Crystal Rod Research Articles

YOLO-PBESW: A Lightweight Deep Learning Model for the Efficient Identification of Indomethacin Crystal Morphologies in Microfluidic Droplets.

Crystallization is important to the pharmaceutical, the chemical, and the materials fields, where the morphology of crystals is one of the key factors affecting the quality of crystallization. High-throughput screening based on microfluidic droplets is a potent technique to accelerate the discovery and development of new crystal morphologies with active pharmaceutical ingredients. However, massive crystal morphologies' datum needs to be identified completely and accurately, which is time-consuming and labor-intensive. Therefore, effective morphologies' detection and small-target tracking are essential for high-efficiency experiments. In this paper, a new improved algorithm YOLOv8 (YOLO-PBESW) for detecting indomethacin crystals with different morphologies is proposed. We enhanced its capability in detecting small targets through the integration of a high-resolution feature layer P2, and the adoption of a BiFPN structure. Additionally, in this paper, adding the EMA mechanism before the P2 detection head was implemented to improve network attention towards global features. Furthermore, we utilized SimSPPF to replace SPPF to mitigate computational costs and reduce inference time. Lastly, the CIoU loss function was substituted with WIoUv3 to improve detection performance. The experimental findings indicate that the enhanced YOLOv8 model attained advancements, achieving AP metrics of 93.3%, 77.6%, 80.2%, and 99.5% for crystal wire, crystal rod, crystal sheet, and jelly-like phases, respectively. The model also achieved a precision of 85.2%, a recall of 83.8%, and an F1 score of 84.5%, with a mAP of 87.6%. In terms of computational efficiency, the model's dimensions and operational efficiency are reported as 5.46 MB, and it took 12.89 ms to process each image with a speed of 77.52 FPS. Compared with state-of-the-art lightweight small object detection models such as the FFCA-YOLO series, our proposed YOLO-PBESW model achieved improvements in detecting indomethacin crystal morphologies, particularly for crystal sheets and crystal rods. The model demonstrated AP values that exceeded L-FFCA-YOLO by 7.4% for crystal sheets and 3.9% for crystal rods, while also delivering a superior F1-score. Furthermore, YOLO-PBESW maintained a lower computational complexity, with parameters of only 11.8 GFLOPs and 2.65 M, and achieved a higher FPS. These outcomes collectively demonstrate that our method achieved a balance between precision and computational speed.

A Functionally Arranged Phononic Crystal Rod Enabling Ultra-Wideband Vibration Attenuation and Orderly Frequency Distillation

In this study, a functionally arranged phononic crystal rod, incorporating sub-periodic structures featuring distinct lattice constants, is designed. This rod seamlessly combines two distinct capabilities: highly efficient broadband vibration suppression and orderly frequency distillation. In the pursuit of this design, the dispersion characteristics of a periodic rod are first analytically calculated to determine the precise cut-on and cut-off frequencies of the resulting band gaps. Following this, the transmission of longitudinal waves traveling through a finite functionally arranged rod is elucidated. Based on these calculations, careful parameter selection yields a compact configuration for a functionally arranged phononic crystal rod, boasting an exceptionally wide band gap spanning frequencies from 100 Hz to 10,000 Hz. Finite element simulations vividly demonstrate its ultra-broadband vibration attenuation capability, nonsymmetrical wave propagation behavior, and orderly frequency distillation phenomenon. Our study underscores the advantages of employing constituent materials with a higher impedance ratio in obtaining a more compact topological structure while preserving the broadband required for vibration attenuation. This research provides essential insights for tackling the need for broadband vibration suppression in engineering and also sets the stage for achieving orderly frequency extraction and energy localization.

