Transparent Samples Research Articles

Research on the Method of Depth-Sensing Optical System Based on Multi-Layer Interface Reflection

In this paper, a depth-sensing method employing active irradiation of a semi-annular beam is proposed for observing the multi-layered reflective surfaces of transparent samples with higher resolutions and lower interference. To obtain the focusing resolution of the semi-annular aperture diaphragm system, a model for computing the diffracted optical energy distribution of an asymmetric aperture diaphragm is constructed, and mathematical formulas are deduced for determining the system resolution based on the position of the first dark ring of the amplitude distribution. Optical simulations were performed under specific conditions; the lateral resolution δr of the depth-sensing system was determined to be 0.68 μm, and the focusing accuracy δz was determined to be 0.60 μm. An experimental platform was established under the same conditions, and the results were in accord with those of the simulation results, which validated the correctness of the formula for calculating the amplitude distribution of the diffracted light from the asymmetric aperture diaphragm.

An Attempt to Predict Transparent Armor Ballistic Performance through Quasi-Static Punch Shear Test

Abstract Background Transparent armor systems are traditionally designed following a trial-and-error approach, which involves high development costs associated with ballistic testing. This research article presents a novel methodology, termed quasi-static multi-punch shear testing, within the domain of transparent armor systems. Objective The primary aim is to establish a correlation between multi-hit ballistic tests at Level III-A according to the NIJ 0108.01 standard, achieved through an adaptation of the single-shot ballistic limit methodology, and the quasi-static multi-punch shear testing. The objective is to utilize a simple experimental methodology that provides insights into the multi-hit ballistic behavior of transparent armors. Methods Parameters such as absorbed energy and observed damage mechanisms were utilized to assess the potential relationship between these tests. Transparent armor samples that underwent testing using the quasi-static multi-punch shear test were subsequently cross-sectioned using a water jet cutting machine to facilitate visualization of material damage. In addition, drawing on insights from quasi-static multi-punch shear testing results, the K-means clustering algorithm was employed to predict the likelihood of a specific transparent armor system passing a multi-hit ballistic test. Results Various damage mechanisms were observed as a function of the punch displacement, and correlations were made with the load–displacement curves. Furthermore, the implementation of the K-means clustering algorithm successfully classified transparent armor into two groups: those that passed the ballistic test and those that did not. Conclusions This research significantly advances understanding of transparent armor system behavior under multi-hit conditions and offers a promising predictive tool for evaluating their performance through straightforward and cost-effective experimentation.

A New Method for Measuring Multilayer Thickness Using a Chromatic Confocal Sensor

Multilayer transparent plates play a crucial role in industrial fields, such as optical lenses, electrodes, and solar panels, because of their superior optical and electrical properties. The thickness and uniformity of such plates are decisive for the quality of the final product. However, traditional contact measurement methods are inadequate in accuracy and pose the risk of damaging the plates, making nondestructive measurement of multilayer transparent plate thickness rather challenging. A new measurement technology is urgently needed. This study proposes a new method for the thickness measurement of multilayer transparent plates based on chromatic confocal sensor technology. First, we investigated the dispersive behavior of light in various media layers and derived theoretical measurement models for single-layer and multilayer transparent plate thicknesses. Subsequently, we designed and constructed a measurement system using a C-series chromatic confocal sensor and optical instruments and prepared a five-layer transparent sample consisting of quartz and air layers to confirm the feasibility of the method. The results of the experiment show that the proposed method can accurately measure the thickness of the five-layer sample with a maximum absolute error within 13 µm and a maximum relative error of 4.27%, thus proving its validity, precision, and stability. The results further indicate the high practicality and reliability of this technology in production environments, theoretically enabling the simultaneous measurement of up to 18 layers of the plate and offering broad application prospects in the industry.

