Dual Porosity-Enhanced Antireflection Coatings with Continuous Gradient.

Slope-tunable Si nanorod arrays (NRAs) were fabricated with colloidal lithography and reactive ion etching (RIE). Sharpened NRAs fabricated by increasing the SF6/O2 flow ratio during RIE exhibit enhanced antireflection (AR) and hydrophobic properties, which are attributed to the smooth gradient in the effective refractive index of NRAs, and the enlarged water/air interface of the water drops in the NRA layers, respectively. Enhanced AR characteristics via modifying the slope of NRAs are accompanied by broad-band working ranges, omnidirectionality, and polarization insensitivity. Detailed experimental and theoretical analysis of slope-tunable NRAs should benefit the development of various self-cleaning optoelectronic devices with efficient light management.

Anti‐reflection (AR) coatings designed for glass and other rigid, inorganic substrates are commercially available; however, these inorganic AR coatings tend to crack or delaminate on flexible substrates. A polymeric film with a gradient refractive index (GRIN) profile would make an ideal AR coating for flexible substrates, but such coatings are challenging to fabricate using traditional, solution‐based techniques. Emulsion‐based resonant infrared, matrix‐assisted pulsed laser evaporation (RIR‐MAPLE) offers a straightforward approach to enabling the desired GRIN profile in polymeric materials. Two homopolymers (polystyrene (PS) and poly(methyl methacrylate) (PMMA)) are deposited as a blend and one component (PMMA) is dissolved, leaving behind a porous PS film. The porosity and refractive index (RI) are controlled by the volume ratio of the two homopolymers in the film. Structural and optical characterizations, as well as comparison to modeled optical properties, confirm that porous films fabricated from polymer blends deposited by RIR‐MAPLE behave as effective media over most of the visible spectrum. While evidence for the partial collapse of the porous polymer networks is observed, the RI of the porous films is reduced from that of the bulk material. Importantly, these studies demonstrate that RIR‐MAPLE should enable broadband, omnidirectional, polymeric AR coatings appropriate for flexible substrates. image

We estimated the contribution of the gradient refractive index (GRIN) and lens surfaces to lens astigmatism and lens astigmatic angle as a function of age in human donor lenses. Human lenses were imaged, ex vivo, with 3D-spectral optical coherence tomography (OCT) and their back focal length was measured using laser ray tracing. The contribution of lens surfaces and GRIN to lens astigmatism were evaluated by computational ray tracing on the GRIN lens and a homogenous equivalent index lens. Astigmatism magnitude and relative astigmatic angle of and between lens surfaces, GRIN lens, and lens with homogeneous refractive index were evaluated, and all results were correlated with age. The magnitude of astigmatism in the anterior lens surface decreased with age (slope = -0.005 diopters [D]/y; r = 0.397, P = 0.018). Posterior surface astigmatism and lens astigmatism were not age-dependent. Presence of GRIN did not alter significantly the magnitude or axis of the lens astigmatism. The astigmatism of GRIN lens and lens with homogeneous refractive index correlated with anterior lens surface astigmatism (GRIN, P = 3.9E - 6, r = 0.693; equivalent refractive index lens, P = 4.1E - 4, r = 0.565). The astigmatic angle of posterior surface, GRIN lens, and homogeneous refractive index lens did not change significantly with age. The axis of lens astigmatism is close to the astigmatic axis of the anterior lens surface. Age-related changes in lens astigmatism appear to be related to changes in the anterior lens astigmatism. The influence of the GRIN on lens astigmatism and the astigmatic axis is minor.

Based on the radiosonde data during the years 1957-1960, the effective earth's radius and the exponential model of atmospheric refractive index over coastal stations of India have been deduced. The correlation coefficient the least squares straight line fit between the gradient of refractive index in the lowest one kilometer D N and near the ground surface, NS has been studied and compared with the earlier studies based on the data of one year. The radio climatology of refractive index at 900-mb level and that of DN and their diurnal variation have also been briefly described.

