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A target-type fiber optic velocity sensor is presented based on panda fiber attached to aluminum-cantilever, and experimentally demonstrated high sensitivity and precision measurement of seawater velocity. In this paper, the velocity sensitivity formula of the sensor is derived first, and the effective elastic coefficient (Pe) of Panda fiber is calculated to be 0.988 by finite element algorithm. Secondly, seawater velocity measurement system was established experimentally with circulating flow tank, and experimental results showed that the velocity sensitivity is up to 114.69 nm/(ms^‐1) at 0.31 m/s when the target radius and cantilever thickness are 2.00 cm and 0.20 mm respectively, which proves that highly sensitive velocity measurement is achieved with panda fiber coupled aluminum-cantilever. Comparing the measurement results of the sensor with Acoustic Doppler Velocimetry, the average absolute error and the root mean square error (RMSE) are 0.012 m/s and 0.00249 m/s respectively, which realized high precision measurement of seawater velocity. Therefore, the system has good application in the measurement of seawater velocity due to its advantages of high sensitivity, wide range and simple structure.

The utilization of X-rays produced by interaction between relativistic electrons and laser pulses finds profound application in domains such as photoelectron spectroscopy. Through numerical simulation, the influence of the laser pulse delay time ${\tau }_0$ and the initial Lorentz factor ${\gamma }_0$ on the spatial and spectral properties of radiation produced by electron cross collision with a circularly polarized laser pulse is investigated. Also, the optimal parameters for generating quasi-monochromatic pulses and high-order harmonic radiation are discussed. The results reveal that when $|{\tau }_0|$ is large, the electron collides with the leading or trailing edge of the laser pulse, resulting in superior quasi-monochromatic radiation pulses. However, when ${\tau }_0$=0, the electron collides with the center of the laser pulse, which is most favorable for the generation of high-order harmonics. Furthermore, ${\gamma }_0$ has a negligible impact on the monochromaticity of the fundamental harmonic but plays a detrimental role in forming a single quasi-monochromatic pulse at higher values. Instead, higher ${\gamma }_0$ promotes the broadening of high-order harmonics. These results are important for obtaining radiating X-rays with different properties according to practical requirements.

An analytical solution of the three-dimensional transient temperature distribution for skin tissue when heated by a laser heat source is presented in this work. An equation for the three-dimensional bioheat transfer of skin tissue is obtained firstly, and the transient temperature value at any point inside the skin tissue can be solved using the separation variable method and the Newton-Cotes method. Previous research primarily focused on semi-infinite domains, while this work presents an analytical solution for finite domains. A comparison of present analytical solution with simulation software results and numerical solution is given to demonstrate the feasibility of the analytical solution. The three-dimensional temperature distribution of skin tissue irradiated by a laser is theoretically studied. The extent of thermal damage to skin tissue is assessed by substituting the analytical solution of the temperature field for laser-irradiated skin tissue into the thermal damage equation. The calculations in this work reveal that the variation of temperature field in biological tissues is dependent not only on the laser incident light intensity and the optical parameters of the tissues but also on the heat transfer properties of the biological tissues, such as the blood perfusion rates.

A Thulium/Holmium co-doped fiber laser with high-energy noise-like rectangular pulses at the central wavelength of 1985 nm is experimentally demonstrated. The experimental setup is based on a 298-m long nonlinear optical loop mirror. By varying the pump power from 3 to 10 W, the noise-like rectangular pulse width can be tuned from 2.8 to 15.2 ns, respectively, and under a maximum pump power of 10 W, 1.45 W of average output power is obtained. The pulse repetition rate is 671 kHz. Consequently, highly energetic optical pulses with 2.16 µJ pulse energy and an estimated peak power of 142 W are achieved. To the best of our knowledge, these pulses, which are generated directly from the laser cavity, possess the highest average output power and pulse energy for noise-like pulse emission in the near 2 µm wavelength region. The proposed laser source has the most straightforward all-fiber cavity design that has been proposed for generating high-energy noise-like rectangular pulses, and as such has potential applications in scientific research and as a pump source for mid-infrared supercontinuum generation.

Recent years have witnessed the popularity of wearable devices. These devices use Wireless Body Area Networks (WBANs) for healthcare monitoring, personalized tracking, and various other applications. An important component of these devices is the wearable antenna that provides reliable and efficient wireless communication between body-worn sensors and external devices. This paper presents a novel metasurface-based wearable antenna for WBAN applications. By incorporating metasurfaces into the antenna design, achieving enhanced performance is possible. The design was tested using four flexible substrates: wool, paper, fleece, and felt. The paper substrate was chosen because of its superior performance. The dimensions of the antenna are 30 mm x 20 mm, and a 5 ×3 metasurface is used, whose unit cell comprises a square patch. Simulation and experimental results have been performed to measure the radiation pattern, return loss, and gain. A good corroboration is observed between the measured and simulated results. The antenna resonates at three frequencies and offers wide-band resonance characteristics when backed by the metasurface. The peak gain of the antenna without the metasurface was less than 4 dB, but when backed by the metasurface, the peak gain was enhanced to approximately 6 dB. Also, it has been observed that the designed antenna’s performance is not significantly affected by the radius of curvature, making it ideal for on-body measurements. This design can inspire further research on low-cost paper substrate-based antennas for WBAN applications.

