This study has demonstrated a combination of single-point diamond turning (SPDT) and solid-state diffusion bonding (SSDB) to achieve low-pressure joining of Cu plates. SPDT on the faying surfaces has resulted in nano-level surface roughness of Sa 1.56 nm and Ra 1.32 nm. Diffusion bonding experiments were performed by varying bonding temperatures from 600 degrees C to 800 degrees C and at a low bonding pressure of 4 MPa. It was interesting to note that a low-temperature bonding at 600 degrees C has resulted in a bonding ratio of 92.2 %, and it significantly enhanced to 98.4 % at 800 degrees C. Complete grain boundary migration was observed along the joint interface for the sample bonded at 800 degrees C. The shear load for joint failure increased from 13.06 kN to 18.36 kN with an increase in bonding temperature, which was correlated with the microstructural observation. The fractography study indicated a ductile mode of failure. Low-pressure diffusion bonding of the Cu plate with integrated channels was successfully demonstrated without deforming the channels. Precision alignment of the arrayed channels for conformal cooling applications could be achieved using a combination of SPDT and SSDB, which would be challenging with other joining techniques.

The stitching of subaperture wavefront profiles is a prominent technique for freeform and large size optical wavefront metrology. The measurements of wavefront in small areas with suitable techniques are carried out and for stitching those wavefronts, the stitching coefficients are determined by error minimization using least square method. In this work an alternative approach for optimization of the stitching coefficients are investigated using genetic algorithms (GA). For the study, two types of measurement data viz. interferometric measurement of subaperture profiles of the plane wavefront and scanning Shack Hartmann sensor (SHS) based subaperture profiles measurement of freeform wavefronts are used. The stitched profile for plane wavefront using GA technique is 41.73 wave (peak to valley) [ 1 wave = 632.8 nm], which exactly matched with the nominal value of plane wavefront profile without any error. For freeform wavefront subaperture stitching, the residual error has been decrease to 0.19 wave as compared to 4.2 wave in case of the least square minimization stitching technique. The results are encouraging and the technique has potential to be used for stitching of the subaperture measurements.

The integration of reconfigurable intelligent surfaces (RIS) into the receiver section of indoor visible light communication (VLC) systems is still in its early stages. Although amplification in the optical domain is achievable using liquid crystal (LC)-based RIS, the lack of a precise and adaptable channel model hinders its effective design and application. In this study, we demonstrate how a liquid crystal-based RIS can be integrated with the receiving unit of an indoor VLC system and highlighted its role as an optical amplifier controlled by external voltage. We also identified the shortcomings of the existing VLC channel model with tunable LC receivers and proposed a robust analytical framework to more accurately estimate signal strength. Furthermore, the impact of external tuning voltage on the transmission coefficient and amplification gain factor of the LC cell is analyzed in detail.

Hybrid optical surfaces are gaining attention for system miniaturization and enhanced optical throughput, but challenges arise in creating precise tool paths for dual profiles with consistent micro-grooves and minimal form errors. In this study, an innovative retract toolpath approach is reported to fabricate hybrid surfaces with high-quality finish using the 2-axis configuration of a diamond turning machine. A hybrid surface with a 5 mu m feature size on a 38 mm radius spherical profile was fabricated using a 6.35 mu m nose radius diamond tool, with 1000 rpm spindle speed, 0.1 mm/min feed rate and 2 mu m depth of cut. The retract toolpath approach offers better control over feature size, pitch and groove depth in microstructures than the continuous method. The proposed approach, validated on aluminum, brass and PMMA, demonstrated form errors below 0.63 mu m and surface roughness under 4.5 nm. The results show that the proposed tool path approach is suitable for maintaining precise microstructuring over curved surfaces and for different materials to cater to the needs of wide application fields. Specifically, for compact systems in widespread visible and near infrared applications, which require precise and miniaturized optical components to enhance the field of view and resolution of the systems.