An integrated portable system for laser speckle contrast imaging and digital holographic microscopy

A multimodal quantitative phase imaging platform combining digital holographic microscopy (DHM) with laser speckle contrast imaging (LSCI) is demonstrated for imaging weakly scattering and transparent samples in a label-free manner. It uses the principle of coherence of the light source for interferometric detection of phase of transparent and semi-transparent samples. The speckle formation resulting from the coherence property of the laser source is used to track dynamic activities in the regions of interest in the sample. Integration of these two techniques onto a microfluidic chip leads to an optofluidic real-time microscope for live cell imaging applications. In this work, we have developed an integrated multimodal system combining digital holographic microscopy and laser speckle contrast imaging system for Optofluidics and in vitro studies. The sample flowing through the microfluidic channel is imaged to record holograms and video of intensity images at the same time. This enables to map the flow within a microfluidic channel and quantify the channel as well as the particle flow through the channel. The channel morphology along with the particles flowing through the channel are quantified using DHM. The two-dimensional speckle contrast images map the flow of the dynamic microbeads and cells with very high contrast in almost real time. A low-cost portable multimodal quantitative phase microscope combining DHM and LSCI has been demonstrated for real time imaging with applications in optofluidics.

Study on Measurement Method of Three-dimensional Position of Unlabeled Microspheres under Bright Background

Abstract: Using computer vision technology to obtain the position and trajectory data of particle probe microspheres from microscope images has significance and value in the molecular field. However, most of the existing microsphere measurement methods are based on transmission, which can only be measured under transparent samples and substrates and are not suitable for the application scenario of living cell measurement. In this paper, a method based on reflectivity imaging is proposed to measure the three-dimensional position of the dark microspheres in the bright field. Based on the outermost ring radius method, the relationship between the inner ring radius of the microsphere spot and the out-of-focus distance was explored to measure the coordinates in the Z direction. Cardiomyocytes were combined with 10um size silica microspheres. Experiments show that in a bright field with a high perturbation environment, it can achieve high precision measurement of dark microspheres and achieve three-dimensional position measurement with an accuracy of 50nm in XY direction and 100nm in Z direction.

High pressure and high temperature Brillouin scattering measurements of pyrope single crystals using flexible CO2 laser heating systems

Single-crystal Brillouin scattering measurements are important for interpreting seismic velocities within the Earth and other planetary interiors. These measurements are rare, however, at temperatures above 1000 K, due to the fact that the transparent samples cannot be heated by common laser heating systems operating at a wavelength on the order of 1 μm. Here we present Brillouin scattering data on pyrope collected at pressures up to 23.8 GPa and temperatures between 850 and 1900 K using a novel CO2 laser heating system confined in either a flexible hollow silica waveguide or an articulated arm with mirrors mounted in each junction to direct the laser to the exit point. Pyrope has been chosen because it has been extensively studied at high pressures and moderate temperatures and therefore it is an excellent sample for bench-marking the CO2 laser heating system. The new high-temperature velocity data collected in this study allow the room pressure thermal parameters of pyrope to be constrained more tightly, resulting in values that reproduce the temperature dependence of the unit-cell volume of pyrope measured in recent studies at ambient pressure. Aggregate wave velocities of pyrope calculated along an adiabat using the thermoelastic parameters determined in this study are larger than those obtained using published values, implying that velocities for many mantle components may be underestimated at mantle temperatures because high temperature experimental data are lacking.

Effect of Eu Ions Concentration in Y2O3-Based Transparent Ceramics on the Electron Irradiation Induced Luminescence and Damage

