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Panchromatic dyes have been highly useful in the realm of optical devices. Here, we report that panchromatic dyes with heterohelicenes have been successfully synthesized using a donor‐acceptor strategy. Our synthesis resulted in the creation of π‐extended aza[5]helicene oligomers with butadiyne linkages, which displayed bathochromically shifted absorption and emission spectra. The solvent‐dependent optical measurements revealed the intramolecular charge transfer characteristic of these molecules, and theoretical calculations described the biased molecular orbitals on the azahelicene units that generated the charge‐transfer characteristic. Encouraged by these results, we also prepared donor‐acceptor‐donor dyads using azahelicenes and dimide derivatives, resulting in panchromatic absorbing characteristics covering the range from 250 nm to 800 nm. Theoretical calculations showed the presence of mixed charge‐transfer transitions and localized transitions on the azahelicene units, which led to a broad light‐absorbing property covering the near IR region. Additionally, we conducted measurements of circular dichroism and circularly polarized luminescence for the obtained products. The g‐values were reduced by oligomerization, indicating that the lowest energy transitions were allowed in nature. [ABSTRACT FROM AUTHOR]

Background: Hemolysis in mechanical circulatory support systems is currently determined quantitatively. To also locally resolve hemolysis, we are developing a fluorescent hemolysis detection method. This requires a translucent two‐phase blood analog fluid combined with particle image velocimetry, an optical flow field measurement. The blood analog fluid is composed of red blood cell surrogates. However, producing surrogates in sufficient volume is a challenge. We therefore present a high‐volume and high‐concentration production for our surrogates: ghost cells, hemoglobin‐depleted erythrocytes. Methods: In the ghost cell production, the hemoglobin is removed by a repeated controlled osmolar lysis. We have varied the solution mixture, centrifugation time, and centrifugation force in order to increase production efficiency. The production is characterized by measurements of output volume, hematocrit, transparency, and rheology of the blood analog fluid. Results: The volume of produced ghost cells was significantly increased, and reproducibility was improved. An average production of 389 mL of ghost cells were achieved per day. Those ghost cells diluted in plasma have a rheology similar to blood while being permeable to light. Conclusion: The volume of ghost cells produced is sufficient for optical measurements as particle image velocimetry in mechanical circulatory support systems. This makes further work on experimental measurements for a locally resolved hemolysis detection possible. [ABSTRACT FROM AUTHOR]

Herein, CdTe/MnS core/shell nanoparticles dispersed in an aqueous solution have been synthesized. The formation of MnS semiconductor shell occurs by spontaneous self‐assembly. This process is activated by thermal hydrolysis that removes the excess of thiol and releases S2− ions. In this process, Mn2+ ions on the surface of the CdTe nanoparticles bind to S2− ions to produce a fine semiconducting layer of MnS. Measurements of Raman spectroscopy, optical absorption, and electrochemical measurements are performed. The Raman spectrum shows CdTe characteristic bands at 141 and 163 cm−1. Bands at 221 and 444 cm−1 are associated with the MnS structure. Cyclic voltammetry and differential pulse voltammetry are used to estimate the electrochemical gap at ≈2.47 eV. Absorption optical measurements show tree absorption bands. A broad band between 460 and 520 nm is associated with the first transition in CdTe nanoparticle. The absorption spectrum reveals an optical gap in the range of 2.41–2.33 eV for all the refluxed samples. These values are consistent with those obtained with the electrochemical measurements. The results evidence the formation of a core–shell semiconducting nanostructure made of CdTe nanoparticles coated with a spontaneously self‐assembled thin layer of MnS nanoparticles. [ABSTRACT FROM AUTHOR]

Aim: To develop an accommodating, wide‐angle, schematic eye for emmetropia and myopia in which spectacle refraction and accommodation level are input parameters. Method: The schematic eye is based on an earlier unaccommodated refraction‐dependent eye for myopia developed by Atchison in 2006. This has a parabolic gradient index lens and parameters derived from biometric and optical measurements on young adults. Several parameters are linearly dependent upon spectacle refraction (anterior radius of curvature of the cornea, axial length and vertex radii of curvature and conic asphericities of a biconic retina). The new accommodated schematic eye incorporates accommodation‐dependent changes in several lens‐related parameters. These changes are based on literature values for anterior chamber depth, lens thickness, vitreous chamber depth, lens surface radii of curvature and lens front surface asphericity. A parabolic variation of refractive index with relative distance from the lens centre is retained, with the same edge and centre refractive indices as the earlier model, but the distribution has been manipulated to maintain focus near the retina for the emmetropic case at 0 and 4 D accommodation. The asphericity of the lens back surface is changed so that spherical aberration and peripheral refraction approximately match typical literature trends. The model is used to compare spherical aberration and peripheral refraction in eyes with up to 4 D of myopia and 4 D of accommodation. Results: The levels of spherical aberration in the unaccommodated schematic eyes are similar to literature values for young adults, but the changes in spherical aberration with accommodation are approximately two‐thirds of that found in an experimental study. As intended, peripheral refractions in the accommodated schematic eyes are similar to those of their unaccommodated counterparts. Conclusion: The wide‐angle model extends the range of schematic eyes to include both refraction and accommodation as variable input parameters. It may be useful in predicting aspects of retinal image quality. [ABSTRACT FROM AUTHOR]

