Holographic laser ablation for nanopatterning

Current lithography methods to produce nanophotonic devices for optical applications are costly and time consuming. Holographic direct laser interference patterning has helped to establish a strategy to rapidly create 1/2D nanopatterns from a variety of materials. A 640 nm × 640 nm pattern structure of Au-Ti was accomplished by controlling the distances between the laser source, the recording medium, and the object. This metal structure has a limitation in regard to thickness to develop better and efficient light diffraction intensity. Later, the Denisyuk reflection mode method was used on the films (about 1 µm) of four ink-based dye colours (black, red, blue, and brown) to fabricate low-cost and efficient nanopatterns. The dyes have the same structural nano spacing (840 nm), but they produced different diffraction in response to monochromatic and broadband light. The recording mediums have different light absorption ranges and the black has the highest absorption. After that, we focused on contact lenses which are universal low-cost biomedical devices with possible applications as quantitative analytical devices for point-of-care diagnostics. Incorporating nanoscale features into commercial contact lenses as low-cost biosensors is considered a challenge. As the black dye has a high optical absorption, it was deposited over a contact lens to produce optical nanostructures on the surface, via holographic laser ablation for sensing ocular diseases. The holographic nanostructures showed a great response to sensing a change of Na+ ions (±47 mmol L-1) in a human tear, to diagnose the severity of a dry eye condition at the early stages. Likewise, this advantage of the black dye’s absorption can be used to produce economical optical strain sensors for civil engineering, aerospace and human interface applications. A holographic interference patterning mode was used to produce nanostructures on a commercial adhesive tape to fabricate a surface compatible, lightweight and cost effective strain sensor for rapid response to cracks, deflections or tears of 5 µɛ

Laser Nanopatterning of Colored Ink Thin Films for Photonic Devices

Nanofabrication through conventional methods such as electron beam writing and photolithography is time-consuming, high cost, complex, and limited in terms of the materials which can be processed. Here, we present the development of a nanosecond Nd:YAG laser (532 nm, 220 mJ) in holographic Denisyuk reflection mode method for creating ablative nanopatterns from thin films of four ink colors (black, red, blue, and brown). We establish the use of ink as a recording medium in different colors and absorption ranges to rapidly produce optical nanostructures in 1D geometries. The gratings produced with four different types of ink had the same periodicity (840 nm); however, they produce distant wavelength dependent diffraction responses to monochromatic and broadband light. The nanostructures of gratings consisting of blue and red inks displayed high diffraction efficiency of certain wavelengths while the black and brown ink based gratings diffracted broadband light. These gratings have high potential to be used as low-cost photonic structures in wavelength-dependent optical filters. We anticipate that the rapid production of gratings based on different ink formulations can enable optics applications such as holographic displays in data storage, light trapping, security systems, and sensors

Holographic Writing of Ink-Based Phase Conjugate Nanostructures via Laser Ablation

Abstract The optical phase conjugation (OPC) through photonic nanostructures in coherent optics involves the utilization of a nonlinear optical mechanism through real-time processing of electromagnetic fields. Their applications include spectroscopy, optical tomography, wavefront sensing, and imaging. The development of functional and personalized holographic devices in the visible and near-infrared spectrum can be improved by introducing cost-effective, rapid, and high-throughput fabrication techniques and low-cost recording media. Here, we develop flat and thin phase-conjugate nanostructures on low-cost ink coated glass substrates through a facile and flexible single pulsed nanosecond laser based reflection holography and a cornercube retroreflector (CCR). Fabricated one/two-dimensional (1D/2D) nanostructures exhibited far-field phase-conjugated patterns through wavefront reconstruction by means of diffraction. The optical phase conjugation property had correlation with the laser light (energy) and structural parameters (width, height and exposure angle) variation. The phase conjugated diffraction property from the recorded nanostructures was verified through spectral measurements, far-field diffraction experiments, and thermal imaging. Furthermore, a comparison between the conventional and phase-conjugated nanostructures showed two-fold increase in diffracted light intensity under monochromatic light illumination. It is anticipated that low-cost ink based holographic phase-conjugate nanostructures may have applications in flexible and printable displays, polarization-selective flat waveplates, and adaptive diffraction optics

Conformable Holographic Photonic Ink Sensors Based on Adhesive Tapes for Strain Measurements

