Search Results (693)

The 795 nm wavelength corresponds to the D1 transition of rubidium atoms and is widely used in atomic optical pumping, atomic clocks, magnetometers, and precision spectroscopy. For compact free-space collimation, beam shaping, and efficient fiber coupling, edge-emitting semiconductor lasers with reduced fast-axis (vertical) divergence are highly desirable, yet low-divergence designs at 795 nm remain limited. Here, we propose and demonstrate low-divergence photonic-crystal epitaxy (LD–PC) for 795 nm edge-emitting lasers. By engineering a periodic n-side photonic-crystal stack to place the fundamental vertical mode near the photonic band edge, the vertical mode is expanded while maintaining effective modal discrimination. Narrow-ridge Fabry–Pérot lasers based on GaAsP/AlGaAs single-quantum-well epitaxy were fabricated and characterized. The optimized LD–PC device (3 μm ridge width, 1 mm cavity length) delivers 227 mW at 200 mA with a threshold current of 23 mA, a slope efficiency of 1.28 W/A, and a peak wall-plug efficiency of 55% under continuous-wave operation at 25 °C. The measured far-field divergences (FWHMs) are 7.16° and 18.83° in the lateral and vertical directions, respectively, corresponding to a reduction in the vertical divergence from >40° in the reference structure to <20° with LD–PC. These results validate photonic-crystal epitaxy as an effective route toward compact, high-performance, low-divergence 795 nm semiconductor laser sources for rubidium-based atomic systems. Full article

Post-appendectomy intra-abdominal abscess (PAA) is a common and problematic complication in children with perforated appendicitis, contributing to prolonged hospitalization, readmissions, and increased healthcare costs. Despite advances in surgical and antimicrobial management, substantial heterogeneity persists in definitions, risk stratification, and treatment strategies. This narrative review aims to synthesize current evidence regarding the pathophysiology, risk factors, diagnostic pathways, clinical impact, and therapeutic approaches to PAA in the pediatric population. PAA occurs predominantly after perforated appendicitis and reflects persistent contamination and fibrin-driven loculation within the peritoneal cavity. Established predictors include fecalith presence, higher perforation severity, and elevated inflammatory markers. Diagnosis is typically established during the second postoperative week using ultrasound as first-line imaging. Management strategies vary widely, ranging from antibiotics alone to percutaneous or surgical drainage. PAA significantly increases length of stay, need for invasive procedures, and healthcare expenditure. In conclusion, PAA remains a clinically significant complication in pediatric perforated appendicitis. Standardized definitions, validated predictive tools, and high-quality trials are urgently needed to harmonize management, optimize outcomes, and reduce variability in care. Full article

Accurate absolute pressure measurement is of great importance in industrial control, environmental monitoring, and aerospace. Traditional fiber-optic Fabry–Perot (F-P) pressure sensors usually involve complex microfabrication and high-cost demodulation systems, while conventional diaphragm capsule sensors are limited in sensitivity and resolution. This work presents a low-cost, high-resolution fiber-optic F-P absolute pressure sensor. The sensor uses a vacuum capsule as one reflective surface and a partially reflective fiber collimator as the other, forming a low-finesse F-P interferometer. The cavity length is linearly modulated by the elastic deformation of the capsule under pressure, and high-precision demodulation is realized using frequency modulated continuous wave (FMCW) interferometry instead of conventional spectral methods. Static experiments from 10 to 110 kPa show that the sensor exhibits a high sensitivity of 15,105 nm/kPa and a resolution of 3.3 Pa. Furthermore, the sensor operates normally within the range of −20 °C to 70 °C, exhibiting a pressure–temperature cross-sensitivity of 0.081 kPa/°C and a cavity length drift of 496 nm/h. With the advantages of high performance, simple structure, low cost, and good scalability by selecting different capsules, the proposed sensor has promising potential for practical applications in pressure measurement fields. Full article