• An optical measurement method for total electric field with space charge has been proposed. • The problem of internal polarization and external charge accumulation are solved through self-rotation modulation. • The rotation mode and its impact on sensitivity are studied. • The tests are completed using a small model of a unipolar HVDC transmission line. Researching the measurement of DC total electric field with space charges (Poisson field) can help establish a monitoring system for the electromagnetic environment of UHVDC transmission lines and protect the health of the ecological environment. This paper proposes a DC total electric field optical measurement method based on the Pockels effect and probe self-rotation modulation. It can address the issues of internal charge drift and external charge accumulation in traditional optical probes when measuring DC electric fields with space charges. Theoretical analysis was conducted on measurement under probe rotation, and the optical modulation system was integrated into a probe with dimensions of 60 mm × 30 mm × 20 mm. A self-rotating platform for the probe was designed, and the influence of rotation mode on the results was analyzed. It was found that the sensitivity was higher when using the horizontal-horizontal mode. The signal processing system was tested, showing that the probe retained around 50 % of its original output when rotating at low speeds (frequency 1–3 Hz), fully meeting the measurement requirements. The test platform has been constructed, and the probe's sensitivity was assessed under an AC electric field and validated under a DC electric field. Finally, the optical method proposed in this paper was used to measure the DC total electric field with space charges under a small model of a unipolar HVDC transmission line. Five locations under the line were selected as measurement points, and the results were compared with those obtained from a field mill probe and numerical simulation. This comparison indicates that the proposed method agrees with experimental and simulation results. The average sensitivity of the self-rotating optical probe was 3.71 mV/(kV/m). The error did not exceed 5 % in high-field strength areas (above 20 kV/m) and was also controlled within 15 % in low-field strength areas (below 20 kV/m). [ABSTRACT FROM AUTHOR]

• The thickness estimation method aims at the case of a part of echoes aliasing in picosecond ultrasonics. • A theoretical model of the spectrum relationship between echo-signal regions is constructed. • Simulations are conducted and yield ways to reduce noise impact. • Estimation errors for the tested W/Al bilayer films are within 2.3%. Picosecond ultrasonics (PU) combines the advantages of optical and acoustic measurements, and also provides nanoscale longitudinal resolution, making it the workhorse technique for in-line thickness measurement of opaque submicron films. In PU measurements of multilayer films, echo aliasing often occurs and leads to inaccurate thickness estimation based on straightforward time-domain analysis. This work proposes a model-based thickness estimation method for cases where some echoes are aliased, forming discrete echo-signal regions. The model used is lightweight and does not rely on reference signals obtained from standard specimens. Specifically, a theoretical model is developed to reflect the spectrum relationship between different echo-signal regions in one measurement curve, and is then used to fit the measured spectrum relationship to inversely extract thicknesses. Simulations are conducted and yield ways to reduce noise impact. Eventually, the proposed method is validated through PU measurements of submicron W/Al bilayer films, with estimation errors within 2.3%. [ABSTRACT FROM AUTHOR]

[Display omitted] • YbVO 4 : Er3+/Y3+ phosphor exhibits strong upconversion NIR luminescence. • Defect bands enhance the upconversion NIR luminescence of YbVO 4 : Er3+/Y3+. • Multimode temperature measurement is realized in YbVO 4 : Er3+/Y3+. • The relative sensitivity is higher than most other optical thermometry materials. This study explored the enhancement of near-infrared emissions in YbVO 4 : Er3+ through Y3+ ion doping under a 980 nm laser excitation. The phosphor exhibits weak green emissions at 527 nm (2H 11/2 → 4I 15/2) and 553 nm (4S 3/2 → 4I 15/2), red emissions at 654 nm (4F 9/2 → 4I 15/2), and a strong near-infrared emission at 803 nm (4I 9/2 → 4I 15/2). Optimal doping concentration of Y3+ ion in YbVO 4 : 0.02 Er3+ was determined to be 0.1, resulting in a 7.6-fold enhancement of near-infrared luminescence. This enhancement is attributed to defect bands facilitating energy transfer from green and red levels to the near-infrared levels. Furthermore, a multi-mode temperature sensor based on YbVO 4 : Er3+/Y3+ was developed, offering four distinct temperature sensing modes: TCEL of 2H 11/2 /4S 3/2 , NTCEL of 2H 11/2 /4F 9/2 and 4S 3/2 /4F 9/2 , and single luminescence emission intensity of 4I 9/2 energy level. The sensor demonstrates maximum relative sensitivities of 1.17 % K−1 at 298 K, 0.66 % K−1 at 298 K, 0.41 % K−1 at 298 K and 1.29 % K−1 at 673 K. YbVO 4 : Er3+/Y3+ phosphor exhibits high temperature sensitivity, showcasing significant potential for optical temperature sensing applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Terahertz time-domain spectroscopy for the detection of three types of hemp fibers. • LargeVis dimensionality reduction method applied to THz spectral feature extraction of three hemp fibers. • KNN and DT classifiers applied to three hemp fiber classifications for identification. A novel method for the rapid identification of hemp fibers is proposed in this paper, utilizing terahertz time-domain spectroscopy (THz-TDS) combined with the LargeVis (LV) dimensionality reduction technique. This approach takes advantage of the strengths of THz-TDS while enhancing classification accuracy through LV. To verify the efficacy of this method, terahertz absorption spectral data from three types of hemp fibers were processed. The THz absorption spectra were initially preprocessed using Hanning filtering. Following this, the filtered data underwent dimensionality reduction through three distinct methods: linear Principal Component Analysis (PCA), nonlinear t-Distributed Stochastic Neighbor Embedding (t-SNE), and the LV method. This sequence of steps resulted in a two-dimensional feature data matrix derived from the THz source spectral data. The resultant feature data matrices were then input into both K-Nearest Neighbors (KNN) and Decision Tree (DT) classifiers for analysis. The classification accuracies of six models were evaluated, revealing that the LV-KNN model achieved a 86.67% accuracy rate for the three hemp fiber types. Impressively, the LV-DT model achieved a perfect 100.00% accuracy rate for the same fibers. The LV-DT model, when integrated with THz spectroscopy technology, offers a quick and precise method for identifying various types of hemp fibers. This development introduces an innovative optical measurement scheme for the characterization of textile materials. [ABSTRACT FROM AUTHOR]