The potential of sonocrystallization in crystal habit modification for improving micromeritic and physicochemical properties of Dapagliflozin

Dapagliflozin propanediol monohydrate (DAPA), an antidiabetic drug owing to its needle-shaped crystals exhibits poor micromeritic and physicochemical properties. Crystal habit modification by conventional and sonocrystallization approaches was employed to improve its manufacturability. SEM analysis of sonocrystallized DAPA in acetonitrile (DAPA_SNC3) revealed a rod habit with lower aspect ratio (3.56±0.91) and narrow size distribution (span value-1.37). In case of DAPA_EH and DAPA_CS (solvent evaporation in ethanol:n-hexane, and chloroform, respectively), rod and plate-shaped crystals were obtained with aspect ratios 6.98±5.84 and 6.03±4.21, respectively. All three samples showed significantly improved powder flowability (p<0.0001) compared to DAPA. Further solid-state characterization by FTIR, TGA, DSC, and PXRD showed no polymorphic changes in recrystallized samples. The contact angle studies in water revealed wetting tendency in the following order: SONO_SNC3>SONO_EH>SONO_CS>DAPA. Polar energies of DAPA_SNC3 and DAPA_CS were significantly higher (p<0.01 & p<0.001, respectively) when compared with DAPA. The XPS studies showed increased hydrophilic elements on the surfaces of DAPA_SNC3 crystals which resulted in improved wettability. DAPA_SNC3 among all samples showed highest tensile strength at 200 MPa compression force because of its shape. DAPA_EH showed no significant improvement in IDR profile, while DAPA_CS and DAPA_SNC3 showed significantly faster IDR because of prominent polar functionality (p<0.05 and p<0.0001, respectively).

A photonic crystal waveguide intersection using phase change material for optical neuromorphic synapses

This paper introduces an innovative photonic crystal device that amalgamates a low cross-talk GaAs waveguide intersection with a ring employing phase change material (PCM) for application in all-optical neuromorphic synapses. The device uses a degenerate optical cavity housing Germanium–Antimony-Telluride (GST) phase-change material whose optical properties can be manipulated via a control signal. The proposed design facilitates the development of a non-volatile synapse for photonic neural networks and optical neuromorphic circuits. Numerical simulations using the finite difference time domain method (FDTD) exhibit a notably high-quality factor of 900 and a minimal cross-talk level of −60 dB at the intersection of two waveguides. To validate the FDTD results, the structure undergoes further simulations using the finite element method (FEM), confirming the accuracy of the initial calculations. The resultant structure achieves transmissions of 81 % and 13 % in the amorphous and fully crystalline states of PCM, respectively, enabling low output power in the crystalline state and high output power in the amorphous state. Moreover, modulation of the transmission coefficient between 13 % and 81 % is feasible by manipulating the crystallization coefficient of GST materials. To reduce the effect of the imaginary part of the refractive index of the GST material, the evaluation of the output transmission results for the GSST material (Ge2Sb2Se4Te1) has been performed. The results revealed that, despite having a lower imaginary part of the refractive index compared to GST, GSST exhibits lower absorption in both amorphous and crystalline states. However, the use of GSST materials shows a 27 % reduction in the figure of merit (FOM), indicating a lower effective range and fewer degrees of freedom in the different crystallization levels of the PCM ring. To investigate the effect of fabrication defects and structural sensitivity, the radius of photonic crystal rods and the rings of GaAs and GST have been changed, and the results indicate that the radius of the photonic crystal rods and the GST ring have negligible effects on the output transmission and resonant wavelength. However, the thickness of the GaAs ring shows a high sensitivity, which leads to a change in the resonance wavelength that is utilized as an effective tool for tuning the pass wavelength through the structure within the 171 nm bandgap range. The transmission loss in the amorphous state is −0.6 dB and in the fully crystalline state −7.5 dB, which is attributed to the absorption of GST material. This proposed photonic crystal synapse structure with an area of less than 30 μm2 significantly minimizes the required space compared to similar silicon photonic structures and increases the prospects for integration and scalability. The compatibility of the materials employed with optical fibre communications at the 1310 nm wavelength further bolsters the practical feasibility of this design. In summary, this paper presents a significant advancement in the domain of neuromorphic photonics by introducing a promising structure with substantial potential for neural network synapses.

Celebration of the 50th Anniversary of ISOTT (September 27, 2023 Tokyo, Japan) : ISOTT-A Meaningful Idea That Is Successful.

