A tetragonal barium titanate (BTO) thin film of high crystal quality with a c-axis oriented out of the plane was successfully grown at 500℃ on the strontium titanate(100) substrate using the physical vapor deposition technique. It showed epitaxial growth with a dense morphology and a low full width at half maximum value (FWHM) of 0.5° in the X-ray diffraction spectroscopy rocking curve measurements of the BTO(002) reflection. Using a modified Sénarmont method, the birefringence measurement of the BTO film revealed that it predominantly exhibits a quadratic and asymmetric electrooptic (EO) behavior in response to the applied DC electric field with an effective EO coefficient value of 1.94 × 10^-19 m²/V², providing useful insights on the BTO growth and its potential optoelectronics applications.

We present an athermal resonant metasurface created by periodically coupled subwavelength structures in an engineered membrane. In this approach, we propose a bilayer metasurface structure with opposite thermo-optic coefficients to compensate for the undesired spectral shift caused by thermal effects. By creating a bilayer metastructure with different thermo-optic coefficients, thermally-induced spectral shifts could be minimized, thus allowing for a nearly temperatureinsensitive resonant metasurface. The working principle of the proposed metasurface is based on the epitaxial engineering of the coupled subwavelength structures in the metasurface to cancel the temperature-dependent resonant wavelength shift. To demonstrate the proposed thermal compensation concept, Fano-type guided mode resonance will be used as an optical probe in a TiO₂/Si composite film. The proposed athermal resonant metasurface offers great potential for many applications, such as free-space optical communications, metasurface-based optical sensing, imaging, filters, and modulators.

Polymer banknotes are being increasingly adopted to replace older banknotes. Since banknotes are forensically important substrates for fingermark detection and identification, we present a single-step process to enhance the visualization of fingermarks on banknotes using 40-nm-thick columnar thin films (CTFs) of nickel. This singlestep vacuum technique enhances the quality grade of fingermarks maximally, whether the fingermarks are aged for one or seven days before CTF deposition. This work represents progress over currently available sequences of diverse techniques for enhancing fingermarks on polymer banknotes.

There is an ongoing critical discussion about whether long-term durability of polymer optics can be guaranteed after passing accelerated tests, as the degradation mechanisms are very complex. Thick scratch resistant antireflective coatings AR-hard and antireflective nanostructured coatings AR-plas had been developed several years ago. The polymer substrates are exposed to plasma emissions and ion bombardment both during coating and structuring. On the other hand, cycloolefin-based polymers may undergo structural changes induced by plasma. For the present study, it was possible to re-examine coated samples a long time after their production. Various AR coatings and different cyclic olefin polymers were re-evaluated in terms of their optical properties and coating adhesion.

Polycrystalline diamond grown via chemical vapor deposition is a widely used optical material due to its extremely broad transmission window that extends from the visible through the far infrared. Random and periodic anti-reflective (AR) surface structures etched directly into the substrate provide an all-diamond solution for transmission enhancement without sacrificing the material’s unparalleled thermal conductivity. While periodic AR micro-structures (ARMs) can be lithographically fabricated with AR bandwidths exceeding 20 microns, their implementation at scale is hindered by the numerous manufacturing steps required. More recently, a single-step plasma-based process was developed for etching Randomly distributed Anti-Reflective nano-structures (RAR) into mono- and polycrystalline diamonds, with high transmission at wavelengths ranging from visible to longwave infrared (LWIR). With both approaches, the lack of dissimilar material unlocks the material’s full potential in various applications in the LWIR, such as IR spectroscopy and high-power lasers for extreme ultraviolet (EUV) generation. This work presents optical measurements of two-surface RAR nano-structures and single-surface periodic ARMs etched into polycrystalline diamond windows. The tradeoffs and advantages of each texture design will be discussed. Data for single-part, intra-batch, and inter-batch uniformity will highlight the scalability of RAR nano-textured diamond to commercial production levels.

Silicon (Si) photodiodes play a crucial role in complementary metal-oxide-semiconductor (CMOS) image sensors, particularly in visible cameras, and are increasingly in demand for infrared or short-wavelength (SWIR) cameras in modern autonomous vehicles operating under various weather conditions. However, the bandgap energy of 1.12eV in Si limits its capability to detect light in the infrared range, only allowing visible light detection. In this study, we propose transparent, quantum-thickness, Schottky-junction photodiodes on Si for light detection from visible to SWIR wavelengths. We employ an atomically thin TiO₂ interfacial layer between an n-type Si substrate and a nanometer-thick metallic layer, which is positioned beneath a transparent conductive oxide (TCO) layer, to create n-Si/TiO₂/TiN/ITO multilayered Schottky-junction photodiodes. Without the typical p-n junction in Si, we observed photocurrents through interband transitions by incident photons in the wavelength range of 400 ~ 1,100nm. Additionally, small but noticeable amounts of photocurrent were also measured by internal photoemission (IPE) via hot carrier generation even at the wavelength of 1,310nm. The embedded TiO₂ layer significantly reduced dark current by two orders of magnitude with little change in photocurrent or quantum efficiency. This can be attributed to the low conduction band offset of the TiO₂ semiconductor, which contributes to a quantum tunneling barrier without changing the Schottky barrier height and disturbing the internal photoemission process.