Buildings, bridges, and aircrafts are frequently exposed to fluctuation loads, which could start with a fine crack that instantly leads to unpredictable structure failures. The stationary strain sensors can be utilized, but they are costly and only detect limited deformation forms and sizes. Here, we fabricated photonic strain sensors on adhesive tapes, which can provide real-time monitoring of irregular surfaces. Holographic interference patterning was used to produce nonlinear curved nanostructures of one dimensional (1D) (900 nm × 880 nm) and two dimensional (2D) from a black dye film on a robust uniform adhesive layer and heat resistance tape. The patterned structure of the black dye was stable in broad pH environments. Diffracted light from the curved nanostructure detected the signal during structural damage, a shift or material tear of 5 μϵ at less than 1.3 N cm -2. Additionally, the 2D nanostructure detected a surface change from x or y axis. Tilting the 1D structure within a range of 0.3° to 14.2° provided visible wavelength changes under broadband light to reveal early deflection signs. The curved nanopatterns could be also used for transferable holographic symbol design. Photonic nanopatterns on an adhesive tape could be used as a rapid response, conformable, lightweight, and low-cost dynamic strain sensor

Laser Nanopatterning of Colored Ink Thin Films for Photonic Devices

Nanofabrication through conventional methods such as electron beam writing and photolithography is time-consuming, high cost, complex, and limited in terms of the materials which can be processed. Here, we present the development of a nanosecond Nd:YAG laser (532 nm, 220 mJ) in holographic Denisyuk reflection mode method for creating ablative nanopatterns from thin films of four ink colors (black, red, blue, and brown). We establish the use of ink as a recording medium in different colors and absorption ranges to rapidly produce optical nanostructures in 1D geometries. The gratings produced with four different types of ink had the same periodicity (840 nm); however, they produce distant wavelength dependent diffraction responses to monochromatic and broadband light. The nanostructures of gratings consisting of blue and red inks displayed high diffraction efficiency of certain wavelengths while the black and brown ink based gratings diffracted broadband light. These gratings have high potential to be used as low-cost photonic structures in wavelength-dependent optical filters. We anticipate that the rapid production of gratings based on different ink formulations can enable optics applications such as holographic displays in data storage, light trapping, security systems, and sensors

Optical Fiber Sensors: Working Principle, Applications, and Limitations

Fiber‐optic technology emerged originally for applications in data transmission and telecommunications. However, sensors based on fiber‐optics have been developed rapidly because of their excellent sensing performances and capability to function in remote and harsh environments. The usage of fiber‐optic sensors has flourished in many fields over the past 30 years due to the fiber‐optic's inherent advantages: cost‐effectiveness, miniaturized size, light weight, and immunity to electromagnetic interference. This work reviews the fiber‐optic sensors based on Bragg gratings, long period gratings, interferometers, surface plasmon resonance, fluorescence, and light diffusion. Brief theory of sensing principle, fabrication method, applications, advantages and disadvantages of the different fiber‐optic sensors, are addressed. Recent progress in numerous sensing fields, including environmental, industrial, and biomedical are discussed for each class of fiber‐optic sensors. The review highlights the methods and techniques used to overcome the sensing challenges. Finally, prospect of future developments of fiber‐optic sensors is summarized

SARS-CoV-2 vaccination modelling for safe surgery to save lives: data from an international prospective cohort study

Background: Preoperative SARS-CoV-2 vaccination could support safer elective surgery. Vaccine numbers are limited so this study aimed to inform their prioritization by modelling. Methods: The primary outcome was the number needed to vaccinate (NNV) to prevent one COVID-19-related death in 1 year. NNVs were based on postoperative SARS-CoV-2 rates and mortality in an international cohort study (surgical patients), and community SARS-CoV-2 incidence and case fatality data (general population). NNV estimates were stratified by age (18-49, 50-69, 70 or more years) and type of surgery. Best- and worst-case scenarios were used to describe uncertainty. Results: NNVs were more favourable in surgical patients than the general population. The most favourable NNVs were in patients aged 70 years or more needing cancer surgery (351; best case 196, worst case 816) or non-cancer surgery (733; best case 407, worst case 1664). Both exceeded the NNV in the general population (1840; best case 1196, worst case 3066). NNVs for surgical patients remained favourable at a range of SARS-CoV-2 incidence rates in sensitivity analysis modelling. Globally, prioritizing preoperative vaccination of patients needing elective surgery ahead of the general population could prevent an additional 58 687 (best case 115 007, worst case 20 177) COVID-19-related deaths in 1 year. Conclusion: As global roll out of SARS-CoV-2 vaccination proceeds, patients needing elective surgery should be prioritized ahead of the general population