• The 22-DHBP and 33-DHBP molecules are encapsulated in the β-CD inclusion complex by solvent, kneading and physical mixing method. • The prepared inclusion complexes' optical and structural properties are evaluated by UV, FL, FT-IR, NMR, TGA and SEM studies. • The binding constant value of 22-DHBP is 8.12 × 103 M-1 and 33-DHBP is 3.15 × 103 M-1. • General mechanism of DHBP/β-CD complex against bacteria cells is proposed. • The antibacterial activity of 22-DHBP/β-CD and 33-DHBP/β-CD inclusion complexes are studied. β-Cyclodextrin plays a vital role in biological application because it can enhance the stability and solubility of the guest molecules in the supramolecular inclusion complexes. Moreover, the β-Cyclodextrin inclusion complex has control-releasing behavior and lower toxicity than bare guest molecules. To improve the solubility and stability properties of two structurally different fluorescent guest molecules, namely 2,2′-dihydroxy biphenyl and 3,3′-dihydroxy biphenyls, they involve the β-Cyclodextrin inclusion complex process. Optical measurements clearly described the efficient binding through the changes in the absorbance and emission intensities of guest molecules in the presence of β-Cyclodextrin. The Job's plot from absorbance measurements reveals the 1:1 stochiometric ratio of binding of guests and the β-Cyclodextrin host. The FT-IR spectra of the solid complex show the characteristic stretching and bending vibrations from both the guests and the host molecule. The 1HNMR spectra of the inclusion complex promote downfield shifting of guest molecule protons upon binding with the β-Cyclodextrin host. The solid complex prepared using the solution method exhibits superior antibacterial activity against both gram-positive and gram-negative bacteria compared to the kneading and physical mixing methods. [ABSTRACT FROM AUTHOR]

• This paper enables non-invasive measurement of the optical rotation angle of human blood at multiple wavelengths. • This paper proposes a multi-wavelength approach to increase the constraint equations in the modeling. • Using a polarization camera as a sensor, this paper proposes to improve the resolution of the light intensity value. • We propose the extraction method of dynamic optical rotation angle to improve the signal-to-noise ratio of the data. • In the predicted results, the correlation coefficient is above 0.80, and the root mean square error is around 2 mmol/L. Measurement of blood glucose concentration is important in the prevention and treatment of diabetes. To improve the measurement signal-to-noise ratio and accuracy, using a polarization camera as the sensor, this paper proposes a multi-wavelength dynamic optical rotation angle method to quantitatively analyze human blood glucose. First, this paper utilizes a split-time approach to drive nine different wavelengths of light sources to work separately to achieve the collection of multiple different wavelengths of data and increase the amount of information. Second, to capture images with an array sensor such as a camera, using space-for-accuracy, this paper uses the cumulative value of the gray values of all pixel points in the image at each angle as the light intensity value to improve the amplitude (light intensity) resolution. Third, the extraction method of the dynamic optical rotation angle in this paper is to extract the difference between the maximum and minimum values of the optical rotation angle from each cycle of the signal of the continuous cyclic change of the length of the optical path, and the accumulated value of the difference of multiple cycles is recorded as the dynamic optical rotation angle, which not only reduces the errors caused by the individual differences, the external environment and the measuring instrument, but also has the effect of averaging and improves the signal-to-noise ratio of the optical rotation angle. To prove the effectiveness of the proposed methods, human finger real and simulation experiments are carried out, respectively. Firstly, the polarization camera is used to collect the image data of elliptically polarized light of nine different wavelengths of linearly polarized light after passing through the human body's finger, and obtains the optical rotation angle under each wavelength that changes with the photoplethysmography (PPG) through data processing, and extracts the dynamic optical rotation angles of the nine wavelengths by the extraction method, and the human body's blood glucose can be quantitatively analyzed. Secondly, this paper builds a simulation model to simulate the blood volume conversion of the human finger, and uses the simulation experimental system to collect the dynamic optical rotation angles of nine wavelengths of a total of 137 human serum samples, and uses partial least squares regression to establish a model between the dynamic optical rotation angles and blood glucose concentration. In the results of predicting all samples using the model, the correlation coefficient and root mean square error were 0.7960 and 2.16 mmol/L, respectively, both of which improved by 137.26 % and decreased by 35.33 %, respectively, compared to the existing method. The experimental results show that the method in this paper has high accuracy in detecting the blood glucose concentration in human beings, which is of great significance in realizing the noninvasive quantitative analysis of human blood glucose components by the polarized light method. [ABSTRACT FROM AUTHOR]

Ultraprecision machining extensively utilizes high-precision displacement sensors due to their exceptional stability, sensitivity, and accuracy. Such sensors can directly measure displacement but are typically components of precision measurement systems, such as atomic force microscopes, profilometers, or coordinate measuring machines. Currently, as displacement sensors are moving towards the direction of high precision, large range, and universal applicability, the market has seen a large variety of new displacement sensor products. However, there is a dearth of comprehensive and systematic reviews of their application specifically in the field of ultraprecision inspection. This review discusses existing research on typical contact and noncontact displacement sensors in high-precision machine tools. First, it reviews and classifies the displacement sensors. Then, it introduces the principles, characteristics, and applications of these types of sensors, along with the technical indicators of their corresponding commercial sensors, and discusses the latest advances in related technologies. Moreover, it also presents a comprehensive summary and comparative study of various high-precision displacement sensors from the perspectives of measurement range, accuracy, resolution, and applicability. Finally, it discusses the technical obstruction and development trends of high-precision displacement sensors. [ABSTRACT FROM AUTHOR]