Motivated by the need for reliable optical sensing modalities, we fabricated a doubly chiral sculptured thin film (D-CSTF) of zinc selenide, comprising a structurally left-handed CSTF and a structurally right-handed CSTF deposited consecutively on a glass substrate. Both constituent STFs were sufficiently thick as to exhibit the circular Bragg phenomenon independently and distinctly in the 500–900-nm wavelength range. The fabrication process involved asymmetric serial bideposition through thermal evaporation. All eight circular remittances of the D-CSTF were measured using a variable-angle spectroscopic system. The direction of the incident light was varied so that the azimuthal angle ranged from 0◦ to 70◦ and the polar angle from 0° to 180°. The D-CSTF functions as a bandstop filter for RCP light as well as a bandstop filter for LCP light, regardless of the polar angle and the face that is illuminated, the two stopbands being distinct from each other.

To generate the shortest high power laser pulse, a single-cycle pulse, gratings inside the ultrafast laser’s compressor and stretcher need to meet three requirements: high efficiency, ultra-broad bandwidth, and high damage threshold. These three requirements are especially difficult to meet for Infrared (IR) lasers. We have demonstrated for the first time that combination of E-beam lithography and anisotropic wet etching of silicon wafers can produce gratings meeting the three requirements. A global optimization approach is used to achieve diffraction efficiency > 90% for mid IR gratings centered at 5μm with a 65% relative bandwidth, which is 1.47x (2.1x) lager than required by Gaussian-shaped (sech²-shaped) single-cycle pulses. A similar high-efficiency mid-IR grating was recently fabricated and tested, demonstrating an efficiency of 92.0% at 4.3μm, which closely matches the designed efficiency of 94.5%. Conformal coatings in fabrication and large angle of incidence in design are employed to improve damage threshold. Further enhancement of the grating performance has been realized through a double-blazing feature, combining the classic triangular groove geometry with a “land-ridge” modulation. The design methodology has been applied to near IR and long IR successfully to prove that the new design approach and fabrication technology combined is a reliable way to make gratings for single-cycle high-power ultrafast laser for entire IR region (0.8μm – 20μm).

The effect of various thicknesses (6nm-74nm) on the optical, electrical, and surface topology properties of Tin-doped Indium Oxide (ITO) thin conductive films (TCF) on Si and glass substrates has been studied. The ITO thin films were prepared by direct-current (DC) sputtering at room temperature using 1-meter diameter high vacuum coating chamber at GSFC. The Ar partial pressure was 2 × 10^-3 Torr and DC power was kept at 200W. The film resistivity was measured by a four-point probe method at room temperature. Transmittance of ITO films on glass were characterized in the 200-2500nm range through optical spectrophotometry. Optical properties (n, k) were derived through ellipsometry. The surface topology and morphology were examined by scanning white light interferometry (SWILI) and atomic force microscopy (AFM). As an exemplary result, the transmittance of glass substrate coated with a 22.9 nm thick ITO thin film, normalized to the transmittance of the bare glass substrate, is 0.985 at λ=550nm and 0.988 at λ=1064nm. This sample presents a resistivity of 7.29 × 10^-4 Ω-cm, and a surface roughness of 0.4 nm.

When a laser beam is scanned over a material multiple times, periodic surface structures, known as laser-induced periodic surface structures (LIPSSs) are formed. In this study, a 355-nm ultraviolet laser with a Gaussian beam was scanned over a 45-nm-thick amorphous-Si layer at the maximum fluence of 115mJ/cm², resulting in the creation of periodic Si nanoparticles of approximately 50nm size. The measured transmittance of incident light with a polarization angle between transverse magnetic (TM) and transverse electric (TE) showed bumps at wavelength of 400-500nm and 690nm. The periodic surface was modeled as a 1D grating and analyzed using numerical simulation. Cross-sectional plots of electric and magnetic field distributions at peak wavelengths revealed strong localization in the grating region of the Si layer, suggesting that the bumps originate from guiding modes localized at the surface Si layer. Additionally, birefringence measured in ultraviolet-visible wavelength range using a standard polarizer-analyzer setup was enhanced at the corresponding wavelengths. This birefringence can be controlled by adjusting laser processing parameters, offering additional applications to polarization-sensitive printing, flat optics, optical data storage, and sensing devices.