This study introduces a novel approach to design and enhance the diffraction efficiency of polarizationindependent multilayer dielectric gratings, which are utilized for spectral beam combining in off-Littrow configurations. The key challenges associated with using polarization-independent multilayer dielectric gratings in off-Littrow setups are addressed, with the modal method employed to highlight the necessity of tapering grating structures during optimization. The design process involves the selection of optimal grating parameters and incidence angles for individual lasers in spectral beam combining. The rigorous coupled-wave analysis combined with particle swarm optimization is used to compare the average diffraction efficiency of three different types of polarization-independent multilayer dielectric grating designs, optimized in both Littrow and off-Littrow configurations. The proposed design achieves 97.85% average diffraction efficiency, with a minimized grating aspect ratio of 1.65, making it highly suitable for spectral beam combining applications. Furthermore, tolerance analysis of the gratings summarized that the proposed design exhibits the highest tolerance range among the evaluated configurations, ensuring robustness against fabrication-related deviations.

Infrared (IR) materials like single-crystal germanium (sc-Ge) are gaining attention due to their outstanding optical properties, especially in infrared (IR) applications. This study focuses on improving the surface finish of sc-Ge substrates for IR applications using a diamond turning machine (DTM). The challenges in achieving the desired surface quality are addressed through an innovative approach that combines the response surface methodology (RSM) with a teaching-learning-based optimization (TLBO) algorithm. The optimal surface quality is achieved at lower depths of cut and feed rates, along with moderate spindle speeds, resulting in smoother topography and lower surface roughness. Statistical modeling using RSM highlights TLBO's efficacy over traditional optimization methods, achieving a 0.37 nm surface roughness (Sa) under optimised machining parameters. Experimental validation demonstrate a close agreement between the optimized and experimental values, with a deviation of 3.24%. This study provides practical insights for efficient use of DTM to enhance performance of sc-Ge optical components for IR applications, contributing to surface quality optimization in the field of ultra-precision optics fabrication.

In the present era, a significant amount of research work is focused on eco-friendly technologies and advanced liquid waste management strategies. Notably, industries primarily textile chemical processing sectors which are inherently involved with a wide array of dye usage, are integral focal points for these transformative endeavors. Against this backdrop, we have successfully synthesized an innovative photocatalyst with a remarkable capability to rapidly neutralize deleterious dyes within an astonishingly brief span of 4-6 minutes, facilitated by exposure to UV-visible irradiation. Briefly, our approach entails the hydrothermal synthesis of a composite material based on zinc stannate (ZnSnO3) nanoparticles integrated with the copper-decorated metal-organic framework (ZnSnO3@H3BTC-Cu MOF). The resulting material is endowed with a crystalline and porous architecture that confers a specific surface area measuring 437.25 m2 g(-1), a value surpassing that of unadorned nano-ZnSnO3 by a factor of approximately 15 (29.11 m2 g(-1)). Noteworthy beyond its enhanced surface features, the newly synthesized ZnSnO3@H3BTC-Cu MOF exhibits remarkable antibacterial efficacy against gram-positive S. aureus and gram-negative E. coli bacterial strains. It might also be considered a stable photocatalyst to be used in wastewater treatment, as evidenced by the photoelectrochemical and photocatalytic investigation.

This chapter provides a comprehensive review of the design, fabrication, and metrology aspects of freeform optics, shedding light on the latest advancements in this rapidly evolving field. With a focus on innovative techniques and emerging technologies, it delves into the intricate world of designing complex optical surfaces that deviate from traditional spherical and aspherical forms. The fabrication methods for freeform optics, including precision machining, polishing and molding, are discussed, highlighting their advantages and challenges. Furthermore, the chapter discusses the critical role of metrology in ensuring the accuracy and quality of freeform optical components. It serves as a useful resource for researchers, engineers, and scientists seeking a deep understanding of freeform optics.