In the early 1960s, I was working as a traditional chemical engineer studying inanimate objects without the slightest clue of the biological world. At that time, I met Dr Melvin H. Knisely and he encouraged me to use my engineering skills to improve on the Krogh capillary tissue cylinder. I derived a detailed mathematical model and performed a complex computer simulation to achieve that goal. We attended professional meetings on oxygen transport to tissue all over the world, but mainly in Europe, presenting case studies. It became my goal to honour Dr Knisely with a meeting on oxygen transport to tissue at Clemson University in South Carolina, USA. Melvin's wife, Verona, convinced me to also have the meeting at the Medical University of South Carolina located in Charleston, since it was meant to honour Dr Knisely's work with his quartz rod crystal for illumination. He is credited as the first human being to observe the particulate matter in blood flowing in the microcirculation. He was nominated for the Nobel prize four times as a result of his discoveries. When I decided to have part of the meeting at the medical school, I invited Dr Haim Bicher to work with me from there and I focused on Clemson University and the combined meeting structure. As the meeting evolved, we decided it would be a good idea to establish an international society and call it the "International Society on Oxygen Transport to Tissue" (ISOTT). I wrote a paper on the pillars of our young society, "ISOTT from the Beginning: A Tribute to Our Deceased Members (Icons)," and another that shares more detail about its beginnings, "The Founding of ISOTT: The Shamattawa of Engineering Science and Medical Science". The roots of ISOTT are all the members, new and old, who continue to make valuable contributions to an exceedingly important component of human health. I hope that the society lasts for a long time, continuing to make important contributions to the medical world. It is a society that has been instrumental in bringing together brilliant scientists from the medical, engineering, and natural science fields to work together. It has contributed to the evolution of "bioengineering" as we know it today.

Interaction of Y and impurity P on the synergistic enhancement of elongation and electrical conductivity of single crystal copper rod

Single-crystal copper rods with high conductivity and mechanical properties are the decisive material for the production of microwires for chip bonding. To further improve the product of strength and elongation as well as electrical conductivity, rare earth Y is added to a single-crystal copper rod to adjust the microstructure and impurity state. The results show that Cu-0.03Y copper rods have excellent comprehensive properties. The electrical conductivity improves to 103.72 % IACS, and the product of strength and elongation improves to 8.772 GPa%. The precipitates in the Cu-0.03Y single crystal copper rod are nano-sized spherical particles composed of YP (NaCl type) and Cu5Y (Cu5Ca type) phases. The enthalpy of formation of Y and P is calculated using Miedema thermodynamics as ΔH = −173.45 kJ·mol−1. The precipitates formed by the preferential reaction of Y and P reduce the solid dissolved atoms in the copper, and the electrical conductivity increases accordingly. The 〈001〉 texture of a single-crystal copper rod decreases with the addition of Y, while the 〈101〉 texture increases with good plasticity, leading to an improvement in elongation.

A homogenized model for free vibration analysis of finite phononic crystal rods using strain gradient theory

While extensive research has been conducted on elastic wave propagation in infinite phononic crystal (PC) rods, practical applications often involve PC rods of finite length. Therefore, it is essential to consider not only their functional properties, such as wave filtering, but also their mechanical behavior, including free vibration. Motivated by this concern, this study aims to establish a homogenized model for a finite-length PC rod based on the strain gradient theory (SGT) and provide simple closed-form expressions for its natural frequencies. To achieve this objective, an innovative method is developed to determine the material length scale parameters within the SGT. The investigation begins by analyzing the propagation of longitudinal waves in an infinite PC rod. By using the dispersion obtained from Bloch’s theorem as a benchmark, it is demonstrated that the material length scale parameters associated with strain energy and micro-inertial effects in the SGT can be effectively determined by fitting the dispersion obtained from the SGT to the benchmark dispersion obtained from Bloch’s theorem. With the determined parameters, the study proceeds to investigate the free vibration of a finite PC rod. The natural frequencies obtained from both the classical continuum theory (CCT) and the SGT are compared with those calculated by finite element (FE) simulations, which are based on an actual periodic structure and serve as a reliable benchmark. This comparison clearly highlights the superiority of the developed mesoscopic model based on the SGT in accurately predicting the natural frequencies, particularly for higher-order modes, compared to the CCT.