Eu3+-doped Y2O3-based luminescent materials can be used as a scintillator for electron or high energy β-ray irradiation, which are essential for applications such as electron microscopy and nuclear batteries. Therefore, it is essential to understand their defect mechanisms and to develop materials with excellent properties. In this paper, Y2O3-based transparent ceramics with different Eu3+ doping concentrations were prepared by solid-state reactive vacuum sintering. This series of transparent ceramic samples exhibits strong red emission under electron beam excitation at the keV level. However, color change appears after the high-energy electron irradiation due to the capture of electrons by the traps in the Y2O3 lattice. Optical transmittance, laser-excited luminescence, X-ray photoelectron spectroscopy (XPS), and other analyses indicated that the traps, or the color change, mainly originate from the residual oxygen vacancies, which can be suppressed by high Eu doping. Seen from the cathodoluminescence (CL) spectra, higher doping concentrations of Eu3+ showed stronger resistance to electron irradiation damage, but also resulted in lower emissions due to concentration quenching. Therefore, 10% doping of Eu was selected in this work to keep the high emission intensity and strong radiation resistance both. This work helps to enhance the understanding of defect formation mechanisms in the Y2O3 matrix and will be of benefit for the modification of scintillation properties for functional materials systems.

Near‐infrared scintillation properties of Nd-doped BaO-Bi2O3-P2O5 glasses

We synthesized BaO-Bi2O3-P2O5 glass samples with different Nd concentrations by the melt-quenching technique. The concentrations were 1.0, 5.0, 10, 15, and 20 %. We obtained transparent and homogeneous samples for 1.0–10 % Nd concentrations. The 15 % Nd-doped sample was inhomogeneous, and the 20 % Nd-doped sample contained a crystalline phase. The photoluminescence (PL) and scintillation properties of the 1.0–10 % Nd-doped samples were investigated. The samples showed PL and scintillation peaks in the near-infrared region, which were due to 4f–4f transitions of Nd3+. We tested the X-ray dose rate response functions of the samples. The 10 % Nd-doped samples showed the most intensive response among the examined samples, and the lower detection limit of dose rate was 0.06 Gy/h with our setup.

Visible/solar light active transparent BiB3O6 glass- ceramics multi-catalysis

Borate based non-centrosymmertic crystals are known for their non-linear optical properties. This study reports BiB3O6 glass-ceramics for photocatalysis and piezocatalysis applications. These were fabricated via. melt-quench technique and yellow transparent glass samples were made. Effectiveness of a bismuth-triborate glass-ceramic (BiB3O6) in degrading methylene blue (MB) and methyl violet (MV) dye undergoing photocatalysis in the presence of visible light and solar light for MB dye was studied. Degradation observed in photocatalysis was ∼62 % and ∼50 % for MB and MV dye respectively in 240 min whereas, ∼72 % of MB dye was degraded under solar light. Piezocatalysis was examined to assess the extended potential of this material, resulting in approximately ∼76 % degradation of MB dye. Moreover, in synergistic photo-piezocatalysis degradation of ∼88 % was observed. Phytotoxicity was also assessed using the germination index (GI) showing ∼76 %, using heat treated sample.

Label-free 3D molecular imaging of living tissues using Raman spectral projection tomography

The ability to image tissues in three dimensions (3D) with label-free molecular contrast at the mesoscale would be a valuable capability in biology and biomedicine. Here, we introduce Raman spectral projection tomography (RSPT) for volumetric molecular imaging with optical sub-millimeter spatial resolution. We have developed a RSPT imaging instrument capable of providing 3D molecular contrast in transparent and semi-transparent samples. We also created a computational pipeline for multivariate reconstruction to extract label-free spatial molecular information from Raman projection data. Using these tools, we demonstrate imaging and visualization of phantoms of various complex shapes with label-free molecular contrast. Finally, we apply RSPT as a tool for imaging of molecular gradients and extracellular matrix heterogeneities in fixed and living tissue-engineered constructs and explanted native cartilage tissues. We show that there exists a favorable balance wherein employing Raman spectroscopy, with its advantages in live cell imaging and label-free molecular contrast, outweighs the reduction in imaging resolution and blurring caused by diffuse photon propagation. Thus, RSPT imaging opens new possibilities for label-free molecular monitoring of tissues.

Off-axis digital lensless holographic microscopy based on spatially multiplexed interferometry.