The relationship between lifestyle, ocular biomechanical behavior, and myopia is not well established in the literature. The present study aims to describe changes in ocular biomechanics during adolescence and to explore their relationship with lifestyle factors and myopic progression. Prospective cohort study including 63 adolescents (126 eyes) with a mean age of 14.1 ± 2.6 years old examined twice over a 30 ± 0.9-month period. The data from biomechanics, biometry, corneal tomography, and lifestyle was addressed. The relationships between biomechanical changes, biometric and refractive variation, and lifestyle variables were analyzed using parametric and non-parametric statistics with a significance level of p < 0.05. A biomechanical stiffening trend was found. Axial elongation was 0.12 ± 0.17 mm, and refractive shift was −0.32 ± 0.87 D. The history of allergies was associated with greater axial growth (p = 0.032) and smaller increase in stress–strain-index (SSI) (p = 0.01). Myopization was higher in eyes with ocular surface symptoms (p = 0.049) and those with reported eye-rubbing habits (p = 0.04), with a lower gain in stiffness (p < 0.05). Outdoor activities were associated with higher gain in corneo-scleral stiffness (p < 0.05). Reduced myopization correlated directly with the increase in the SSI (p < 0.05) and inversely with the Integrated Radius (p < 0.05). Greater increases in axial length (AL), vitreous cavity length (VCL), and the ratio between VCL and AL (R_VCL/AL) correlated negatively with the increase in the SSI (p < 0.05). The increase in the R_VCL/AL correlated positively with the time spent on digital devices and negatively with the amount of outdoor activity (p < 0.05). Biomechanics may represent the physiological bridge between the environmental exposure and myopization, as lower gain in corneo-scleral stiffness was consistently associated with greater axial elongation and refractive myopization, with outdoor activity appearing to be protective. Full article

Background and Clinical Significance: Ventriculoperitoneal (VP) shunting remains the standard definitive treatment for progressive neonatal obstructive hydrocephalus. Congenital chylous ascites is an uncommon neonatal condition, most often related to developmental lymphatic abnormalities. The concurrence of hydrocephalus requiring VP diversion with congenital chylous ascites is exceptionally rare and may first become apparent during abdominal access for shunt placement. Awareness of this possibility is clinically important because milky peritoneal fluid at shunt surgery can mimic gastrointestinal injury, and persistent postoperative abdominal fluid collections may be misattributed to shunt-related complications. Case Presentation: A late-preterm female infant (36 weeks’ gestation; birth weight 2.3 kg) presented with congenital hydrocephalus. Cranial ultrasonography was consistent with isolated aqueductal stenosis. Preoperative abdominal ultrasonography demonstrated mild ascites. On 27 May 2025, a VP shunt was placed for obstructive hydrocephalus. Upon entering the peritoneal cavity, milky-white fluid was encountered, prompting concern for bowel injury; however, careful exploration showed no gastrointestinal perforation. Ascitic fluid analysis revealed markedly elevated triglycerides (2300 mg/dL), confirming chylous ascites. The VP shunt was completed without an intraoperative complication. During follow-up, the infant showed appropriate growth (weight 3.0 kg; length 50 cm), while ascites persisted, and she was referred for multidisciplinary evaluation and management. Conclusions: This case highlights an exceptionally rare association of congenital chylous ascites with isolated aqueductal stenosis, identified incidentally during VP shunt insertion. Prompt intraoperative recognition, biochemical confirmation, and coordinated follow-up are essential to distinguish congenital chylous ascites from shunt-related abdominal fluid collections and to guide appropriate multidisciplinary care. Full article

Wind-induced noise remains a critical engineering challenge for MEMS microphones in compact consumer electronics such as smartphones, where spatial constraints limit conventional noise control solutions. This study experimentally investigates the suppression of flow-induced wind noise by a straight tube serving as the front cavity of a microphone, using a precision measurement microphone for data acquisition. Controlled experiments were conducted in both a flow duct for parametric isolation and an anechoic chamber for real-world validation. Results demonstrate a strong diameter-dependent effect: for a 1 mm diameter, increasing tube length significantly reduces noise power spectral density and steepens high-frequency roll-off via enhanced internal viscous and thermal dissipation. This effect weakens for a 2 mm diameter and becomes negligible for a 3 mm diameter, where noise is dominated by external flow excitation at the tube inlet rather than internal propagation. Therefore, extending tube length is an effective noise control strategy only for small-diameter cavities. Furthermore, while increased wind speed and oblique incidence elevate PSD, a longer tube reduces this sensitivity. Because acoustic transmission loss—including potential effects like aperture diffraction and impedance mismatch—was not measured, any resulting improvement in the effective signal-to-noise ratio is strictly presented as a hypothesis requiring future electroacoustic validation. The consistent findings across both experimental environments provide clear design guidance: for compact MEMS microphone systems in portable devices, elongating the front cavity is a viable passive noise control method only when the cavity diameter is sufficiently small (<2 mm). This offers a practical, space-efficient alternative to traditional windscreen-based approaches in portable devices. Full article