Effect of different retarders on setting time and mechanical properties of hemihydrate phosphogypsum-calcium sulfoaluminate cement composite binder

The optimization of mechanical properties and regulation in setting time of beta-hemihydrate phosphogypsum (β-HPG) are the key to its utilization in building materials. Calcium sulfoaluminate cement (SAC) can significantly enhance the mechanical properties of β-HPG to form a gypsum-based-composite binder, but have little effect on regulating the setting time. Retarders can regulate the setting time of β-HPG but decrease its mechanical properties. However, the synergistic modification mechanism of retarders and SAC on β-HPG has not been clarified. In this paper, the effects of protein retarder (SC) and citric acid (CA) on the setting time, hydration heat, mechanical properties and microstructure of the β-HPG-SAC composite binder were studied systematically. The results show that incorporating SC and CA can effectively regulate the setting time, but the effects on the mechanical properties differ. SC has a certain optimization effect on mechanical properties at low content, but has a negative effect when the content is over 0.2%, while CA has a continuous negative effect with its increasing content. Specifically, SC hinders the formation of the crystalline structure to a certain extent, and makes the crystallization of β-HPG and the hydration of SAC synergistic, while CA delays the hydration process of β-HPG and SAC simultaneously. Different from SC, CA can inhibit the growth of dihydrate gypsum (DH) crystals in the C-axis direction, transforming long rod crystals into short columns, eventually forming a looser microstructure and decreasing mechanical properties. This work provides an effective method for the modification of β-HPG and the high value-added resource utilization of PG.

In situ synthesis of TiB2 rod crystal reinforced PcBN mechanical properties: First-principles calculations and experimental study

In this work, a combination of first-principles calculations and experiments is used to not only reveal the growth mechanism of hexagonal rod-shaped crystals TiB2 and its theoretical influencing factors, but also to experimentally regulate the growth of TiB2 rod-shaped crystals to obtain polycrystalline cubic boron nitride (PcBN) composites with excellent comprehensive mechanical properties. The calculation results reveal that under Ti-rich or B-rich conditions, both the surface energies of (0001) and (101̄0) are lower than the surface energy of (112̄0). The growth of TiB2 is interpreted at the atomic level as being composed of (0001) and (101̄0) surfaces, and it preferentially grows as rod crystals along the (0001) crystal plane. The calculations further indicate that the hexagonal morphology of TiB2 is determined by the atomic concentration within the melt. It exhibits a higher propensity for nucleation under Ti-rich conditions than under B-rich conditions. And it is predicted that a lower relative concentration of Ti atoms promotes the growth of TiB2 into hexagonal rod crystals. In addition, PcBN composites with TiB2 reinforced phase are synthesized in situ by modulating the Ti-Al molar ratio. The experimental results demonstrate that as the concentration of Ti atoms decreases, the nucleation of TiB2 decreases, while the growth of TiB2 rod crystals increases, which aligns with the predicted calculations. Moreover, the presence of rod crystals greatly enhances the densities and flexural strength of PcBN composites. When the Ti-Al molar ratio is adjusted to 1:2, a substantial quantity of high-quality TiB2 rod crystals are cultivated, leading to PcBN composites exhibiting outstanding mechanical properties.

Enhanced dechlorination of 2,4-dichlorophenol using nanorod palygorskite-loaded Fe/Ni nanoparticles: Performance evaluation, influencing factors and action mechanism of Fe and Ni

The basic structural unit of palygorskite (P) consists of rod-shaped crystals with a diameter ranging from 20 to 70 nm. However, due to strong hydrogen bonding and electrostatic forces, most palygorskite rod crystals tend to aggregate, limiting its nanomaterial properties in practical application. To address this limitation, the study focused on dissociating palygorskite aggregates and incorporating them into nanorod palygorskite-loaded Fe/Ni bimetallic nanoparticles (nP-nFe/Ni) synthesis. This approach facilitated the dissociation of palygorskite aggregates and enabled the dispersion of Fe/Ni nanoparticles by palygorskite nanorods. The results revealed that the BET specific surface area of nP-nFe/Ni was significantly higher at 86.17 m2/g compared to 33.62 m2/g for nFe/Ni. Consequently, the dechlorination efficiency of nP-nFe/Ni for 2,4-dichlorophenol (2,4-DCP) at 120 min was 22.4% higher than that of nFe/Ni, despite nP-nFe/Ni containing only 35.1% of the Fe content found in nFe/Ni at the same dosage. Moreover, it was observed that acidic conditions favor maximum dichlorination, while higher temperatures enhance the dechlorination rate. The action mechanism of Fe was identified as the generation of H2, which is catalyzed by Ni to form active hydrogen (H*) that attack the C-Cl bonds of 2,4-DCP for hydrodechlorination. Ni played a vital role in catalyzing H2 conversion to H* , accelerating H2 production by Fe, and inhibiting Fe passivation. These findings are crucial for the application of nano iron technology and nano-scale palygorskite in water and wastewater treatment.