Scientists have conducted studies for replicating structural color, characterized by bright and vivid colors that arise from colorless micro- or nano-structures. The periodic nanostructures, known as photonic crystals, found in particular creatures in nature have been studied for their ability to achieve structural colors. However, the complex architecture and structure of photonic crystals with structural light present significant fabrication challenges to mimic these vivid colors. Recent research has discovered that a single nanopillar can produce colors through Mie resonance, which makes it possible to create ultra-high-resolution colored structural light through the patterning of nano-sized pillars. However, these fabricated nanopillars present the given colors. In other words, predetermined designs is lack of the tuning function. Here, we show a method based on two-photon polymerization to realize 3D printed nano-pillar structures of Liquid Crystal Networks (LCN). This material undergoes shape changes in response to light or temperature variations, allowing for a tunable full-color palette, achieving nano-scale, high-resolution color-changing patterns.

Silicon Photonics is today one of the most important technologies around the world due to its level of maturity which can offer huge innovative designs and new integrated systems to be applied in several research fields such as optics communications, sensing, medicine, and aerospace, among others. Due to a growing need to develop compact sensors capable of acquiring biological and environmental measurements, optical and spectroscopic methods are the most promising approaches to reach the requirements of this type of sensor. Although there are some compact spectroscopic sensors based on free-space optical systems, further miniaturization, and weight reduction while maintaining high wavelength resolution is still a challenge. To overcome these issues, Arrayed Waveguide Gratings (AWG) present qualities and characteristics that can satisfy both requirements.

This work presents a useful procedure to design an integrated sensor under the SOI platform for applications in the NIR/MIR infrared band. Based on multiple AWGs in combination with other key photonic devices such as: double-ring resonators, thermal phase shifters, waveguide tapers, and others, an innovate sensor can be designed. The proposed strategy allows us to optimize specific characteristics of the spectral response to match the absorption spectrum of the element to be detected, as well as the footprint of this passive sensor. This goal can be reached using a full study of the key design parameter dependence for every optical circuit used. We have validated the carried-out methodology with this device and optimized the AWG designs for sensing applications.

This work investigates the creation of nanostructured glass surfaces through the solid-state thermal dewetting of gold (Au) thin films, followed by the removal of the resulting Au nanoisland (AuNI) to form craters on the glass substrate. By varying the nominal thickness of the Au film and the annealing time, we controlled the size, density, and distribution of the AuNI, which in turn affected the dimensions of the resulting craters. Characterization of these nanostructured surfaces was performed using SEM and AFM analyses, revealing significant variations in the lateral and vertical characteristics. Experimental reflectivity measurements showed up to a 20% reduction, demonstrating the tunability of the nanostructured surfaces. The Maxwell-Garnett model (MGM) was employed to theoretically model the optical properties of these surfaces, treating the craters as air-filled cylinders. The MGM parameters, including the thickness of the nanostructured layer and the filling fraction of the cylinders, were derived to match experimental data. Further theoretical optimization indicated that achieving craters with a depth of approximately 100nm could further reduce reflectivity. This tunability in nanostructuring enables the design of glass surfaces with specific optical properties, making the findings promising for applications such as solar cells, where minimizing Fresnel losses is crucial.

This work investigates the reflectance properties of nanostructured glass surfaces modeled as random monolayers of air spheres embedded in a glass matrix. The study employs three analytical models: the Maxwell-Garnett Model (MGM), the 2D Dipole Model (2-DMM), and the Coherent Scattering Model (CSM). All models predicted a decrease in reflectance due to the nanostructuring of the glass surface. This decrease in reflectance is particularly significant, reaching up to almost 20% across the entire visible spectrum, for nanostructures with 15% surface coverage and crater radii of 50nm. Each model’s suitability, advantages, and limitations are discussed in the context of varying particle sizes and surface coverages.

Flexible electronics have achieved a lot of attraction due to the increasing demand in the market. Single wall carbon nanotube (SWCNT) with semiconducting properties is one of the major players in this sector due to its flexibility, high carrier mobility, superb electrical properties, and consistent mechanical properties. The application of printing technology in flexible electronics has grown significantly in recent years, as these methods are easy to use, inexpensive, and work with a variety of materials which become an attractive choice for fabricating large-area electronic devices within a noticeably abbreviated time. Among all the printing technologies, Aerosol jet printer can print high resolution, precise electronic devices with minimum ink usage. However, the most challenging parts of this printing technology are the high mobility semiconducting layer and the thin pinhole free dielectric layer. In this work we will demonstrate the method of fabricating CNT field effect transistor (CNTFET) using Aerosol jet technique to find out the best possible outcome in terms of higher on/off switching ratio and lower gate threshold voltage. Due to these properties of the printed CNTFET, it can be used as several types of applications such as switching devices, sensors, radio frequency amplification and other various flexible electronic wearable devices.