This study aims to address the acoustic resonance control problem of a three-dimensional nose landing gear (NLG) cavity. We propose a refined numerical approach based on an eigenvalue solver for the Helmholtz equation. A high-order finite element method (FEM) combined with perfectly matched layer (PML) boundary conditions was employed to accurately capture complex eigenmodes. The radiation damping characteristics of the system were then quantitatively characterized using the quality factor (Q-factor) and resonance frequency. Results indicate that the Helmholtz-type (0,0,0) mode dominates the cavity’s resonance response, with its frequency coinciding with the shear layer-driven Rossiter mode. This study reveals a strong coupling mechanism with the shear-layer-driven Rossiter mode at Mach 0.57, confirming that this interaction is the primary driver of cavity aeroacoustic tonal noise. Taking radiation damping as the core design parameter, a systematic sensitivity analysis was conducted on geometric modifications: aft door length, front door angle, cavity volume, and the introduction of a longitudinal gap. Key findings: shortening the aft door reduces the resonance peak by 8.5 dB; introducing a longitudinal gap with a 10% width reduces the Q-factor by approximately 50%; a combined control strategy (2.5% gap width and 6% cavity volume reduction) achieves 4.9 dB of noise attenuation. Finally, this study establishes a validated acoustic-damping control framework, providing quantitative design criteria and technical guidance for aeroacoustic noise control of NLG cavities. Full article

In micro-opto-electro-mechanical systems (MOEMS), the micro-optical cavity plays a pivotal role. As performance requirements for MOEMS devices continue to rise, these cavities must achieve higher performance levels while simultaneously reducing their physical footprint. However, existing high-precision micro-optical cavities face challenges such as high process sensitivity and conflicting trade-offs between dynamic range and precision. To address these issues, piezoelectric thin-film actuators present a viable solution due to their high precision, stroke flexibility, electromagnetic interference resistance, and structural scalability. This study proposes a piezoelectric thin-film actuator based on the $d_{33}$ mode. The device adopts an island-circular structure that integrates a lead zirconate titanate (PZT) piezoelectric film with metal electrodes. By employing particle swarm optimization (PSO) to enhance displacement output and anti-gravity capabilities, the actuator achieves displacement outputs below 100 nm within a compact form factor while maintaining nanometer-level resolution. Simulation and experimental results confirm a first-order natural frequency of approximately 5.8 kHz, along with a reasonable linear displacement response across a 4–6 V drive voltage range. Furthermore, the device demonstrates functionality within a Fabry–Pérot (F-P) microcavity system, enabling active optical path length modulation through precise cavity tuning. This research provides an effective approach to enhancing the dynamic performance and process compatibility of micro-optical cavity devices, advancing the development of next-generation MOEMS systems. Full article

Spectral demodulation is a crucial component of the extrinsic Fabry–Pérot interferometric (EFPI) sensing technology. In this study, a feedback-based linear spectral fitting demodulation method is proposed for interrogating EFPI sensors. This method utilizes a discrete function derivative and a feedback amplitude calibration technique to extract the complete spectral phase, and the cavity length of the EFPI sensor is determined by performing a linear fit to the relationship between the optical frequency and the spectral phase. The experimental results indicated a nonlinearity of 0.134% over a cavity length range of 50–260 μm, and the resolution was 6.6 nm at a cavity length of 170.210 μm. Pressure measurements obtained with the developed sensor exhibited a nonlinearity of 0.401%. Compared to traditional spectral minimum mean square error algorithms, the proposed method is simpler and faster, making it more suitable for implementation on commodity hardware and better aligned with the practical needs of engineering applications. Full article