• A sub-pixel image subdivision scheme for incremental optical encoders is proposed. • The local gradient interpolation is introduced to locate the period with high precision. • A wide range of displacement measurements is achieved by counting pulse. • The experiment verified the high accuracy of the image grating. In the field of precision measurement, subdividing displacement within the grating period to achieve high precision and high resolution remains a significant challenge. For subdivision, traditional optical linear encoders need complex coding and complicated optical systems, which struggle to meet the demands of nanometer measurement. In this paper, based on the fundamental principles of grating displacement measurement, a high-precision peak positioning method from grating images is proposed for linear displacement measurements with nanometer resolution and submicron accuracy. By utilizing a local gradient interpolation algorithm to optimize curves, it could further improve the accuracy of displacement measurement. Experiments demonstrate that this method achieves a resolution of 2 nm and an accuracy of ± 0.1 μm in a range of 50 mm using a grating with a 20 μm period. This sets the groundwork for subdividing optical linear encoders further, the resolution and accuracy could be further improved by optimizing the subdivision method. [ABSTRACT FROM AUTHOR]

The optical fiber ring enhanced detection technology is used to demonstrate a surface plasmon resonance sensing system. The optical fiber sensor has an extended detection range and a high detection rate. We also look into several performance metrics like the figure of merit (FOM), refractive index, absorption, and sensitivity. Based on plasmon-induced absorption (PIA), reflection and the use of silicon optical fiber can improve the sensitivity of (PIA). The experimental results based on fiber ring resonators agree with the stated simulations and measurements based on an optical fiber structure. Thus, the proposed structure provides a new road to optical fiber sensors. [ABSTRACT FROM AUTHOR]

• The Sc 6 WO 12 : Yb3+/Er3+ with strong upconversion red emission were prepared by high-temperature solid phase method. • The optimal doping concentrations of Yb3+ and Er3+ ions in Sc 6 WO 12 were determined to be 0.05 and 0.02, respectively. • The strong red upconversion emission mechanism of the Sc 6 WO 12 : Yb3+/Er3+ phosphor was confirmed as Yb3+(2F 5/2) + Er3+(4I 13/2) → Yb3+(2F 7/2) + Er3+(4F 9/2). • Sc 6 WO 12 : Yb3+/Er3+phosphors have a broad prospect for non-contact temperature sensing applications. Herein, a strong red upconversion phosphor of Yb3+/Er3+ co-doped Sc 6 WO 12 was prepared by employing an equivalent substitution approach. When irradiated by 980 nm near-infrared laser, the phosphor emits strong 660 nm red light. The main excitation mechanism for its red upconversion luminescence emission is the energy transfer process, through which the Er3+ ions is promoted from the 4I 13/2 energy level to the 4F 9/2 energy level. In addition, it is noteworthy that the multimode upconversion luminescence phosphor exhibits three different trends upon temperature change, and its upconversion emission integral intensity ratio exhibits a linear relationship with temperature in the range of 298 K–623 K. This special property makes the phosphor promising for applications in optical temperature measurement. [Display omitted] [ABSTRACT FROM AUTHOR]

• The La 3 Mg 2 NbO 9 :Eu3+,Mn4+ phosphors with dual emission centers were synthesized by solid-state reaction method. • The crystal structure, morphology and luminous performance of La 3 Mg 2 NbO 9 :Eu3+,Mn4+were systematically analyzed. • The s r values of La 3 Mg 2 NbO 9 :Eu3+,Mn4+ sample reach 2.7 % K-1 (@478 K) based on the FIR mode and 5.2 % K −1 (@428 K) based on FIR mode. • The prepared red and white pc-LEDs show excellent performance in plant lighting lamps and WLEDs. In recent years, phosphors have played important roles in solid-state lighting, plant growth lighting and optical temperature measurement. In this work, novel La 3 Mg 2 NbO 9 :Eu3+,Mn4+ phosphors were successfully prepared by the high temperature solid phase method and innovative multimode applications were investigated in optical thermometry, plant growth and White-LEDs. The crystal structure, surface morphology, photoluminescence, temperature sensing properties and luminescence mechanism of La 3 Mg 2 NbO 9 :Eu3+,Mn4+ phosphors were investigated in detail. Benefiting from the different responses of Eu3+ and Mn4+ ions to temperature, the La 3 Mg 2 NbO 9 :0.06Eu3+,0.0095Mn4+ sample shows excellent optical thermometry performance in the range of 303 ∼ 478 K. The maximum values of relative sensitivity (S r) reach 2.7 % K-1 (@478 K) according to the fluorescence intensity ratio method and the maximum of S r is 5.2 % K −1 (@428 K) based on the fluorescence lifetime method. Furthermore, the electrochromic spectrum of the red pc-LED prepared using La 3 Mg 2 NbO 9 :0.06Eu3+,0.005Mn4+ phosphor perfectly overlapped with the absorption bands of the photosensitive pigments for planting, and another white pc-LED prepared using La 3 Mg 2 NbO 9 :0.06Eu3+,0.0025Mn4+ phosphor emitted bright white light with a color rendering index of 89.8, color coordinate of (0.3468, 0.3557) and correlated color temperature of 4945 K. All the results demonstrate that the La 3 Mg 2 NbO 9 :Eu3+,Mn4+phosphors are promising for the field of non-contact optical temperature thermometry, plant lighting lamps and pc-LED backlit displays. [ABSTRACT FROM AUTHOR]