Digital holographic microscopy (DHM) is a label-free microscopy technique that provides time-resolved quantitative phase imaging (QPI) by measuring the optical path delay of light induced by transparent biological samples. DHM has been utilized for various biomedical applications, such as cancer research and sperm cell assessment, as well as for in vitro drug or toxicity testing. Its lensless version, digital lensless holographic microscopy (DLHM), is an emerging technology that offers size-reduced, lightweight, and cost-effective imaging systems. These features make DLHM applicable, for example, in limited resource laboratories, remote areas, and point-of-care applications. In addition to the abovementioned advantages, in-line arrangements for DLHM also include the limitation of the twin-image presence, which can restrict accurate QPI. We therefore propose a compact lensless common-path interferometric off-axis approach that is capable of quantitative imaging of fast-moving biological specimens, such as living cells in flow. We suggest lensless spatially multiplexed interferometric microscopy (LESSMIM) as a lens-free variant of the previously reported spatially multiplexed interferometric microscopy (SMIM) concept. LESSMIM comprises a common-path interferometric architecture that is based on a single diffraction grating to achieve digital off-axis holography. From a series of single-shot off-axis holograms, twin-image free and time-resolved QPI is achieved by commonly used methods for Fourier filtering-based reconstruction, aberration compensation, and numerical propagation. Initially, the LESSMIM concept is experimentally demonstrated by results from a resolution test chart and investigations on temporal stability. Then, the accuracy of QPI and capabilities for imaging of living adherent cell cultures is characterized. Finally, utilizing a microfluidic channel, the cytometry of suspended cells in flow is evaluated. LESSMIM overcomes several limitations of in-line DLHM and provides fast time-resolved QPI in a compact optical arrangement. In summary, LESSMIM represents a promising technique with potential biomedical applications for fast imaging such as in imaging flow cytometry or sperm cell analysis.

Magneto-Optical Ceramics with High Transparency for Highly Sensitive Magnetometer via Quantum Weak Measurement.

Sensitive magnetometer technology is desirable for biomagnetic field detection and geomagnetic field measuring. Signal amplification materials such as magneto-optical crystals or ceramics are crucial for enhancing detection sensitivity, but severe optical scattering and low Verdet constant further limit its application. To develop high-sensitivity magnetometers for quantum weak measurement schemes, we have conducted investigations on the powder calcining dynamics and prepared a series of high-optical-quality (Ho/Dy)2Zr2O7 transparent ceramic samples. The Verdet constant of magneto-optical materials was measured across a continuous wavelength spectrum, exhibiting a peak at 283 ± 5 rad/(T·m). We further established an electron transition mechanism to elucidate the exceptional magneto-optical attributes of dysprosium. In addition, samples demonstrated superior performance in weak-value amplification, reaching a low detectable magnetic field threshold of 3.5 × 10-8 T and continuously worked over 6 h with high stability. Our work developed a highly sensitive magnetometer using optimized magneto-optical ceramics and provided guidance on design, fabrication, and application for magneto-optical ceramics in quantum weak measurement.

Research on additive manufacturing technology of high solid loading silica glass slurry

In this work, digital light processing (DLP) 3D printing technology was used to fabricate transparent silica glass with complex structures. The effects of different particle sizes and mixing ratios of silica powders on the viscosity of the prepared slurries were investigated. The results showed that when 100–200 nm and 800 nm silica powders were mixed in a 1:4 vol ratio, the slurry exhibited the lowest viscosity. The highest solid loading of the slurry prepared with this mixed silica powder reached 75 wt%, with a viscosity of only 1245 mPa·s. The high solid loading slurry was subjected to 3D printing, debinding, and sintering treatment, and the transparent silica glass samples with complex structures was obtained.