The microstructure and ultrastructure of the sperm of Japanese eel, Anguilla japonica, artificially induced with weekly injections with carp pituitary (CP) and human chorionic gonadotropin (HCG), was studied, and milt from 10 out of 20 mature fish was collected. Two distinct morphological structures of A. japonica sperm had been observed with optical microscopy. The cell nucleus of one type of sperm was round or nearly round, the sperm was smaller in size, with 2.57 ± 0.62 μm of the long diameter of the cell nucleus, 2.11 ± 0.59 μm of the short diameter, and 37.35 ± 7.71 μm of the flagellum length. Another type was the eyebrow-shaped sperm, the sperm was relatively larger in size, with 7.66 ± 1.09 μm of the long axis, 2.54 ± 0.46 μm of the short axis, and 38.26 ± 9.02 μm of the flagellum length. By means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the anterior end of the round sperm lacked an acrosomal structure. The implantation fossa was located in the center of the base of the sperm head, and it was in the shape of a channel along the long axis of sperm. The centriolar complex was situated within the implantation fossa. There were 2–3 mitochondria distributed at the basal end of the nucleus. Sperm flagellum prolongated from the sleeve cavity, and the initial part of axoneme connected to the distal end of basal body. The axoneme displayed a typical “9 + 2” pattern. There was a spherical structure in the curving area for eyebrow-shaped sperm, and the axoneme formed a “9 + 0” pattern. The discovery of two different types of sperm in the Japanese eel has provided new perspectives for research on its artificial reproduction. Full article

In the optical fiber Fabry–Perot (FP) multi-dimensional acceleration sensing system, multi-dimensional acceleration measurement is realized based on a single optical path, resulting in the existence of multi-channel interference signals in the spectrum, and the traditional cavity length demodulation algorithm cannot achieve efficient separation of aliasing signals and high-precision demodulation of FP cavity length. To solve this problem, an adaptive filtering–multiple peaks–cooperative least squares algorithm (AF-MP-LS) is proposed for cavity length demodulation of optical fiber FP multi-dimensional accelerometer. The adaptive Gaussian filter is used to dynamically adjust the parameters according to the frequency difference in the aliasing optical signal, and the interference spectra of each channel are efficiently separated. The multiple peaks–least squares method is used to demodulate the separated signals, improve the demodulation resolution, and solve the problem of limited dynamic range of spectral signals. Furthermore, based on the multiplexing structure, a complementary correction method utilizing ‘triple-interferometric’ information—derived from the FP cavities and the auxiliary Michelson interference component—is proposed to improve the demodulation accuracy and stability of the system. The performance of the proposed method was verified through simulations, multi-angle vibration experiments and comparative algorithm analysis. The experimental results show that this algorithm can accurately demodulate multi-dimensional signals under different tilt angles of vibration excitation. Particularly, after compensating for the triple interference information, the mean square error (MSE) of the demodulated acceleration decreased by 0.0044 g, and the accuracy increased by 70.9% compared to before correction. Full article

Surface collisions at Pyrex walls limit the spin coherence in nuclear magnetic resonance gyroscopes (NMRG) vapor cells, while the cavity–stem junction introduces geometry dependent exchange that perturbs the transverse spin relaxation time $T_2$ of ¹²⁹Xe atoms. We combine $T_2$ measurements with Monte Carlo simulations of confined diffusion and surface collisions to decompose the relaxation of Xe atoms and derive a cavity–stem geometry correction for wall relaxation. A structural coupling factor (SCF) is introduced to compress stem length and aperture diameter into a dimensionless metric for diffusion-limited mixing, enabling prediction of the transverse relaxation rate versus geometry. Across eight simulated configurations, the model yields $R^2=0.982$ and agrees with experiments within 7–$9\%$, comparable to the measurement uncertainty ($\pm 0.015{\mathrm{s}}^{-1}$). Using the validated framework, geometry optimization reduces the relaxation rate from $0.225$ to $0.131{\mathrm{s}}^{-1}$ (a $41.8\%$ improvement). This Pyrex surface-collisional analysis provides an in-situ, $T_2$-based route to compare effective surface depolarization across fabrication and surface-treatment protocols while accounting for cavity–stem coupling. Full article