Crystal growth and laser properties of gradual concentration Nd-doped yttrium aluminum garnet serial crystals

The laser crystals of Nd:YAG and Nd:GdYAG with gradual concentration were grown successfully by a Kyropoulos Similar Method. The concentration of boule part of the three grown crystals were 0.17 ∼ 0.38 at% Nd:YAG, 0.95 ∼ 2.86 at% Nd:YAG, and 0.18 ∼ 0.32 at% Nd:GdYAG, respectively. Meanwhile, the absorption coefficients of boule part of the three crystals increased gradually along the growth direction near 808 nm. Three crystal rods with dimensions of Ф 3 × 40 mm were processed from boule part of the grown crystals. The laser performance of the three rods under different transmittance output mirrors and different pump directions were characterized. The optimal laser slope efficiency of 0.17 ∼ 0.38 at% Nd:YAG and 0.18 ∼ 0.32 at% Nd:GdYAG were 52.8% and 55.0%, respectively, when the transmittance of the output mirror was 15%. And the optimal laser slope efficiency of 0.95 ∼ 2.86 at% Nd:YAG was 47.4%, under a 30% transmittance output mirror. Moreover, when the high concentration end is the pump incident end, the laser slope efficiency is reduced. The results show that the laser efficiency can be greatly improved, when pumping along the low concentration end. The gradual concentration crystal is helpful to improve the laser performance.

Relating bulk solid caking events to phase change events that happen during crystallization processes

Caking causes significant problems in the storage of bulk solids in process vessels. Caking results in large rathole formation, lumps in product, inability to empty bags, silos, hoppers, and poor flow in feeders. Caking problems reaches all levels of the production process from the large-scale silos to the small single use packages sold in stores.Caking is characterized as a gain of significant bulk strength during storage. It is responsible for many lost production hours and unscheduled downtimes in processes dealing with bulk solids – particularly powders. Caking is also mechanistic in its nature. In this paper we will deal with one of those causes. The goal of this work is to more clearly understand the relationship between the root cause of caking and the kinetics of the gain of strength observed when recrystallization results in powder caking. Detailed strength measurements seem to indicate that the caking of powders induces a gain in strength in accordance with two exponential growth terms. The first strength growth term is proportional to storage time to the 1st power. The second exponential growth term is proportional to storage time to 3rd power. It was found that this behavior was consistent with phase growth kinetics in accordance with the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. This equation suggests that within a confined space where crystallization is occurring the fraction of space that transforms into a crystalline material has kinetics consistent with exponential functions that are proportional to time to the 1st power, 2nd power, and 3rd power depending on the dimension of the crystals that form. Rods or fibers correspond to kinetics proportional to time to the 1st power. Plates correspond to kinetics proportional to time to the 2nd power. The formation of spheres or 3D clusters correspond to kinetics proportional to time to the 3rd power. The bulk strength tends to have a one-to-one correspondence to exponential crystal growth to time to the 1st and 3rd powers where the 1st power exponential strength growth happens on a short time frame and the 3rd power exponential growth happens on a longer time frame. This suggests that crystal rods or fibers first form in the pendular volume between particles followed by 3D structure formation in the pendules during bulk solid caking events. Understanding the magnitude and kinetics of these events can give engineers the information to prevent or minimize this issue.