Research on the sensitivity of temperature measurements and optical thermometry involving rare earth ions has been an area of interest in the field of photonics and materials science. Introducing polymer networks as a new host material has an important role due to their properties including a versatile and stable environment for rare earth ions and rapid response in temperature detection. In this work, linear and crosslinked polyethylmethacrylate (PEMA) networks doped with Er3+/Yb3+ (1.5 mol % Er3+, 2 mol% Yb3+) synthesized by free-radical crosslinking polymerization with 0.1 EMA (weight %) at 60 °C were used to investigate direct and indirect optical bandgap energies and Urbach energy from UV–Visible spectra. The Judd-Ofelt (JO) approach was employed to analyze parameters Ω t (t = 2,4,6), spontaneous transition probabilities (Α), branching ratios (β) and radiative lifetimes (τ) as a function of linear and crosslinked PEMA doped nano-crystalline CdNb 2 O 6 : Er3+/Yb3+. The stimulated emission cross-sections of the transitions 2H 11/2 ⟶4I 15/2 , 2S 3/2 ⟶4I 15/2 and 2F 9/2 ⟶4I 15/2 of Er3+/Yb3+ were calculated by two different methods; Fuchtbauer-Ladenburg formula and modified theory, respectively. The gain bandwidth cross-section product for the 2H 11/2 ⟶4I 15/2 was found to be 162.06. 10 − 28 cm 3 , 260.94. 10 − 28 cm 3 and 461.20. 10 − 28 cm 3 of Er3+/Yb3+ embedded in linear, low and high crosslinked PEMA samples, respectively. JO parameters and stimulated emission cross-sections increased; therefore, radiative lifetimes decreased by increasing crosslinking content. In addition, the temperature dependence of upconversion (UC) luminescence was monitored under 975 nm excitation. The fluorescence intensity ratio (FIR) method examined the temperature sensing under two thermally coupled levels at 525 and 548 nm. The maximum sensitivities obtained from the FIR technique within the 300–650 K temperature range shifted to lower temperatures with increasing crosslinker content. Hence, linear and crosslinked polymer hosts doped rare-earth ions can be candidates for remote temperature sensors across various fields. • Introducing PEMA polymers as host materials for CdNb 2 O 6 : Er3+/Yb3+ powders to investigate luminescence properties. • The effect of change in structure and morphology of host on optical properties and Judd-Ofelt parameters. • Usage of PEMA networks for optical thermometry. • Shift in maximum sensitivity as a function of crosslinker contents. [ABSTRACT FROM AUTHOR]

• Optical measurements on impacting fuel spray at non-conventional sets of injection pressure, chamber pressure, wall temperature. • CFD impact spray simulation and validation of the experimental set and data analysis (spray mass, evaporated mass, film mass). • Implementation of a numerical methodology for predicting the local fuel distribution after impact against the piston bowl at GCI engine conditions. This work deals with the experimental and numerical investigation of ultra-high pressure gasoline injection against heated walls in order to characterize the fuel evaporation and distribution in gasoline compression ignition combustion chambers. Spray-wall impingement tests have been conducted in a quiescent vessel and recorded by means of the Mie scattering technique. The test conditions have been set in line with those of a reference benched GCI engine, leading to 500 bar and 700 bar for the injection pressure, 298 K, 423 K, 493 K for the wall temperature, 20 mm and 30 mm for the injector-wall distance. The same test matrix has been reproduced by means of CFD three-dimensional simulations using a proper setting of the wall-impingement model and the joint use of CFD-FEM approaches for the vapour-wall heat exchange. The time evolution of the rebound spray has been recorded and then postprocessed leading to the width and the thickness of the cloud. The CFD results are in line with the experimental ones both in terms of the overall time evolution and punctual values, proving a good accuracy of the simulation in predicting the rebound/adhered fuel mass split and the local distribution of the fuel after the impingement. Given the reliability of the simulations, insights on the numerical wall film mass and evaporated mass have been provided in order to clarify the effect of increasing pressure, temperature, and distance. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper addresses the challenge of precise determination of weld toe radius and flank angle in welded joints. Despite the importance of these parameters for fatigue strength, existing research has not provided clear computational methods for their accurate evaluation. To address this research gap, various evaluation algorithms were developed and applied to both artificially generated profiles of butt-welded and fillet-welded joints and real digital scan data of a reference specimen. The study derives initial recommendations for data quality and the selection of evaluation methods based on weld seam geometry and point spacing. These recommendations consider the demonstrated areas of validity and limitations. The results show that a least squares approach offers the greatest potential to accurately determine weld toe radii. Additionally, the flank angle can be well determined using the gradient of the weld seam profile. The results improve the understanding in assessment of weld seam geometries, enabling automated and precise weld quality inspection in the future. This study may contribute in the future derivation of normative and harmonization regulations for the determination of weld toe parameters. • Contribution to enabling computer-aided automated weld seam inspection. • Detailed depiction and publication of algorithms for determination of weld toe parameters. • Comparison of different approaches for weld toe radius and weld toe angle determination. • The accuracy of the methods depends on point spacing, noise magnitude, and weld shape. • The approach using the least squares method showed the highest robustness. [ABSTRACT FROM AUTHOR]