The spotted scat (Scatophagus argus) is a fish species widely distributed in Indo-Pacific waters. In China, females are preferred for aquaculture due to their faster growth rates. Reproduction in teleost fish requires substantial energy, primarily in the form of lipids and fatty acids, which are closely linked to reproductive success and ovarian development. In this study, female spotted scat broodstock were sampled bi-monthly from May 2019 to March 2020 to examine annual ovarian development, lipid droplet accumulation, and fatty acid composition in the liver and ovaries. Body weight, total length, standard length, and condition factor (CF) increased gradually over the sampling period. In July 2019, the gonadosomatic index (GSI) increased significantly, all ovaries reached stage IV, and lipid droplet accumulation was most pronounced. Ovarian saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), n-3 polyunsaturated fatty acids (n-3 PUFA), and n-6 PUFA reached their highest levels in July, whereas the ovarian n-3 PUFA/n-6 PUFA ratio was highest in May. The hepatosomatic index (HSI) was significantly higher from November to March than from May to September. The viscerosomatic index (VSI) was significantly elevated from November to March and in July. Liver lipid droplet accumulation was lowest from May to July. Absolute contents of liver SFA, MUFA, and n-6 PUFA were significantly higher in January and March than in May and July, while liver n-3 PUFA content and the n-3 PUFA/n-6 PUFA ratio peaked in May. These findings indicate that the peak breeding season of spotted scat occurs around July in southern China. From winter to spring, lipids accumulate in the abdominal cavity and liver, likely serving as energy reserves for subsequent ovarian development. The liver appears to play a key role in the uptake and transfer of n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) to the ovaries prior. This study provides useful insights into the reproductive physiology of spotted scat and supports improved broodstock management in aquaculture. Full article

The 6.45 μm mid-infrared laser is highly promising for medical applications due to its efficient tissue ablation with minimal collateral damage. In this work, we demonstrate a stable and compact 10W-level, all-solid-state nanosecond laser source at 6.45 μm based on a Ho:YAG MOPA pumped ring-cavity ZnGeP2 optical parametric oscillator (ZGP OPO). The influence of spot size, phase-matching scheme, and crystal length on the output performance was systematically investigated. Using a 30 mm long Type I ZGP crystal, the system achieved optimal performance: a record-high average output power of 14.6 W at 6.45 μm with an optical-to-optical conversion efficiency of 17.57%, a peak power of 51.7 kW, and excellent power stability (1.45% fluctuation over 120 min at 11.7 W). To our knowledge, this represents the highest reported output power and conversion efficiency for an OPO in this spectral region, surpassing previous sources by an order of magnitude in average power and showing nearly double efficiency. This work provides a stable and reliable laser source tool for application research for techniques such as laser ablation. Full article

The inherently high-voltage-length product (V_πL) of thin-film lithium niobate (TFLN) modulators in the O-, C-, and L-telecom bands restricts further scaling of photonic integrated circuits’ bandwidth density, driving their migration toward shorter operating wavelengths. Nevertheless, the corresponding grating couplers, as critical optical input/outputs (optical I/Os) interfaces, remain largely undeveloped. Here, we demonstrate an 850 nm TFLN grating coupler designed based on topological unidirectional guided resonance (UGR). By breaking C₂ symmetry of the unit cell and precisely tailoring its geometry, we achieve unidirectional upward radiation with a 63.7 dB up/down intensity ratio. Subsequent apodization of groove widths and periods enables precise control of the electrical field distribution in both real and momentum spaces. This yields a vertical-cavity surface-emitting laser (VCSEL)-matched, highly fabrication-tolerant TFLN grating coupler that attains, to the best of our knowledge, the highest simulated coupling efficiency of −0.6 dB without mirrors or hybrid materials. This work delivers a high-efficiency, layout-flexible, and complementary metal oxide semiconductor (CMOS)-compatible optical I/Os solution for short-wavelength TFLN modulators with low V_πL. It offers substantial engineering value and broad applicability for on-chip light source integration and high-bandwidth-density short-reach optical interconnects. Full article