Search Results (272)

The polar oxide Lithium Niobate Tantalate is probed using time-resolved luminescence spectroscopy with the goal of revealing an initial structural insight into the solid solution by analyzing the spectral properties and dynamics of radiatively decaying self-localization phenomena. A blue-green luminescence band can be induced by ultraviolet nanosecond laser pulses with a temperature-dependent intensity and spectral width, pointing to the radiative decay of optically generated self-trapped excitons as its origin, i.e., electron–hole pairs with strong coupling to either the NbO₆- or TaO₆-octahedra. The luminescence decay takes place in the microsecond time range and deviates significantly from a single exponential behavior, so the determined lifetime constants of up to ≈70 μs and stretching factors (1/3–1/5) are validated in more detail using alternative evaluation methods. We discuss our findings, considering the interplay of radiative and non-radiative decay channels, the transition from self-trapped to free excitons, and the presence of a structural disorder of the oxygen octahedra in the solid solutions. Overall, our results suggest self-trapped excitons as local probes for an initial structural elucidation and provide essential information about further experimental and theoretical studies on the atomic structure of Lithium Niobate Tantalate, but also for improving the crystal quality in the framework of applications in photonics and quantum optics. Full article

The effect of Mn-doped zinc ferrite nanoparticles at a low volume concentration (1 × 10⁻⁴) on structural changes in the nematic liquid crystals 6CHBT and 5CB, induced by weak magnetic fields, was investigated using surface acoustic wave (SAW) and light transmission (LT) techniques. Structural changes caused by the applied magnetic field, in both increasing and decreasing modes, as well as after pulsed changes, were examined by measuring the responses of SAW attenuation and LT using a linearly polarized laser beam. The influence of nanoparticle shape (rods, needles, and clusters) and temperature on the structural changes was investigated. A shift in the threshold field and the transition temperature was observed. In addition, the magnetic properties of the individual samples in powder form were examined using M–H curves, M–T curves, and XRD patterns. The results obtained from all measurements are compared, and the effectiveness of each technique, considering the influence of nanoparticle shape and suspension stability, was evaluated. Full article

Silicon carbide (SiC) single crystals are extensively utilized in various fields due to their exceptional properties, such as a wide bandgap and a high breakdown threshold. Nevertheless, the intrinsic high hardness of SiC creates significant challenges for contact machining. This study investigates the surface damage characteristics and underlying mechanisms involved in processing both high-purity silicon carbide (HP-SiC) and nitrogen-doped silicon carbide (N-SiC) crystals using fundamental-frequency nanosecond pulsed lasers. This study establishes a laser-induced damage threshold (LIDT) testing platform and employs the internationally standardized 1-ON-1 test method to evaluate the damage characteristics of HP-SiC and N-SiC crystals under single-pulse laser irradiation. Experimental results indicate that N-SiC crystals exhibit superior absorption characteristics and a lower LIDT compared with HP-SiC crystals. Subsequently, a defect analysis model was established to conduct a theoretical examination of defect information across various types of SiC. Under fundamental-frequency nanosecond pulsed laser irradiation, N-SiC crystals demonstrate a lower average damage threshold and a broader defect damage threshold distribution than their HP-SiC counterparts. By integrating multi-dimensional analytical methods—including photothermal weak absorption mechanisms and damage morphology analysis—the underlying damage mechanisms of the distinct SiC forms were comprehensively elucidated. Moreover, although N-SiC crystals show weaker photothermal absorption properties, they exhibit more pronounced absorption and damage response processes. These factors collectively account for the different laser damage resistances observed in the two types of silicon carbide crystals, implying that distinct processing methodologies should be employed for nanosecond pulsed laser treatment of different SiC crystals. This paper elucidates the damage characteristics of various SiC materials induced by near-infrared nanosecond pulsed lasers and explores their underlying physical mechanisms. Additionally, it provides reliable data and a comprehensive mechanistic explanation for the efficient removal of these materials in practical applications. Full article

Realizing the full potential of optical actuation for high-speed phase-change radio-frequency (RF) switches requires a shift to single-pulse operation. This work presents a systematic investigation of reversible phase transitions in GeTe thin films induced by single 10 ns laser pulses, utilizing spatially resolved characterization techniques, including atomic force microscopy (AFM) and micro-spectroscopy. Precise laser fluence windows for crystallization (12.7–16 mJ/cm²) and amorphization (25.44–41.28 mJ/cm²) are established. A critical finding is that the amorphization process is governed by rapid thermal accumulation, which creates a direct trade-off between achieving the phase transition and avoiding detrimental surface morphology. Specifically, we observe that excessive energy leads to the formation of laser-induced ridges and ablation craters, which are identified as primary causes of device performance degradation. This study elucidates the underlying mechanism of single-pulse-induced phase transitions and provides a practical processing window and design guidelines for developing high-performance, optically actuated GeTe-based RF switches. Full article

Tourmalines from the Anjanabonoina pegmatite field, Central Madagascar, exhibit some of the most complex multi-color zoning patterns known. These tourmalines are also rare because of their unusual Ca- and Li-rich liddicoatite composition. Liddicoatite specimens crystallize in miarolitic pockets in pegmatites, which periodically break open and seal. Multivariate analysis of Laser-Induced Breakdown Spectroscopy (LIBS) spectra of an Anjanabonoina liddicoatite specimen allows evaluation of simultaneous changes in all elements during crystallization. LIBS is an optical emission technique in which photons emitted from a cooling laser plasma are diffracted and recorded as a spectrum. All elements present in the sample at concentrations above their inherent detection limits are represented by peaks in the spectrum. Principal Component Analysis of 123 LIBS spectra acquired in a core-to-rim traverse reveals six major compositional zones that suggest four stages of crystallization, the last three of which begin with the opening of the pocket and mixing of pegmatitic fluids with those from the metasedimentary host rocks. Full article