Graphene quantum dots (GQDs) possess unique optical and biocompatible properties, making them suitable candidates for biomedical and pharmaceutical applications. This study reports the hydrothermal synthesis of pristine-GQD and doped variants: Nitrogen-GQD and Sulfur-GQD. The materials underwent thorough characterization techniques such as UV–vis, fluorescence, XRD, FE-TEM/SEM, EDX, and Raman spectroscopy. The particle sizes of these GQDs range from 2 to 5 nm. We conducted a comprehensive study through MTT assays to evaluate the potential cytotoxic effect of GQD and the doped variants. This study demonstrated their synergistic interactions with an anti-cancer drug, methotrexate (MTX), and also improvement of cytocompatibility in the presence of folic acid (FA). Systematic MD simulations revealed a compacting effect on the dynamic behavior of GQD and its variants in the presence of drugs. Fluorescence spectroscopy and computational modeling suggest non-intercalative surface interactions between GQDs and the drugs. The cytotoxic activity of pristine GQD on HeLa cervical cancer cells is higher than that of N-GQD and S-GQD. When treated with GQD-IC 50 –MTX-IC 50 , only 5.6 % of HeLa cells remained viable. The doped variants exhibited bio-compatibility when tested on normal HEK cell lines. Overall, this study emphasizes the potential of GQDs for targeted cancer therapy through an interdisciplinary approach involving material characterization, computational modeling, and biological assays. [Display omitted] • Pristine GQD and doped variants (N-GQD, S-GQD) were synthesized using hydrothermal method and characterized. • The particle size of S-GQDs is significantly smaller, exhibits higher band gap and amorphous characteristics. • Optical measurements and MD simulations confirmed that neither FA nor MTX intercalate between graphene sheets. • GQD shows significant cytotoxic activity compared to N-GQD and S-GQD. • N-GQD and S-GQD displayed limited MTX activity but demonstrated biocompatible characteristics. [ABSTRACT FROM AUTHOR]

Liquid crystals (LCs) are commonly used to enhance the temperature sensitivity of fiber optic temperature sensors. Most studies utilized non-polymerizable LC-filled optical fibers, which suffer from drawbacks such as complex structure, low temperature detection capability, and narrow measurement range. In this study, a temperature sensor with a wide measurement range, high sensitivity, and simple fabrication process was proposed by directly integrating polymerizable cholesteric liquid crystal (CLC) films onto the end face of optical fibers. The effects of various components in CLC on temperature response were investigated and the temperature sensor fabricated from sample Ⅱ-4 exhibited the best performance. It can detect temperatures ranging from 30 to 270 °C. Within the range of 30–150 °C, its sensitivity is 381 pm/°C, while from 150 to 270 °C, the sensitivity increases to 879 pm/°C. Moreover, it achieves a rapid response time of just 300 ms. Its small size allows monitoring in confined spaces, expanding LC sensor applications. • A temperature sensor integrating polymer liquid crystal films with optical fibers was proposed, enhancing the stability of temperature measurement in optical fiber sensors filled with liquid crystal. • Incorporating the thermally responsive material improved the maximum detectable temperature of liquid crystal-filled temperature sensors and expanded the temperature measurement range. • The sensor features simple fabrication, compact structure, high sensitivity, and with a wide temperature measurement range, making it suitable for temperature detecting micron-scale spaces. [ABSTRACT FROM AUTHOR]

This study investigates the emission mechanism of laser-produced plasma extreme ultraviolet source (LPP-EUV). In the experiment, the EUV radiation is generated by a 1064 nm laser interacting with slab Sn target. The EUV emission is characterized by EUV energy monitors and an EUV spectrometer. The dependency of CE on laser intensity and plasma relative optical depth is explored by a plasma emission-absorption layer model. The dependency is confirmed by an optical interferometry measurement of plasma electron density for the first time. Our work provides a method for characterizing and optimizing the optical depth of laser driven EUV source. • Demonstration of dependency of EUV emission on relative optical depth by angular EUV characterization combined with optical interferometry. • An EUV radiation transportation model containing optical depth as a parameter is proposed. • Angular relative optical depth by laser interferometry verified the EUV radiation transportation model. [ABSTRACT FROM AUTHOR]

• Optical carrier-based microwave interferometry is utilized for pressure sensing. • Theoretical modeling of pressure sensitivity is established and studied in detail. • An artificial neural network-based low pressure demodulation method is developed. • Low pressure distributed measurement is realized with common single-mode fiber. The distributed measurement of low pressure utilizing common optical fibers without sensitization is desired but challenging in many industrial applications. In this paper, with the assistance of machine learning, the distributed measurement of low hydrostatic pressure is realized based on optical carrier-based microwave interferometry (OCMI) employing the common single-mode fiber (SMF). Firstly, the theoretical model of pressure sensitivity is established, and further investigated and validated by numerical simulation and finite element simulation. Subsequently, a distributed hydrostatic pressure measurement experiment is conducted utilizing a common SMF with cascaded weak light reflectors processed along the fiber core. The results indicate that it is difficult to measure low pressure through common fibers based on the traditional demodulation method. To overcome the above limitations, we propose to employ machine learning to analyze the microwave interference information, in order to achieve a one-to-one mapping with the hydrostatic pressure exerted on the sensing fiber. The implementation of distributed pressure measurement is based on the unique advantages of OCMI in terms of physical positioning and reconfigurable gauge length. Meanwhile, different microwave interferometric information is employed as inputs for comparison to select the most effective signals for optimal prediction. The results show that a satisfactory overall measurement and distributed measurement of low hydrostatic pressure can be achieved with the assistance of machine learning, where the accuracy of distributed measurement increases with the increase of Fabry-Perot interferometer (FPI) cavity length. The proposed strategy can be extended to other relatively short-distance spatially continuous distributed or long-distance quasi-distributed fiber sensing systems. [ABSTRACT FROM AUTHOR]

