This PDF file contains the front matter associated with SPIE Proceedings Volume 12796, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

This paper presents a machine-learning based approach to microwave ghost imaging. Unlike traditional imaging techniques, ghost imaging is a non-local imaging technique that does not involve scanning. Since ghost imaging uses a single detector at a fixed location, measurements are taken under various random or pseudo-random illuminations to recover the image. Moving from the optical frequency regime to the microwave regime, the accurate measurement of such a random field becomes more complicated because there is no device such as a Charge Coupled Device (CCD) camera at microwaves. In this work, we generate pseudo-random field patterns using a reconfigurable metasurface and we use a single detector at a fixed location to measure the reflection from the target. Reconfigurability plays a fundamental role in ghost imaging. The microstrip line-fed metasurface is formed by unit cells of size 2.564 × 1 mm², which are tuned by a pair of PIN diodes. By activating these diodes in forward or reverse bias, different field patterns can be generated. A receiver is placed in the centre of the aperture. The resonance frequency is set to 40 GHz. To recover the image, we present a machine-learning approach. A neural network is trained using a synthetic dataset obtained from ANSYS High Frequency Structure Simulator (HFSS) simulations to learn the second-order correlation between the incident field patterns and the measured scattered fields at the detector in order to recover the target image.

The Lateral Flow (LF) immunoassays in biosensing are universally applied for point-of-care disease monitoring purposes with gold nanoparticles (AuNPs). With a highlight on nanomaterial gold core-shells (AuCSs), here we characterise the conjugation of monoclonal antibodies (mAbs) with AuCSs in Cystatin C (CysC) diagnostics via Scanning Electron Microscopy (SEM), Dynamic Light Scattering (DLS), and Ultraviolet-Visible (UV-Vis) spectroscopy. Two formats AuCSs used in the conjugation include the lyophilised powder format (NHS-dried) and carboxyl surfaced particles in liquid form. The AuCSs’ performance was demonstrated by extracting the grey intensity of the LF test line (T) and control line (C) for respective areas under the curve calculation and T/C ratio (Test line intensity / Control line intensity). The translucent coloured AuCSs (NHS-dried) peak at 801 nm in UV-Vis with conjugated mAbs concentration at 357.8 μg/ml, the conjugated AuCSs hydrodynamic size maximize at 234.9 ± 9.7 nm, with 100 μg/ml mAbs. Similarly, the carboxyl surfaced AuCSs obtain the UV-Vis maximum absorption at 840 nm wavelength with mAbs concentration at 358 μg/ml. Correspondently, the conjugated AuCSs hydrodynamic size peaks at 240.4 ± 3.8 nm with mAbs concentration at 1253 μg/ml. For qualitative LF, AuNPs and AuCSs propose the equivalent capability in foretelling the existence of CysC. For quantitative purposes, AuCSs with fainter test lines would enable a wider CysC detection range.

In this work, we present the experimental investigations on a new SPR (Surface Plasmon Resonnace) sensor based on the switch measurement method. The sensor is realized with a deep metallic grating in our case coated with a Pd layer known for its sensitivity to hydrogen1 where the 0th and -1st orders crossed each other at a specific incident angular beam. By achieving a normalized difference between these two orders at this specific working point, any change in dielectric permittivity can be measured when hydrogen interacts with the Pd layer. The sensor developed in this study exhibits promising performance for hydrogen detection and provides proof of concept for the switch measurement method.

Measurement of gas concentration and temperature distribution at high repetition rates in a plasma chemical reactor is important for the optimization of the reactor performance, for example, by placing more catalysts in the reaction zones. Tunable diode laser absorption spectroscopy combined with focal planar arrays is an effective method used for fast mapping of concentration and temperature in gaseous flows. A custom two dimensional (2D) high temperature gas flow cell has been constructed for the validation of the concept. An interband cascade laser and a focal planar array camera (Infratec ImageIR 5355) is employed for detection; 2D beam expanding optics to image the flow cell. The technique will be further developed for calibration and measurement of temperature and concentration, improvement of the speed etc., towards the realization of fast concentration and temperature measurements in a plasma reactor, targeting key plasma catalytic reactions such as methane valorization involving conversion of greenhouse gases such as methane to useful industrial precursors.

