: The combination of Saak transform, random forest, and edge detection augments segmentation efficiency by 20-fold as compared to manual processing. SIGNIFICANCE: This new methodology establishes a robust framework for post light-sheet imaging processing, and creating a data-driven machine learning for automated quantification of cardiac ultra-structure.

Partially disordered nano-porous metallic oxide engineering: surface morphology controllability and multiple scattering properties.

Random multiple light scattering in disordered photonics leads to interesting and unexpected physical phenomena. Here, we demonstrate two types of partially disordered nano-porous metallic oxide materials: disordered grating nano-pores and two-dimensional disordered nano-tubes, which are produced just with one-step anodic oxidation. The relations among the processing parameters, morphology properties and multiple scattering characteristics are investigated. The surface morphology controllability can be achieved by simply changing the processing direct voltages, leading to different scattering properties. The probabilistic model of partially disordered nano-porous metallic oxide is constructed according to the nano-structure characteristics of oxide, and the rigorous coupled wave analysis is utilized for optical field simulation to exhibit the theoretical multiple scattering properties. Futhermore, the experimental scattering fields are measured and are analysed by statistical method. The research focuses on the disorder caused by one-step oxidation, which is distinct from previous studies that introducing disorder into periodic materials, and would open up new prospects for sensing, bionics and structural color.

All-Dielectric Meta-Surface for Multispectral Photography by Theta Modulation.

The traditional theta modulator encodes input information by superimposing Ronchi sub-gratings, which is extremely easy to cause spatial channel overlap that results in bands mixing. In this case, we present an all-dielectric theta modulation meta-surface with a new encoding method, which separates red, green, blue, and achromatic spatial channels on the focal plane. The meta-surface ensures that the positions of focal points are relatively consistent while focusing energy into the sub-wavelength regions. Our study offers a way to facilitate device miniaturization and system integration, which may have an important application in compact multispectral photography only with one detector.

Partially disordered TiO2 nanotube photonic crystal: randomness characterization and tuning of reflected scattering light.

Introducing disorder into a periodic nanostructure can lead to specific optical behaviors. We present a method of anodic oxidation by adjusting the applied voltage and process time to introduce disorder to TiO2 nanotubes. The surface morphology of TiO2 was numerically investigated according to the morphologies measured with a scanning electron microscope by imaging processing and a statistical method. TiO2 nanotubes obtained under different fabrication conditions have various tube radii ranging from 20-40 nm and wall thicknesses ranging from 20-70 nm. We also evaluated the degree of disorder of the tube radius of the TiO2 nanotubes. The reflected scattering light distributions of laser sources were optically measured at different observing distances, which indicate that the presence of nanotubes enhances the scattering effect, reducing the scattered light intensity by more than 75%, and provide the relationship between the scattering effect and surface morphology of nanotubes. This discovery offers TiO2 nanotubes important application prospects in optical limiting and light confinement, such as stealth coating.

Improvement of telescope resolution using a diffractive phase modulater.

Metasurface, fluorescent microscopy and scanning near-field optical microscopy can improve the resolution of microscopes remarkably, while the resolution of the telescope remains unimproved constrained by its giant objective lenses and distant targets. Here we put forward a way to raise the resolution of telescopes simply by adding a binary optical thin surface around its focal plane. Simulation results show that the surface can raise the image quality in the Cassegrain and Kepler telescope. By nano-lathe, we fabricated a designed binary surface and experiment it in the Kepler telescope. The results are consistent with those of simulation results. More details of the calibrated target are resolvable on the image plane after applying the binary optical surface. It proves that the binary optic surface can make contribute to the resolution of the telescope, thus is beneficial in astronomy, military surveillance field.

Visible-broadband Localized Vector Vortex Beam Generator with a Multi-structure-composited Meta-surface.

We demonstrate a vortex beam generator meta-surface that consists of silver structures and graphene layers. The miniature material is just a few microns in size and the working part is only a few hundred nanometers thick. With the incidence of the linearly polarized beam, the meta-surface generates high-localized vector vortex beam with a high proportion of the longitudinal component. Being compared with the constituent part of the meta-surface, the multi-structure-combined meta-surface increases the localization by 250% and the longitudinal component proportion by 200%. Moreover, the above artificial material can generate vortex beams in broadband within the visible light range. These novel optical properties have the potential to improve the precision and sensitivity of nanoparticle manipulation. The study serves as a foundation in optical miniaturization and integration, nanoparticle manipulation, high-efficiency optical and quantum communication, and light-driven micro-tools.

Vector vortex beam generation with dolphin-shaped cell meta-surface.

We present a dolphin-shaped cell meta-surface, which is a combination of dolphin-shaped metallic cells and dielectric substrate, for vector vortex beam generation with the illumination of linearly polarized light. Surface plasmon polaritons are excited at the boundary of the metallic cells, then guided by the metallic structures, and finally squeezed to the tips to form highly localized strong electromagnetic fields, which generate the intensity of vector vortex beams at z component. Synchronously, the abrupt phase change produced by the meta-surface is utilized to explain the vortex phase generated by elements. The new kind of structure can be utilized for communication, bioscience, and materiality.

Tuning of nanofocused vector vortex beam of metallic granary-shaped nanotip with spin-dependent dielectric helical cone.