• A cascaded FP cavity and FBG strain sensor on sapphire fibers is developed. • A three-point adhesive bonding process is proposed to greatly improve the adhesion performance. • The fabricated strain sensor can achieve a measurement range of ±1000 με at temperature up to 1150°C. High-temperature strain sensors are key elements for several applications. Key issues of the existing devices include the difficulties of sensor operating above 1000°C as well as the very strong thermal effect under high temperatures introducing significant bias on the strain measurement. Here we developed a cascaded Fabry-Perot cavity and fiber Bragg grating strain sensor fully integrated on sapphire fibers, permitting a sufficient temperature compensation and strain measurement up to 1150°C temperature. A three-point adhesive bonding process is proposed to greatly improve the adhesion performance, and hence the robustness of the device at high temperatures. Experimental results show that the fabricated strain sensor can achieve a measurement range of ±1000 με at temperature up to 1150°C. The experimental results show that the measurement accuracy is not more than 5% at room temperature. the measurement accuracy is significantly decreased at high temperature, and the maximum strain measurement error is 14% at 1150°C. [ABSTRACT FROM AUTHOR]

• R-CIMI expands CMI modes for accurate reflective surface measurement. • Optimized random masks enhance wavefront reconstruction and measurement precision. • Automatic positioning method ensures accurate distance determination. • Experimental validation demonstrates the robustness and accuracy of R-CIMI. This paper proposes a reflection-type surface coherent interferometric modulation imaging (R-CIMI) method based on reference light modulation, leveraging the interference light path generated by the reflected beam of the modulator and the target surface. Furthermore, we present a mask optimization strategy to enhance the similarity of diffraction pattern structures, as well as an automatic positioning approach based on optical field estimation. Owing to the anti-disturbance properties of coherent diffraction imaging, R-CIMI is less susceptible to environmental disturbances than conventional interference techniques. Simulations and experiments demonstrate that the proposed method is comparable to conventional interference methods in terms of measurement accuracy. [ABSTRACT FROM AUTHOR]

• Rotational measurement using coherent optics. • Effect of surface micro-indentations on rotational speed measurements. • Error analysis of rotational speed measurement based on optical coherence technique. • Depth variation calculation by optical coherence technique. Accurate rotational speed measurement is a prerequisite for realizing the condition monitoring and fault diagnosis of rotating equipment. This study proposes a novel rotational speed measurement method based on optical coherent displacement measurement. An optical coherence system is used to measure the relative depth of the shaft surface with uniformly etched micro-indentations on the circumferential surface. Fast Fourier transform (FFT) and the Hanning window energy centrobaric method (HnWECM) are used to process the collected photoelectric signals to obtain depth information and thereby realize the measurement of surface micro-indentations. During the operation, the rotational speed of the shaft is obtained by calculating the ratio of the angular difference between the relative depth of the rectangular pulses of the surface and the time interval. The experimental validation of the response is performed. The experimental results show that in the range of 0 rpm to 60 rpm, the indication error is <1 %, the nonlinearity error is <0.3584 %, and the repeatability error is <0.28 %. In the range of 0 rpm to 600 rpm, the rotational speed measurement method performed well with an indication error of <0.5 %, a maximum nonlinear error of 0.22 %, and a repeatability error of no >0.28 %. Compared with the results reported in existing literature, the proposed method offers advantages in terms of accuracy, linearity, and repeatability. [ABSTRACT FROM AUTHOR]

• Optical mechanics is applied to cylindrical shells. • The theoretical calculation method of DGS under cylindrical shell is established. • Reliability of DGS calculation of cylindrical shell fracture is proved. • Application range of DGS method is extended. In this paper, the transmitted digital gradient sensing (DGS) technique is applied to analyze stress singularity at the tip of an arbitrary oriented crack in a cylindrical shell. A thoretical model of the opitcal path near the tip of the inclined crack in a cylindrical shell under mixed-mode fracture is proposed based on the geometric optical imaging principle. An optical governing equation of DGS technique is established to relate the mixed-mode stress intensity fractors (SIFs) at the crack tip to the shell geometry parameters and the inclined crack sizes, and the angular deflection contours are theoretically plotted using this govering equation. Uniaxial tensile tests are carried out on polymethyl methacrylate (PMMA) cylindrical shells containing an edge crack with different inclined angles, and the optimal calculation area for the exaction of SIFs is determined from linear elasitic fracture mechanics. The effects of shell radius, shell thick, crack length, and crack angle on the mixed-mode SIFs are studied, respectively. These results show that the DGS technique is effective and accurate to evalute the stress singulary around an arbitrary oriented cracks in cylindrical shells. [ABSTRACT FROM AUTHOR]

• Address application limitations of traditional focus variation microscopy. • Determine the optimal parameters for active illumination mode. • Measurement noise immunity enhanced from 8.7 nm to 1.1 nm (50 × objective). • Reconstruct the surface topography of microchannels through transparent encapsulation layer. Optical measurement methods for surface topography offer the advantages of high accuracy, rapid measurement, and non-destructiveness. Each method has its own suitable application scenarios. Among them, focus variation microscopy is extensively employed in precision manufacturing, aerospace, and medical industries due to its ability to measure rough and large slopes surfaces. However, since the measurement depends on local grayscale differences between focused and blurred images, it cannot measure surfaces with low reflectivity or insufficient texture information. In this work, we propose an active illumination mode for focus variation method that utilizes a digital micromirror device (DMD) to generate a checkerboard pattern. This method introduces additional texture information, resulting in a usable local gradient of image grayscale. Additionally, we analyze the selection criteria for the checkerboard pattern parameters, including the period and light-dark ratio. Furthermore, measurements of two standard steps with different heights demonstrate that the measurement repeatability of the proposed method can reach the nanometer level, rendering it suitable for high-precision measurements. More importantly, the measurement noise results indicate significantly superior performance of active illumination mode compared to the uniform illumination mode. Finally, we reconstruct the surface topography of the microchannels in a microfluidic chip through the encapsulation layer, demonstrating the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