A compact high power diode side-pumped 2.09 μm Tm,Ho:YAG laser

We demonstrate a high power compact continuous-wave diode side-pumped Tm,Ho:YAG all solid-state laser at room temperature. A high dopant concentration ratio of Tm,Ho:YAG (3 at.% Tm3+, 0.1 at.% Ho3+) crystal rod with laser diode (LD) side-pumped architecture is employed as a laser head. With a single laser head in a plane-parallel short cavity, a maximum 57 W output power is obtained at a temperature of 19 °C, corresponding to an optical-to-optical efficiency of 10.6% and a slope efficiency of 16.6%. To the best of our knowledge, this is the highest output power of LD-pumped Tm,Ho co-doped laser operating at room temperature. This laser system also exhibits excellent power stability in 90 min, making it widely applicable in various fields.

Novel Piezo-active 2–1–2 Composites with Sets of Large Hydrostatic Parameters

A 2–1–2 composite with two single-crystal components is studied for the first time to highlight large hydrostatic piezoelectric coefficients dh * and gh *, figure of merit dh *gh *, and electromechanical coupling factor kh *. Each 2–1–2 composite contains layers of domain-engineered [011]-poled relaxor-ferroelectric (1–x)Pb(Zn1/3Nb2/3)O3 – xPbTiO3 single crystal (x = 0.0475–0.09) and heterogeneous layers being systems of aligned piezoelectric Li2B4O7 single crystal rods in polyethylene, and these rods have an elliptic cylindrical shape. New diagrams show the volume-fraction ranges wherein large values of dh *> 10−9 C/N, dh *gh *> 2.10−10 Pa−1 and kh *≈ 0.5–0.6 are observed.

Bulk crystal growth and characterization of intrinsic scintillator CaNb2O6

Single crystal CaNb2O6 was grown by the optical floating-zone method and characterized for a new intrinsic scintillator. Under Ar and O2 growth atmospheres, the as-grown crystal rods (Ф 4–5 mm) exhibit a greyish and a colorless appearance, respectively, which are related with the oxygen vacancy. They both show a broad emission band with the maximum at 480 nm under UV excitation, while the one grown in O2 is brighter with a photoluminescence quantum efficiency of 44%. Consequently, a 25% higher scintillation light yield was obtained in the crystals grown in O2 compared to those in Ar. The other scintillation properties including radioluminescence spectrum, pulsed X-ray decay and afterglow were also characterized and compared.

Effect of substrate on vapor-phase crystal growth of diarylethene and photomechanical behaviors of rod crystals

Effect of substrate on vapor-phase crystal growth of diarylethene and photomechanical behaviors of rod crystals

Variation of the coefficient of thermal expansion with the volume ratio of TiB2-Sialon and its influence on the overall performance of PcBN

In this study, the primary factors affecting the performance of PcBN (Polycrystalline cubic boron nitride) tool materials were investigated by high temperature/high pressure sintering through the variation of TiB2-Sialon volume ratio, the strength of TiB2-Sialon binder itself, as well as the matching of the average coefficient of thermal expansion (CTE) with cBN (Cubic boron nitride). The effects of TiB2-Sialon on the phase composition, microstructure, and mechanical properties of PcBN composites were studied by X-ray diffraction (XRD), universal testing machine, scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the properties of TiB2-Sialon binder are analogous to those of the corresponding composites. The phase composition of PcBN composite is not affected by the change of volume ratio. It was found that prepared composite, have TiB2 rod crystals growing along the (100) plane and Sialon rod crystals growing on the (001) plane. The influence of the volume ratio of TiB2-Sialon on the mechanical properties of the composites is principally concerned with the density, mechanical properties, and thermal expansion coefficient of the used binder. The extent to which the binder matches the coefficient of thermal expansion is favorable to the strength of the composite. When the volume ratio of TiB2 to Sialon was 1:3, the hardness (25.21 GPa, 37.44 GPa) and toughness (7.09 Pa m1/2 and 7.48 Pa m1/2) of TiB2-Sialon binder/TiB2-Sialon-cBN composites reached the maximum value, and the optimal impact resistance was also achieved. The density of the binder and the composite material was maximized when the volume ratio is 1:4. The average thermal expansion coefficient of the binder hoc tempore matches comparatively with cBN, and the interface bonding is better, displaying the best flexural strength (805.30 MPa and 1059.60 MPa) and wear ratio (2005). Therefore, adjusting the volume ratio of TiB2-Sialon within a certain range is beneficial to further enhance the binder's strength and mechanical properties.