Gradient refractive index (GRIN) lenses have been widely used for many applications. However, the traditional manufacturing methods of GRIN lenses are very time-consuming and only suitable for macro-scale operations. In addition, those methods do not have the ability to produce other GRIN optical components with complex refractive index profiles like aspheric or freeform components. We report here an approach to produce GRIN micro-optical components in chalcogenide glass based on a direct laser writing technique. Using this approach, we are able to locally modulate the refractive index of the glass subtrates and create an arbitrary refractive index profile. To prove the flexibility of the method for the production of GRIN micro-optics, we fabricated GRIN micro-lenses and a micro-Fresnel axicon (Fraxicon). The optical properties of micro-lenses can be controlled by varying the writing parameters or the substrate thickness. As a result, the working distance of the micro-lenses can extend from 0 to more than 1000 μm. Also, the micro-Fraxicon exhibits the ability to convert a Gaussian beam to a Bessel-like beam which concentrates the mid-infrared light into an approximately 1200 μm long confinement zone.

For use in lighting applications, white organic light-emitting devices (WOLEDs) must operate at higher biases to ensure an ample flux. However, stressed operation voltages often result in poor performance and limited device lifetime. This could be addressed by modifying the inherent optical properties of OLEDs. This study proposes a gradient refractive index (GRIN) substrate to adjust the ratio of the light-waveguided modes as well as the radiation mode. An embedded nanocomposite film consisting of titanium dioxide (TiO2) nanoparticles (NPs) was inserted between ITO and glass to create an internal light-extraction structure (IES). The high refractive index of TiO2 is essential for increasing the refractive index of the photoresist film and thus diminishing the total internal reflection between the interfaces. In addition, the silicon dioxide NPs mixed poly(dimethylsiloxane) was used to form an external light-extraction structure (EES). The refractive indices of the IES and EES were adjusted to form a GRIN substrate. Compared with a control device, this sophisticated substrate produced a 1.6 fold efficiency improvement. Furthermore, the experiment results indicates that the size of NPs in the nanocomposite layer affects the efficiency enhancement of OLEDs with different emission colors.

Cytopathic effects (CPEs) are a hallmark of infections. CPEs are difficult to observe due to phototoxicity from classical light microscopy. We report distinct patterns of virus infections in live cells using digital holo-tomographic microscopy (DHTM). DHTM is label-free and records the phase shift of low-energy light passing through the specimen on a transparent surface with minimal perturbation. DHTM measures the refractive index (RI) and computes the refractive index gradient (RIG), unveiling optical heterogeneity in cells. We find that vaccinia virus (VACV), herpes simplex virus (HSV), and rhinovirus (RV) infections progressively and distinctly increased RIG. VACV infection, but not HSV and RV infections, induced oscillations of cell volume, while all three viruses altered cytoplasmic membrane dynamics and induced apoptotic features akin to those caused by the chemical compound staurosporine. In sum, we introduce DHTM for quantitative label-free microscopy in infection research and uncover virus type-specific changes and CPE in living cells with minimal interference.IMPORTANCE This study introduces label-free digital holo-tomographic microscopy (DHTM) and refractive index gradient (RIG) measurements of live, virus-infected cells. We use DHTM to describe virus type-specific cytopathic effects, including cyclic volume changes of vaccinia virus infections, and cytoplasmic condensations in herpesvirus and rhinovirus infections, distinct from apoptotic cells. This work shows for the first time that DHTM is suitable to observe virus-infected cells and distinguishes virus type-specific signatures under noninvasive conditions. It provides a basis for future studies, where correlative fluorescence microscopy of cell and virus structures annotate distinct RIG values derived from DHTM.

Coupled radiation and solidification heat transfer inside a graded index medium by finite element method

Scalable, robust, omnidirectional antireflective, superhydrophobic coatings based on chitin nanofibers for efficient solar energy collection.