Camera imaging through refractive interfaces is a crucial issue in photogrammetric measurements. Most past studies adopted numerical optimization algorithms based on refractive ray tracing procedures. In these studies, the camera and interface parameters are usually calculated iteratively with numerical optimization algorithms. Inappropriate initial values can cause iterations to diverge. Meanwhile, these iterations cannot efficiently reveal the accurate nature of refractive imaging. Therefore, obtaining camera calibration results that are both flexible and physically interpretable continues to be challenging. Consequently, in this study, we modeled refractive imaging by employing ray transfer matrix analysis. Subsequently, we deduced an analytical refractive imaging (ARI) equation that explicitly describes the refractive geometry in a matrix form. Although this equation is built upon the paraxial approximation, we executed a numerical experiment that shows that the developed analytical equation can accurately illustrate refractive imaging with a considerable object distance and a slightly tilted angle of the flat interface. This ARI equation can be used to define the expansion center and the normal vector of the flat interface. Finally, we also propose a flexible measurement method to determine the orientation of the flat interface, wherein the orientation can be measured rather than calculated by iterative procedures. • Proposed an Analytical Refractive Imaging equation that shows the projection of a 3D point onto a 2D image point through a flat interface. • Derived the form of the expansion center and presented a simple calibration method to determine the direction of the refracted interface. • The equation and calibration method offer precise optical measurement alternatives for refracted vision calibration issues. [ABSTRACT FROM AUTHOR]

• A microscale heat-resistant gratings fabrication method suitable for full-field high temperature deformation measurement by grid-based method was proposed. • The fabrication parameter was optimized and the contrast and integrity of the gratings were verified from room temperature to 1000 °C. • Heat-resistant gratings with a pitch of 8 μm were fabricated on the ROI of a Ni based single-crystal superalloy specimen. • Microscale deformation distribution of a Ni based single-crystal superalloy specimen under tensile loading at 900 °C obtained by sampling moiré method. The weak quality of conventional gratings at high temperatures severely limits the application of grating-based methods for high temperature deformation measurements. In this study, a grating fabrication technique with heat-resistant and high adhesion for microscale deformation measurement was proposed. By using UV lithography and metal magnetron sputtering, heat-resistant grating with a pitch of 8 μm was fabricated on the surface of Ni based single-crystal superalloy (NBSC) specimens. Then, the quality of gratings at different magnetron sputtering times was discussed to optimize the fabrication parameters. In application, a high temperature in-situ mechanical experiment system was employed to perform in-situ heating and tensile experiments on NBSC specimens. The results show that the heat-resistant grating maintains excellent contrast and integrality at room temperature (RT) to 1000 °C. The full-field deformation of the NBSC specimen under tensile loading at 900 °C was quantitatively measured by the sampling moiré method, which clearly demonstrates the evolution of plastic localization at the microscale. The heat-resistant grating fabrication technique proposed is simple and easy to implement, showing a promising potential for microscale high temperature deformation engineering applications. [ABSTRACT FROM AUTHOR]

• Utilizing a non-uniform temperature cell is proposed for high temperature spectroscopy. • The proposed method is validated and experimentally demonstrated. • The accuracy of the proposed method is confirmed via simulated composite spectra. • The application of the proposed method is demonstrated experimentally. • The method is expected to be instrumental for high temperature spectroscopy beyond 8 µm. A mathematical method to enable absorption cross-section measurements using an optical cell with a non-uniform temperature distribution is formulated, validated and experimentally demonstrated in this study. The motivation of the proposed method is to facilitate high-temperature spectroscopic studies in the long-wavelength mid-IR region, and to offer an alternative to highly engineered optical cells. The method is based on virtual segmentation of the non-uniform temperature field within an optical cell into bins, each having a sufficiently uniform temperature. By collecting a set of absorbance measurements corresponding to unique temperature profiles and expressing the temperature dependence of the absorption cross-section in terms of a model with limited number of unknowns, a closed-form system of equations is obtained which can be solved to evaluate absorption cross-sections. It is shown, through a set of simulated validation cases, that modeling the temperature dependence in terms of a third order polynomial results in accurate reconstruction of the cross-section spectra for a wide range of cases. Piece-wise polynomials and an alternative nonlinear model are proposed for improved accuracy and to model potentially complex temperature dependencies of the absorption cross-sections. To demonstrate the application of the proposed method, an optical cell with a non-uniform temperature profile was used to measure the cross-section spectra of methane over 1280 – 1330 cm-1 at temperatures up to 523 K. The proposed method is expected to be highly useful in collecting spectroscopic data at high temperatures particularly in the mid-infrared region. [ABSTRACT FROM AUTHOR]

• The small numerical aperture and neighborhood crosstalk from line-scan chromatic confocal measurement are the primary causes for the unimodal feature degradation on the spectral power distribution. • With the unimodal feature degradation, the focused wavelength as an intermediate variable cannot transmit distance information robustly. • The bimodal signal feature obtained by the filter window offset leads to a more robust intermediate variable. • The experiments show that the bimodal signal pattern can achieve a 40% precision improvement in line-scan chromatic confocal measurement. The peak feature of spectral power distribution signals from conventional chromatic confocal measurement degrades significantly as the scanning mode change, which is detrimental to the accuracy and precision of the line-scan chromatic confocal sensor. A bimodal signal pattern is proposed in this paper to solve the peak feature degradation problem. In the bimodal signal pattern, two peak features with smaller full width at half maximum are obtained by offsetting the filter slit. This results in more robust feature localization and more accurate measurement output from the line-scan sensor. Precision calibration experiments conducted on a self-developed line-scan chromatic confocal sensor reveal a remarkable 40% improvement in precision when employing the bimodal signal pattern compared to the traditional unimodal signal pattern with the same hardware configuration. [ABSTRACT FROM AUTHOR]