We present the combined configuration of dielectric helical cone and metallic granary-shaped nanotip to produce three -dimensional vector vortex nanofocused optical field. The intensity and phase of the electric fields, and Povnting vector of the optical field generated by the combined configuration with linearly polarized illumination are studied with three-dimensional finite difference time-domain method. The localized vector electric field near the apex of the metallic granary-shaped nanotip is strongly depended on the chirality of the dielectric helical cone and the bottom radius of the metallic granary-shaped nanotip. The localized vector electric field is wavelength selective with the maximum intensity enhancement up to 104 times and minimum size of about 900 nm2, and the maximum radial electric field rotates 67.0° along z axis. This indicates the vector vortex beam generated by the combined configuration can be applied in nanofabrication, nano-sensing and nano-manipulation.

Modeling the specular spectral reflectance of partially ordered alumina nanopores on an aluminum substrate.

Anodizing of aluminum generates a porous alumina layer comprising cylindrical nanopores (300 nm diameter) extending essentially perpendicular to the substrate. The pore distribution over the surface exhibits a short-distance order close to hexagonal arrangement. On the contrary, long-distance order cannot be defined: the arrangement is not periodic. Visual observation of such nanoporous layers shows a reddish specular reflectance consistent with reflectance spectrum measurements. This work is a parametric study aiming at demonstrating that color effects are caused by the presence of disorder illustrated by the deviations from periodicity in terms of nanopore location and nanopore radius. Using the method of Rigorous Coupled Wave Analysis (RCWA), the reflectance spectrum has been simulated. Although our calculations were done using a simple one-dimensional (1D) model, a fair fit with experimental results is found.

Subwavelength B-shaped metallic hole array terahertz filter with InSb bar as thermally tunable structure.

We propose a subwavelength B-shaped metallic hole array filter with an embedded thermally tunable InSb semiconductor bar in the terahertz regime. The resonance frequency of this filter can be actively tuned by controlling the temperature of InSb. The transmissions of the filter are calculated with the finite-difference time domain method at various temperatures. Narrowband THz wave with the full width at half maximum of 235 GHz can be selected in the frequency range from 0.74 to 2.02 THz at temperatures from 160 to 350 K.

Microaxicave: inverted microaxicon to generate a hollow beam.

We present an inverted structure of microaxicon, called a microaxicave, with periodic micro-conic-cave shapes, to generate circular hollow beams. A microaxicave is fabricated in a quartz substrate with the combination of direct laser writing and inductively coupled plasma etching. The hollow beam generated by the quartz microaxicave is directly recorded with a CCD camera, and the hollow beam is consistent with analysis by the diffraction theory.

Heuristic models for diffraction by some simple micro-objects.

Electromagnetic optics is normally expected to be the only appropriate approach to describe structures with features of just a few wavelengths. But in some cases, these structure can be well described by simple heuristic arguments relying on geometrical optics and on diffraction by known elementary primitives. Such an approach allows a better understanding of the involved physical phenomena and reduces the computation time. We investigate the case of a microcomponent with a triangular section by using two approximate models with increasing complexity and explore their limits as the size of the structure decreases. Results are compared with a rigorous electromagnetic approach and discussed on the basis of near-field and far-field diffraction patterns.

Hexagonal microlens array fabricated by direct laser writing and inductively coupled plasma etching on organic light emitting devices to enhance the outcoupling efficiency.

A hexagonal microlens array directly fabricated on an indium tin oxide glass substrate by the combination of direct laser writing and inductively coupled plasma etching is demonstrated to enhance the outcoupling efficiency of the organic light emitting devices, which can avoid the loss of photons and the mechanical and thermal deformations at the glass/microlenses interface. An atomic force microscope measurement indicates the contour of the fabricated hexagonal microlens is nearly an ideal part of a hemisphere. From the comparison with the operating OLED without a microlens array, the outcoupling efficiency is enhanced more than 40% with the hexagonal microlens array on the glass substrate, and the enhanced emission from the active area of the device with the hexagonal microlens array at the viewing angles from 0 degrees to 40 degrees can clearly be seen.

Design of transmission blazed binary gratings for optical limiting with the form-birefringence theory.

The structure of transmission blazed binary gratings for optical limiting is designed with the form-birefringence theory. This kind of grating has subwavelength features, can imitate the transmission blazed grating effectively, and has higher efficiencies than a transmission blazed grating with a subwavelength structure. The diffraction efficiencies are calculated and analyzed. For the normal incident light with 10.6 microm wavelength, the transmissivities for the designed grating at 0 degrees deviation angle for TE and TM polarizations are 0.05% and 5.09%, respectively, which are basically identical to the results of the finite-difference time-domain method. The diffraction efficiencies of the first transmitted order for TE and TM polarizations are 93.95% and 83.88%, respectively.

Diffraction analysis of blazed transmission gratings with a modified extended scalar theory.

An alternative interpretation of the diffraction of blazed transmission gratings with moderate structure period is proposed according to a modified extended scalar theory (MEST). The diffraction field on the bottom facet of the grating is considered to be the interference of four subfields investigated in the problem of diffraction of a plane wave by an infinite half-plane. It is observed that MEST gives the total field that agrees with rigorous coupled-wave analysis (RCWA), and the result is more reliable than that of extended scalar theory (EST). The MEST is still a ray-optical-based approximation approach, and the region of validity is compared with EST and RCWA.