Improving performance prediction of diode end-pumped solid-state Nd:YAG rod amplifiers by incorporating pump mode evolution.

Master Oscillator Power Amplifier (MOPA) systems find extensive use in laser development to increase the optical power of laser emissions from a Master Oscillator (MO). Commonly used are the cylindrical rod MOPAs that are optically excited using a multimode fiber-coupled (FC) diode laser emission in an end-pumped configuration. Current analytical 3D models that incorporate thermal effects, gain saturation, and iterative Fourier beam propagation methods, collectively, rely on static approximations of the evolution of the FC pump beam profile over the longitudinal volume of the amplifier crystal. Furthermore, in general, the spectral behavior of the FC diode emission is assumed to be static, and the thermal wavelength shift is not accounted for in the simulation. In this work, we demonstrate a novel approach for accurate modeling of the multimode FC pump beam emission as a complex field using a phase-only Gaussian to flat-top (FT) diffractive optical element, thus allowing for the inclusion of the pump beam into the iterative propagation method. Additionally, we present a method for precise calibration of the model using simple experimental measurements of the diode emission spectrum. The theoretical model is experimentally validated using an end-pumped Nd:YAG crystal rod to perform single-pass amplification of a Gaussian beam, showing excellent agreement with predicted output powers over the calibrated range of pump powers. Furthermore, we provide experimental data that exhibits a strong correlation between the Gaussian to FT phase-only transformation and the multimode FC diode evolution in free-space propagation.

Insight into the Viscoelasticity of Self-Assembling Smectic Liquid Crystals of Colloidal Rods from Active Microrheology Simulations.

The rheology of colloidal suspensions is of utmost importance in a wide variety of interdisciplinary applications in formulation technology, determining equally interesting questions in fundamental science. This is especially intriguing when colloids exhibit a degree of long-range positional or orientational ordering, as in liquid crystals (LCs) of elongated particles. Along with standard methods, microrheology (MR) has emerged in recent years as a tool to assess the mechanical properties of materials at the microscopic level. In particular, by active MR one can infer the viscoelastic response of a soft material from the dynamics of a tracer particle being dragged through it by external forces. Although considerable efforts have been made to study the diffusion of guest particles in LCs, little is known about the combined effect of tracer size and directionality of the dragging force on the system's viscoelastic response. By dynamic Monte Carlo simulations, we apply active MR to investigate the viscoelasticity of self-assembling smectic (Sm) LCs consisting of rodlike particles. In particular, we track the motion of a spherical tracer whose size is varied within a range of values matching the system's characteristic length scales and being dragged by constant forces that are parallel, perpendicular, or at 45° to the nematic director. Our results reveal a uniform value of the effective friction coefficient as probed by the tracer at small and large forces, whereas a nonlinear, force-thinning regime is observed at intermediate forces. However, at relatively weak forces the effective friction is strongly determined by correlations between the tracer size and the structure of the host fluid. Moreover, we also show that external forces forming an angle with the nematic director provide additional details that cannot be simply inferred from the mere analysis of parallel and perpendicular forces. Our results highlight the fundamental interplay between tracer size and force direction in assessing the MR of Sm LC fluids.

Luminescence Properties of Epitaxial Cu2O Thin Films Electrodeposited on Metallic Substrates and Cu2O Single Crystals.

The luminescent properties of epitaxial Cu2O thin films were studied in 10-300 K temperature range and compared with the luminescent properties of Cu2O single crystals. Cu2O thin films were deposited epitaxially via the electrodeposition method on either Cu or Ag substrates at different processing parameters, which determined the epitaxial orientation relationships. Cu2O (100) and (111) single crystal samples were cut from a crystal rod grown using the floating zone method. Luminescence spectra of thin films contain the same emission bands as single crystals around 720, 810 and 910 nm, characterizing VO2+, VO+ and VCu defects, correspondingly. Additional emission bands, whose origin is under discussion, are observed around 650-680 nm, while the exciton features are negligibly small. The relative mutual contribution of the emission bands varies depending on the thin film sample. The existence of the domains of crystallites with different orientations determines the polarization of luminescence. The PL of both Cu2O thin films and single crystals is characterized by negative thermal quenching in the low-temperature region; the reason of this phenomenon is discussed.