Plasmon-enhanced colorimetric histology was recently introduced as a method for visualizing variations in the local refractive index of cells and tissues via a Surface Plasmon Resonance (SPR) induced colour variation. Here we investigate the combination of a Deep Eutectic Solvent (DES) and colorimetric histology as a promising alternative to conventional histological stains. This approach is used to enhance the optical contrast for ultrafine tissue sections whose thickness is below the optical diffraction limit. Traditional histological stains can have limitations, particularly when visualizing ultrafine sections, in terms of specificity and sensitivity. This research explores the potential of DESs to overcome these limitations and yield a massive enhancement of the contrast of histological specimens in the presence of planar plasmonic devices. This novel approach is used to visualize resin embedded cells cut into sections of 120 nm thickness using ultramicrotomy. The DES interaction with the plasmonically active substrates has a significant impact on the measured colorimetric signals which lays the foundation for a promising avenue in the field of histopathology with potential implications for diagnostic medicine and biomedical research.

LSPR sensing applications benefit from well-crafted nanostructures. Current methods, using RTA on a thin metal film, result in random distribution and size variation. We introduce SF₆ plasma surface treatment with ICP-RIE before Au deposition, altering surface affinity to improve gold nanostructure formation. Contact angle measurement verified treatment effectiveness. AFM and SEM examined the nanostructure after fabrication. The absorption spectrum comparison confirmed plasma-treated substrates exhibited enhanced absorptive characteristics for LSPR sensing.

We present a new design of an invisibility cloak, built of two rings of transparent holograms. The proposed device is based on the principle of an Abyss Cloak, which shifts the image of the cloaked object to the exterior position. Our device operates for a visible light and for all azimuthal positions around the device. Preliminary numerical simulations suggest extremely simple material properties for the included holograms, which makes our device very likely to be realised experimentally. To the best of our knowledge, our work presents the first invisibility cloak, operating in a visible range of light and for a wide range of viewing directions, and thus makes a significant contribution to the arsenal of transformation optics devices.

Laser 3D nanolithography enables the fabrication of complex shape micro-optical elements. The freedom of multi-surface designs of such components has cost them to suffer from reflection losses. This work presents the deposition of an Antireflective (AR) coating, using Atomic Layer Deposition (ALD), on hybrid organic-inorganic polymer SZ2080™ microstructures and micro-lenses fabricated using Laser Direct Writing (LDW). The single-wavelength AR coating produced using ALD successfully reduced reflection from 3.3 % to 0.1 % at 633 nm for one surface of SZ2080™.

The mid-infrared birefringence coefficients, including photoelastic coefficients, phase delay, and fast axis angle, are important indicators for evaluating infrared crystal materials. These coefficients can detect deviations introduced during optical glass processing and stress birefringence generated under external forces, which are mostly used to measure the influence of birefringence deviation of optical window under atmospheric pressure before assembly. This paper introduces a dual photoelastic modulators (PEMs) system for detecting birefringence in the near infrared to midinfrared range. The hardware of this system includes a 3390nm laser, a -45°polarizer, a 0°PEM, a +45°PEM, a 90°polarizer, a photodetector, a lock-in amplifier with filter circuit module, and a host computer, which can achieve modulation and demodulation of the polarization state of light and extraction of weak electric signal. The software interface of this system includes, data acquisition card channel setting interface, electrical signal waveform display interface and birefringence coefficient data processing interface. The polarization state analysis method using Stokes parameters and Mueller matrices, along with data processing techniques, enables automated and precise measurement of mid-infrared birefringence coefficients in crystals. Multiple sets of measurement data yield a phase delay of 9.863541 nm for a 15mm thick Si crystal and a phase delay of 8.971042 nm for a 12mm thick ZnS crystal. The repeatability of the measurement device is 0.020, and the measurement uncertainty is 0.019. This system can be extended for precision measurement of stress birefringence in multi-wavelength infrared crystals. It not only fills the gap in testing equipment for mid-infrared crystal photoelastic coefficients but also provides valuable guidance for the design, evaluation, and application of crystal stress birefringence systems.

Laser-Induced Periodic Surface Structures (LIPSS) can be produced using ultra-short (fs) pulsed lasers. The typical Gaussian profile of a single mode ultrafast fiber laser is not ideal, as the fluence across a spot varies. Laser beam shaping can reform the output spot into a square or rectangular shape with a flat-top profile, tailored to the fluence requirements of the application. We present initial results, surface nanotexturing of stainless steel at a rate of 6.8 cm² s ^-1 and efficiency of 0.38 cm² s ⁻¹ W⁻¹ with a 20 W average power laser. Further optimisation will allow the full output power range of the laser to be used to maximise throughput and efficiency. Beam shaping also provides improvements to black marking throughput, where the typical processing speed with a Gaussian spot is less than 0.04 cm² s ⁻¹ while shaped beam increases the productivity up to 0.44 cm² s ⁻¹ .