High-quality phase imaging by phase-shifting digital holography and deep learning

Quantitative phase imaging (QPI) technology is widely used in biomedical imaging and other fields because it can realize exact imaging for transparent phase-type samples, which is of great research significance. The complex amplitude distribution of the object wave obtained by phase-shifting digital holography (PSDH) reproduction can provide phase information for QPI, but its existence of phase wrapping and other problems limits its practical application. Although the traditional phase unwrapping algorithm provides a solution, it has problems such as low unwrapping accuracy or long time running. To solve these problems in QPI, a high-quality phase imaging (HQPI) method by PSDH and deep learning (DL) is proposed, where QPI is achieved by extracting the unknown phase shift using a generalized non-iterative phase shift extraction algorithm and unwrapping the wrapped phase by a DL network. Both numerical simulations and optical experiments verify the feasibility of the method. By comparing with the traditional phase unwrapping algorithm, it is demonstrated that the DL unwrapping method has higher unwrapping accuracy and more efficiency. The results show that the method of HQPI is capable of realizing comparatively fast and accurate QPI.

Simultaneous mapping of cathodoluminescence spectra and backscatter diffraction patterns in a scanning electron microscope

Electron backscatter diffraction and cathodoluminescence are complementary scanning electron microscopy modes widely used in the characterisation of semiconductor films, respectively revealing the strain state of a crystalline material and the effect of this strain on the light emission from the sample. Conflicting beam, sample and detector geometries have meant it is not generally possible to acquire the two signals together during the same scan. Here, we present a method of achieving this simultaneous acquisition, by collecting the light emission through a transparent sample substrate. We apply this combination of techniques to investigate the strain field and resultant emission wavelength variation in a deep-ultraviolet micro-LED. For such compatible samples, this approach has the benefits of avoiding image alignment issues and minimising beam damage effects.

High‐Speed High‐Resolution Transport of Intensity Diffraction Tomography with Bi‐Plane Parallel Detection

AbstractA novel high‐speed, high‐resolution 3D microscopy technique named BP‐TIDT is presented that quantifies the refractive index (RI) distribution of label‐free, transparent samples. This method combines a bi‐plane detection scheme (BP) with the transport of intensity diffraction tomography (TIDT), effectively circumventing the need for matched illumination conditions under high numerical aperture (NA) objectives, which enables 15 fps volume rates and 326 nm lateral resolution. The effectiveness and accuracy of the proposed approach are validated through high‐resolution imaging of polystyrene microspheres and HepG2 cells. Moreover, the wide‐ranging applicability of BP‐TIDT is demonstrated by investigating subcellular organelle motion, including mitochondria and lipid droplets, as well as the macroscopic apoptosis process in living COS‐7 cells. To the best of current knowledge, this is the first time that high spatial‐temporal resolution dynamic ODT results are obtained in a non‐interferometric and motion‐free manner, highlighting the potential of BP‐TIDT in advancing research on dynamic cellular processes.

Assessing the light scattering properties of c-Si PV module materials for agrivoltaics: Towards more homogeneous light distribution in crop canopies

Increasing the diffusivity of transmitted light at crop canopies in agrivoltaic (AV) systems remains a desired objective. This is because diffuse light increases the uniformity of light distribution and penetrates deeper into compact crop canopies thereby enhancing the photosynthesis rate and crop yields. Current approaches in greenhouses and open horticultural systems involve the use of diffusing films, diffuse glass, and light diffusing coatings. While these methods are effective, their combination with photovoltaic (PV) modules in AV greenhouses and other AV farming practices remain relatively unknown. However, little to no work has been done to assess the light scattering properties of the existing PV module structural materials such as the glass, encapsulants and the transparent backsheet. This work therefore investigates the light scattering behaviour of c-Si PV module materials through haze and Hortiscatter measurements. 18 samples with the structural layout of glass/encapsulant/encapsulant/back cover (glass or transparent polymer backsheet), applying different commercial encapsulants, were manufactured and tested experimentally. Light in the photosynthetic spectrum was used in the optical characterization of the samples. Furthermore, the impact of UV degradation on the haziness was also tested and the uniformity of the light distribution was further assessed to obtain the Hortiscatter. The findings indicated that (i) Transparent backsheets increased the light diffusivity. (ii) UV degradation reduced the light scattering of most of the PV materials. (iii) For the haziest transparent backsheet sample, the distribution of the transmitted light increased with the incidence light angle and reduced with increasing wavelength in the visible spectrum (iv) Highest haze and Hortiscatter values of up to 80% and 84% respectively were obtained for a sample with glass/TPO/TPO/transparent backsheet layout. (v) Haze and Hortiscatter values could help in optimising the PV module bill of materials for AV applications.