This manuscript introduces highly sensitive surface plasmon resonance (SPR) sensor for early detection of the dengue virus. Through extensive optimization using MATLAB, the sensor architecture is meticulously constructed with a BK7 prism, Copper (Cu) layer, Gallium selenide (GaSe), Tungsten disulphide (WS₂), and a sensing medium (SM) containing blood components (infected platelets and normal platelets) to ensure optimal performance. Use of WS₂ emerges as a highly effective biomolecular recognition element (BRE) layer, leading to exceptional sensor capabilities. The proposed sensor achieves a peak sensitivity (S) of 303.28 (˚/RIU) and a resonance angle shift (∆θ_res.) of 10˚ specifically during the detection of infected platelets. Computational modeling using COMSOL Multiphysics validates the ability of the sensor to generate an intense electric field with a magnitude of 1.68×10⁵ (V/m) and a penetration depth (PD) extending to 153.24 nm in the SM. This unique combination of PD and enhanced performance parameters positions the proposed SPR biosensor as a promising tool for the early-stage detection of the dengue virus.

In this work, we report preparing zinc cobalt oxide/zinc oxide nanocomposite via a facial in situ hydrothermal route. The crystal structure of the as-synthesized products was characterized using X-ray diffraction (XRD). The XRD results confirmed the preparation of a ZnCo₂O₄/ZnO nanocomposite. A field emission scanning electron microscope (FESEM) was used to analyze the morphology of samples. From FESEM images of the nanocomposite, ZnCo₂O₄ nanoparticles have been decorated on ZnO hexagonal nanoplates. The optical properties of the as-prepared samples were characterized by UV–vis and photoluminescence (PL) techniques. Furthermore, we investigated the photocatalytic performance of the obtained samples for acid orange 7 (AO7) dye. It was found that the ZnCo₂O₄/ZnO nanocomposite exhibited appreciable photocatalytic performance under visible light irradiation in comparison with ZnCo₂O₄ and ZnO nanostructures.

This study introduces a highly sensitive temperature sensor based on long-period fiber grating (LPFG). The sensor is composed of a long period fiber grating covered by a higher RI (RI) layer of polyvinyl alcohol (PVA) and a lower RI layer of polydimethylsiloxane (PDMS). The PVA layer enables the sensor to operate in the mode transition region with high sensitivity, and the PDMS layer further enhances the temperature sensitivity owing to its high thermos-optic coefficient. In addition, the sensor can mitigate the influence of humidity due to the hydrophobic properties of PDMS. Experimental results show that the temperature sensitivity can achieve to 1232.3 pm/℃ within the range of 20℃-100℃ for an LPFG with a period of 363 μm coated with a 265 nm PVA layer and a 20 μm PDMS layer.

We propose a method to obtain uniform multilayer coatings using vacuum assemblies with a linear ion source to manufacture narrow-band interference filters essential in astrophysical research for space object imaging in important spectral lines, and to provide multi-channel fiber-optic transmission of information. Interference filters and other optical systems, for example, high-reflective mirrors, steep-front beam splitters contain up to hundreds of film layers deposited onto a substrate. During the coating deposition, film thickness on the substrate must be strictly withstood and be uniform throughout the entire surface. This can be achieved by placing the linear source and target on the same platform and by conducting a test target sputtering on a fixed substrate. There is an inflection line on the coating thickness distribution on the substrate. By moving the platform, the inflection line midpoint is aligned with the center of the rotating working substrate, and in this position, the substrate is coated to a specified thickness, which is monitored during the deposition process.

Here, we report our experimental demonstration of a high-performance temperature sensor fabricated by cascading dissimilar multimode fibers and tapered single mode fiber coated with an index-matching gel of high thermo-optic coefficient. The output power is recorded under varying temperature conditions of the coated material. Besides wavelength-shifting based multimode interferometer sensor, here a unique methodology is adopted where an intensity based fiber temperature sensor is realized. Our optimized design yields a temperature measurement sensitivity of 8.1253 µW/^°C, accuracy of $\pm$ 0.9 ⁰C, response time of 392 ms and resolution of 0.1 ⁰C within the range of 29 °C to 64 °C. Analytical mode overlap and Ansys Lumerical simulation validate experimental results, affirming the method's effectiveness.