We report the effect of integrating metasurface-aided reconfigurable intelligent surfaces (RISs) on the signal-tointerference-plus-noise ratio (SINR) and data rate of a multi-cell visible light communication (VLC) system. RIS has been deployed in the channel between transmitter and receiver to redirect the reflected light in the desired directions, even in the absence of line-of-sight (LoS) links. Results show that the introduction of RIS has improved average SINR but reduced average illumination level compared to a no-RIS system. As the quantity of RIS increases, a discernible improvement in the maximum SINR value is observed. Here, three different receiver geometries, namely, a photodiode (PD), freeform diversity receiver (FDR), and modified FDR (MFDR), have been adopted. The impact of individual receivers has been reported in the presence of light path blockage. MFDR geometry is found to be most suitable with more coverage probability compared to the other two receivers. With (40 cm x 24 cm) RIS area, during blockage, MFDR maintains an average SINR of 21.95 dB, which is 97.29% and 14.24% greater than PD and FDR, respectively. (c) 2024 Optica Publishing Group

The several advantages of visible light communication (VLC) have made it a potentially competent candidate for future communication technology. The reliability of the VLC system depends on the line-of-sight (LOS) links. However, surrounding environments pose unique challenges, frequently causing LOS blockages. The reconfigurable intelligent surfaces (RIS) also known as intelligent reflecting surfaces (IRS) is a collection of tunable passive elements that have proven their ability in RF communication to manipulate and control the transmitted/reflected RF signals by changing the orientation or phases of RIS. RIS is anticipated to play a crucial role in enhancing VLC by shadowing compensation, extending coverage by controlling the beam directions and improving communication reliability by mitigating interferences. This work delves into the emerging field of reconfigurable intelligent surfaces (RIS) and their transformative role in multi-cell indoor visible light communication (VLC) systems. A RIS-based indoor multi-cell system model is developed for the purpose of mitigating inter-channel interference (ICI) issues during LOS blockages. The SINR performance of the proposed system is estimated for four different scenarios. Results show that the integration of RIS in between VLC channels can enhance the detector’s received power up to 27 times compared to the power received from the LOS and NLOS channels. Moreover, incorporating RIS has raised the average SINR value by 25% during no blockage and more than 70.4% during the blockage.

This study focuses on addressing the growing concern of electromagnetic interference (EMI) pollution caused by the widespread use of electronic devices. An effective shielding material using barium hexaferrite nanoparticles {BaFe12O19 (BaM) NHFs} and its nanocomposite (NC) with polyaniline (PANI) applied to cotton fabric was developed. The BaM NHFs and BaM/PANI NCs were synthesized by using modified sol-gel and self-assembly coating methods. The hexagonal structure of BaM NHFs was confirmed through powder X-ray diffraction (pXRD) analysis. High-resolution electron microscopy was utilized to study the morphology of BaM/PANI NCs. The ferromagnetic properties of the prepared samples were investigated by using alternating gradient magnetometry. The BaM NHFs and BaM/PANI NCs were treated with the cotton fabric using the pad-dry-cure method with low loading percentages of 0.1 and 1% add-on to the fabric's weight. The treated fabrics were then evaluated for their EMI shielding behavior. Remarkably, the fabric treated with BaM/PANI NCs demonstrated excellent EMI shielding effectiveness in the X-band frequency region, even at a lower concentration of 1% compared with pure PANI and BaM NHFs. This suggests that further increasing the loading percentage of BaM/PANI NCs on cotton fabric could significantly enhance the shielding performance for various important applications.

Optical instruments such as X-ray optics, high-power laser systems, synchrotron beamlines, lithography, and laser-based sensors, require a superfine optical surface to meet their tight optical performance tolerances. This study describes the development of a nanocomposite-based nanoabrasive that can provide a superfinish optical surface via optical polishing. The Malic acid as an organic surface modifier is functionalized with the superparamagnetic iron oxide nanoparticles (SPION). Strong chemical attachment between SPION nanoparticles and the Malic acid is verified through fourier transform infrared spectroscopy. A significant enhancement in the surface area and zeta potential value of SPION nanoparticles is observed when it is functionalized with the Malic Acid. The particle size distribution of the functionalized nanoabrasive is also narrowed down to 8-26 nm. The polishing performance of the functionalized SPION nanoabrasive has been investigated on the BK7 and Fused Silica glasses for precision optical polishing. The polishing results showed superfine surface finishing of the BK7 glass and the Fused silica glass down to the Ra value of 0.23 nm and 0.1 nm, respectively.