The essence of resistance spot welding of Cu and Ag terminals is a process that taking copper strip as substrate, silver as solder, under the action of electrode pressure and current, the metal atoms on the welding surface move violently to form a bonding structure. Although the surface quality of solder joints can be characterized by microscopic morphology, the growth of microstructure can also indicate the formation process of welding structure, studying from the view of molecular of welded components can better uncover the essence of welding. In order to accurately evaluate the welding quality of terminals, the movement of molecules of the surface of welding is simulated by calculating the different coordinates of molecules at different times based on molecular dynamics, and the molecular bonding in the system is visually displayed. The molecular dynamics simulation of Cu -Ag is to first determine the initial positions of all atoms in the system, under the constraints of Classical mechanics and ignoring the influence factors other than the atomic nucleus, the real-time positions of each atom are calculated after the next time step, and then iterate in turn until the end of the simulation, to obtain the atomic motion trajectory. Through MD simulation method, the movement process and combination morphology of Cu and Ag atoms in the spot-welding process are visually observed. Different Initial conditions are set to obtain the desired structures and analyze and get the most ideal process parameters. Through molecular dynamics theory analysis, the movement mechanism of atoms in the copper silver welding process is understood. Conduct molecular dynamics simulations of the copper silver atomic system under different conditions and explore the process steps for obtaining the most ideal structure of the copper silver atomic system as in three stages.

As the photoelectric conversion material, semiconductor photocathode plays an important role in the development of vacuum photodetectors and electron sources, and the efficiency and stability of electron emission have always been the focus in photocathode applications. Photocathode is based on the external photoelectric effect. Different from the internal photoelectric effect, photoelectrons generated by light excitation inside the cathode must overcome the surface barrier to escape into the vacuum, so the level of the photoemission ability is closely related to the surface properties. The preparation process usually includes surface cleaning and activation, wherein the activation process under the ultrahigh vacuum condition is regarded as an irreversible and evolutionary process over time. How to characterize the cathode surface in situ is particularly important for understanding the mechanism of photoemission generation and degradation. Nowadays, the surface characterization methods including photoelectron spectroscopy, synchrotron x-ray characterization, electron diffraction, scanning probe microscopy, spectral response measurement, and photoreflectance spectroscopy are utilized as assisted evaluation tools to prepare photocathodes. Here, we present a newly developed integrated ultrahigh vacuum facility for photocathode preparation and in-situ characterization. With this system, the surface cleaning, activation and degradation processes for semiconductor photocathodes were effectively characterized by photoelectron spectroscopy and spectral measurement. The integrated photocathode preparation and characterization system can realize in-situ multi-information characterization in ultra-high vacuum environment, and the element composition and chemical state analysis of the specified region can be realized by using X-ray secondary electron image and micro-area analysis function, which is helpful to optimize the preparation process of photocathodes.

Azopolymers are unique materials with interesting optical properties due to the photoisomerization reaction, which induces large material motions at molecular, nanometrical and even microscopically scales. Several applications in different fields, in particular in photonics and biocompatible materials, have exploited the fabrication of Surface Relief Gratings (SRG) by means the photo-form of azopolymers thin films. The phenomena from which has origin of the surface relief formation is still a matter of discussion and far away from a complete understanding. Consequently, the implementation of new characterization modalities could help to achieve the comprehension of this fundamental issue. So far, different methods as direct efficiency diffraction or Atomic Force Microscopy have been adopted to study the physical properties of such gratings structures as well to characterize the material. Nevertheless, for different reasons those techniques have inherent drawbacks. In this work, we report the results obtained by adopting a full-field interferometric method (in Digital Holographic modality) for monitoring in-situ, quasi-real time and with high spatial resolution the writing process of azopolymer structures on thin films. The micro-size patterns of SRG were fabricated by an interference lithography technique (i.e. Lloyd’s mirror). The proposed method is an interesting diagnostic tool that could be useful for investigating the yet unclear origin and related mechanism of SRGs formation and their dynamic evolution.