Plasmonic and phase transition has been blended to gain the infrared radiative switching which is tunable with temperature or voltage supply. This is applied via vanadium dioxide, tungsten trioxide, and molybdenum trioxide as transition metal oxides (TMO). The metallic phase at high temperature or colored state contributes in magnetic polariton (MP) excitation, producing broad absorptance. The TMO-based sub-layer is integrated underneath the grating fully supporting MP resonance. In contrast, this underlayer leads to producing the narrowband absorptance originated from concept of zero contrast grating (ZCG). The zero gradient in refractive index at the output plane of the grating cause transmission of light in broad wavelength range. With introduction of reflective silver underlayer, those transmitted through the grating are reflected back. However, there exists the near-zero narrowband transmission peaks in ZCG. This undergoes transformation to narrowband absorptance. In addition, another absorptance peak can be induced due to phonon modes at insulating phase. The MP resonance at metallic phase is characterized with inductor-capacitor (LC) circuit and the narrowband absorptance peaks are characterized with phase shift from the Fabry–Perot round trip (FP-RT) eigenequation from high contrast grating (HCG). The work expands the usage of transition metal oxides in infrared region with larger contrast.

This manuscript evaluates the use of an actively cooled aerodynamic probe body with integrated optics to perform short focal length laser diagnostics within high-temperature, high-supersonic flows. A novel probe with a “ship’s bow” shape and an open cycle cooling scheme ending in a matrix of effusion holes is presented. The flow around the probe is studied numerically using 3D Steady Reynolds-Averaged Navier-Stokes (RANS) simulations at Mach 6, with free stream total conditions of 1700 K and 44.2 bar. The laser trajectory is calculated using the ray propagation equation to ensure that it deviates minimally while going through regions of gradients in refractive index. The location and shape of the detached shock formed ahead of the probe is extracted, and the minimum focal length achievable for measurement of the undisturbed flow-field is determined. The sensitivity of the bow shock shape to changes in cooling pressure between 1.33 and 1.835 bar, and to blocked holes has been computed. Finally, the flow through the effusion system of the probe is tested experimentally, ensuring its proper operation, and checking the consistency of the effusion boundary conditions used in the numerical study.

Bi-AGRIN cemented doublets, super corrected for zero axial color, spherical aberration and sphero-chromatism can show polychromatic performance in the range of 0.004 waves PV or better at the red and blue wavelengths for speeds up to F/2. These doublets are comprised of two elements of axial gradient index glass. The crown and flint elements are each designed with separate and distinct gradient glass lines, giving each element an axial gradient in refractive index and dispersion. This paper examines one design and its performance sensitivity to dispersion modeling via the Buchdahl and Sellmeier dispersion equations.

Reflection losses at optical interfaces are detrimental for many applications in optics and optoelectronics. Antireflection coatings (ARCs) are typically based on the principle that light reflected at the ARC’s interfaces interferes destructively to maximise light transmission. Advances in the fabrication of porous thin films have enabled to achieve refractive indices low enough to meet conditions for zero-reflectance off substrate materials like glass. Yet, many widespread applications require robustness and self-cleaning of ARCs, as well as low processing temperatures and compatibility with plastic substrates. In this chapter a new concept is presented which relies on the use of a high molecular weight block copolymer system with a large volume fraction of the hydrophobic block in combination with silica sol-gel chemistry. Spontaneous dense packing of colloidal micelles results in the co-assembly of the inorganic material in an inverse-opal like morphology. Subsequent removal of the polymer host leads to robust and continuous inorganic films with refractive indices as low as 1.13. The polymer-driven self-assembly route to ultralow refractive index films enables to replace up to 50 w% silica with high refractive index photocatalytic TiO2 nanocrystals, which freely disperse within the inorganic network. The resulting ARCs show good optical and self-cleaning properties and can be processed onto flexible plastic substrates.

Transient temperature response in semitransparent variable refractive index medium subjected to a pulse irradiation

Microwave propagation through an electric-field-coupled metamaterial lens with a refractive index gradient is experimentally investigated. A gradient in the refractive index of the metamaterial is introduced by continuous tuning of a single parameter in the metamaterial elements. Experimental field maps, acquired in a planar waveguide, demonstrate that the planar gradient index lens can be used to collimate radiation from a line source, thereby forming a beam.