The manufacturing and characterization of freeform optical surfaces are influenced by their high sensitivity to misalignments. In this work, the computational sampling moiré technique combined with phase extraction is developed for the precise alignment of freeform optics during fabrication and in metrology applications. This novel, to the best of our knowledge, technique achieves near-interferometry-level precision in a simple and compact configuration. This robust technology can be applied to industrial manufacturing platforms (such as diamond turning machines, lithography, and other micro-nano-machining techniques) as well as their metrology equipment. In a demonstration of computational data processing and precision alignment using this method, iterative manufacturing of freeform optical surfaces with a final-form accuracy of about 180 nm was accomplished.

Efficacy and the outcome of the magnetorheological finishing (MRF) related processes depends on two crucial factors, (i) a finishing abrasive and (ii) a magnetic particle. However, the magnetic particles although necessary, become a hindrance for non-magnetic abrasive particles in directly reaching the surface to be finished. This study relates to the development of SPION-based smart material for MRF and all their variant processes. The SPION particles possess dual nature such as nanoabrasives and magnetic nanoparticle. The superparamagnetic property of the developed SPION particle has been confirmed by alternating gradient magnetometer with the saturation magnetization value of 82.23 emu/g. The polishing performance of the developed SPION-based particle as abrasive has been investigated on a BK-7 optical glass and the polishing is done via a 5-axes automated ball end magnetorheological finishing (BEMRF). The developed SPION abrasive enhanced the finishing process of the BEMRF technique and provided surface finishing on the BK-7 substrate up to the surface roughness (Ra) values of 22.3 nm with the Ra improvement of 88.14%.

This paper presents an experimental investigation on ultrasonic vibration–assisted magnetorheological finishing (VAMRF) process for improved material removal rate (MRR) and surface finishing on glass optics polishing. An additional process parameter, i.e., vibrating motion, is added in the magnetorheological finishing (MRF) process for corrective polishing of glass optics. Influence function, a material removal characteristic of the process and necessary for deterministic processing, was calculated experimentally for the VAMRF. The results show that hybrid VAMRF provides approximately 20

A Li-Fi receiver front-end is proposed using monolithic-freeform-Fresnel profile. The modified design replaces four orthogonally oriented optical front-end into a single unit and exhibits 81 dB average SINR with more than 25% reduction in dimension.

The paper presents a slope based wavefront sensor for testing of phakic Intraocular lenses (pIOLs). A Shack-Hartmann wavefront sensor is used to measure the performance parameters in order to optimise the pIOLs. Both the simulation and experimental results have been presented.

The prospect of utilizing freeform optics to develop a more compact and smaller VLC receiver front-end is explored in this study for a multi-cell indoor environment. A novel freeform surface element (FSE) has been fabricated by an ultra-precision single-point diamond turning (SPDT) machine and characterized by the mechanical and optical profiler to investigate its potential use inside a freeform diversity receiver. A 9 dB increment in average signal-to-interference-plus -noise-ratio (SINR) is observed after third iteration while the form error reduces to 1.92 mu m. The communication functionality of the fabricated FSE is also validated experimentally. The average SINR over the communication floor is computed as 109.29 dB. The fabricated freeform element is further modified to a freeform Fresnel profile for more compactness. The result shows, a substantial decrease in receiver height (2.314 mm) is possible using the proposed approach. Moreover, different fabrication challenges related with freeform Fresnel have been identified and discussed to set the future research pathway.