Near 2π solid angle fluorescence collection for laser-induced breakdown spectroscopy.

Detecting heavy metal and radioactive elements distributed in the environment and human body is crucial for life and environmental safety. A lens with a high numerical aperture (NA) is used in laser-induced breakdown spectroscopy to collect the plasma fluorescence as much as possible and improve the limit of detection. However, even a lens with NA up to 0.6, only the fluorescence in a solid angle of 0.4π can be collected. In this work, a novel, to our knowledge, fluorescence collecting scheme composed of a parabolic mirror and a lens is proposed which can collect the plasma fluorescence in a solid angle of ∼1.4π for an opaque material and ∼1.9π for a transparent material. Simulation results show that for opaque samples, this method can improve the fluorescence collection ability by 3.8 times compared to a single lens (NA = 0.5) collection scheme, and for transparent samples 4.5 times may be achieved. In experiments, a 2.8-fold enhancement in the fluorescence collection ability is demonstrated, and the signal-to-noise ratio is increased by 2.5 times for opaque samples.

Velocimetry of GHz elastic surface waves in quartz and fused silica based on full-field imaging of pump–probe reflectometry

This study reports an imaging method for gigahertz surface acoustic waves in transparent layers using infrared subpicosecond laser pulses in the ablation regime and an optical pump–probe technique. The reflectivity modulations due to the photoelastic effect of generated multimodal surface acoustic waves were imaged by an sCMOS camera illuminated by the time-delayed, frequency-doubled probe pulses. Moving the delay time between 6.0nsto11.5ns, image stacks of wave field propagation were created.Two representative samples were investigated: wafers of isotropic fused silica and anisotropic x-cut quartz. Rayleigh (SAW) and longitudinal dominant high-velocity pseudo-surface acoustic wave (HVPSAW) modes could be observed and tracked along a circular grid around the excitation center, allowing the extraction of angular profiles of the propagation velocity. In quartz, the folding of a PSAW was observed. A finite element simulation was developed to predict the measurement results. The simulation and measurement were in good agreement with a relative error of 2% to 5%.These results show the potential for fast and full-field imaging of laser-generated ultrasonic surface wave modes, which can be utilized for the characterization of thin transparent samples such as semiconductor wafers or optical crystals in the gigahertz frequency range.

Double hysteresis (P-E) loops in the transparent composite containing BaTiO3 at room temperature

A transparent composite sample containing BaTiO3 was synthesized by using the melting quenching method. The presence of a glassy phase in this composite sample was detected through XRD analysis, and this was further confirmed by DSC study. TEM and SAED analyses provided evidence that the BaTiO3 nanoparticles/clusters are embedded within the borate glass matrix, establishing the composite nature of this sample. FTIR spectrum of the present sample revealed that the glass matrix is composed of two structural groups (BO3 with NBO’s, and BO4), along with the distinct groups for BaTiO3. XPS spectra of the present composite sample indicated the presence of more than one type of boron, barium, titanium and oxygen. DSC and dielectric studies of the present composite sample revealed the presence of the phase transition temperature (Tc). Dielectric constant (ɛr) and dielectric loss (tan δ) curves of the present composite sample displayed an anomaly peak in the vicinity of TC. The optical transmission spectrum of the present composite sample exhibit two transmission bands of Ti3+ (3d1) ions in tetragonal distorted sites. At room temperature, the present transparent composite sample exhibited double hysteresis loops for BaTiO3 at low electric fields. The results obtained can be used for the development of lead-free ferroelectric material.