Immobilized photocatalysis, using economical UV-A LEDs and light activated metallic nanomaterials, may provide a sustainable, reusable at-source hospital wastewater treatment solution for the oxidation and elimination of toxic hospital drugs. At bench-scale, high-temperature calcination of photocatalysts onto spherical supports, such as glass beads, is mostly used to incorporate photocatalysts onto solid (porous) structures. However, the use of spherical support materials in fast-flowing hospital wastewater can cause unwanted hydrodynamic effects. In this study, planar borosilicate support materials were covalently functionalized with an effective photocatalytic nanomaterial thin-film and tested in a novel UV-light fixed-bed reactor. This project aims to demonstrate proof-of-principle of immobilized photocatalysis to oxidize and eliminate various ecotoxic and persistent drugs in fast-flowing hospital wastewater.

In the current study, we report the all-inorganic lead-free halide perovskites-oxide heterojunction based optoelectronic device fabrications on Si substrate by employing cost-effective chemical bath deposition (CBD) and hot-injection techniques. The selective rare-earth doping of erbium (Er) in ZnO nanowires is performed by employing double-step CBD technique on Si platform for developing a superior heterojunction between Er:ZnO and Si. Furthermore, lead-free perovskites NCs of CsSnCl3 are synthesized by using cost-effective hot-injection method and such NCs are decorated over the Er:ZnO nanowires to passivate the surface defect states. The effect of Er-doping and CsSnCl3 incorporation on structural, optical and luminescence properties of nanowire heterojunctions has been successfully investigated by employing XRD, UV-VIS and PL. The crystal structure of Er:ZnO and Er: ZnO-CsSnCl₃ heterojunctions has been analyzed using X-Ray Diffraction (XRD) technique, which confirms the polycrystalline nature of nanowires with the formation of a highly crystalline cubic phase of CsSnCl₃. The optical absorption of Er:ZnO nanowires and CsSnCl₃ NCs are studied by using ultraviolet-visible (UV-VIS) spectroscopy and corresponding energy bandgaps are estimated to be 3.31 eV and 3.24 eV, respectively. The oxygen vacancies and complex defect states are minimized in ZnO nanowires by Er-doping and perovskites NCs addition and such CsSnCl3 decorated Er:ZnO nanowires exhibit enhanced UV luminescence as compared to undoped ZnO. Finally, photoresponse of undoped, Er-doped and CsSnCl₃ incorporated ZnO nanowires/Si heterojunction has been studied by measuring dark and photo-current and photo-current switching at UV-A wavelength region and such heterojunctions shows excellent photoresponse under self-powered mode. Therefore, such perovskites incorporated Er:ZnO nanowires/Si heterojunction can be a potential candidate for fabricating a highly responsive self-powered UV-detector (UV-A).

In the last decade, lead perovskites have shown a remarkable performance in photovoltaic applications, but they are vulnerable to stability problems. Therefore, in order to obtain lead-free materials that could successfully replace the single perovskites, we have experimentally realized methylammonium (MA) based double perovskite (MA)₂NaBiCl₆ for the very first time by the single-step method of hydrothermal which could be a potential analog of lead-based single perovskite for various semiconducting applications. We have investigated the structural characteristics of ((MA)₂NaBiCl₆ from X-Ray Diffraction (XRD) measurement. The observed diffraction peaks confirm the phase formation of the (MA)₂NaBiCl₆ and are in accordance with the reference data. To look into the optical behavior of (MA)₂NaBiCl₆, we have done a room temperature Photoluminescence (PL) spectroscopy experiment and observed a broad PL peak at 480 eV corresponding to an optical band gap of 2.58 eV attributed to the phenomena of phonon-assisted carrier recombination and band-to-band transition in the synthesized material. Moreover, an excellent absorbance peak has been seen from the ultraviolet-visible (UV-vis) spectroscopy plot. Furthermore, a direct and indirect bandgap of 2.25 eV and 2.01 eV respectively has been observed from the Tauc plot extracted using UV-vis data. Also, we have observed a good transmittance behavior from Fourier Transform Infrared (FTIR) spectroscopy plot. The Scanning Electron Microscopy (SEM) images were observed for (MA)₂NaBiCl₆ which indicate the presence of a uniform nanorod-like structure. This novel finding provides a stable and greener alternative for lead halide-based single perovskite to the research and scientific community for numerous semiconducting applications.