Alloy gradient-grained structures (represented by copper as a typical single-phase face-centered cubic (FCC) metal), known for their superior mechanical properties such as enhanced strength, ductility, and fatigue resistance, have become increasingly important in aerospace and automotive industries. These alloys are often fabricated using advanced processing techniques such as laser welding, electron beam melting, and controlled cooling, which induce spatial gradients in grain size and optimize material properties by overcoming the traditional strength–ductility trade-off. In this study, a deep learning-based inversion framework combining Convolutional Neural Networks (CNN) and Long Short-Term Memory (LSTM) networks is proposed to efficiently predict key constitutive parameters, such as the initial critical resolved shear stress and hardening modulus, in alloy gradient-grained structures. The model integrates spatial features extracted from strain-field sequences and grain morphology images with temporal features from loading sequences, providing a comprehensive solution for path-dependent mechanical behavior modeling. Trained on high-fidelity Crystal Plasticity Finite Element Method (CPFEM) simulation data, the proposed framework demonstrates high prediction accuracy for the constitutive parameters. The model achieves an error margin of less than 5%. This work highlights the potential of deep learning techniques for the efficient and physically consistent identification of constitutive parameters in alloy gradient-grained structures, offering valuable insights for alloy design and optimization. Full article

We have investigated the structural, morphological, magnetic, and up-conversion luminescence properties of the Yb³⁺/Er³⁺-doped LiGdF₄ nanocrystals precipitated in the silica glassy matrix. Morphological analysis showed uniform distribution of LiGdF₄ nanocrystals (tens of nm in size), embedded in silica glass matrix. FTIR spectroscopy analysis showed trifluoracetates thermolysis with silica lattice formation and structural analysis by XRD is consistent with the LiGdF₄ crystallization process, most likely through an autocatalytic reaction. The stress and crystalline lattice distortion are assigned to the doping and glass matrix environment where the growth process occurs. The EPR spectra associated with the Gd³⁺ ions have shown a well-defined spectrum in the xerogel, associated with the trifluoroacetate ligand environment. In the LiGdF₄ nanocrystals, the broad and unresolved spectrum is due to an envelope of unresolved anisotropic fine structure and a high dipole–dipole interaction between the Gd³⁺/Yb³⁺/Er³⁺ paramagnetic ions. Under 980 nm laser light pumping, we observed the characteristic “blue”, “green” and “red” up-conversion luminescences of the Er³⁺ ions through Yb → Er energy transfer process, that imply three and two-photon process; near UV up-conversion luminescence of Gd³⁺ is observed at about 280–300 nm where Yb → Er and Er → Gd energy transfer is involved. The UC luminescence properties can be improved up to two times by additional Yttrium co-doping due to the induced crystal field distortion. Full article

To address the challenge of laser beam distortion induced by thermal effects in high-power slab laser amplifiers, a coupled thermal–mechanical–optical model for a face-pumped Yb:YAG multi-pass amplifier was developed. The thermal effects under different thermal management strategies were systematically investigated using the finite element method. Firstly, the temperature distribution, thermal stress, and deformation within the Yb:YAG crystal were analyzed and compared under both room-temperature (293 K) and cryogenic (150 K) cooling conditions using a microchannel cooling structure. The results demonstrate that under a pump power of 100 W and room-temperature cooling, the peak temperature of the gain medium reaches 363 K, with a peak thermal stress of 1.04 MPa and a maximum thermal deformation of 1.44 μm. In contrast, under cryogenic cooling at 150 K, the maximum temperature is reduced to 188 K, and both thermal stress and deformation exhibit a more uniform distribution within the pumped region. Subsequently, the thermal lensing of bonded and non-bonded Yb:YAG crystals was compared and analyzed by ray-tracing. It was found that under a pump power of 100 W, the thermal focal lengths of non-bonded Yb:YAG are 1112 mm and 2559 mm at cooling temperatures of 293 K and 150 K, respectively. For bonded crystals with a 3 mm undoped YAG thickness under identical pumping and cooling conditions, the corresponding thermal focal lengths measure 1508 mm and 3044 mm. When the undoped YAG thickness increases to 6 mm, the thermal focal lengths further extend to 1789 mm and 4206 mm, respectively. Full article

Today, the engineering of load-bearing bone tissue after severe trauma still relies on metal-based (Ti, CoCrMo alloys or stainless steel) permanent implants. Such artificial scaffolds are typically applied in the body and come into direct contact with the recipient’s cells, whose adhesion affects the patient’s implant acceptance or rejection. The present study aims to create a nano-rough texture by means of ultra-short femtosecond laser (fs)-induced periodicity in the form of laser induced periodic surface structures (LIPSS) on the surface of a stainless steel implant model, which is additionally functionalized via magnetron-sputtering with a thin Cu layer, thus providing the as-created implants with a stable antimicrobial interface. Calcium phosphate (CaP) crystal growth was additionally applied due to the strong bioactive interface bond that CaPs provide to the bone connective tissue, as well as for the strong interface bond they create between the artificial implant and the surrounding bone tissue, thereby stabilizing the implanted structure within the body. The bioactive properties in the as-created antimicrobial hybrid topographical design, achieved through femtosecond laser-induced nanoscale surface structuring and micro-sized CaP crystal growth, have the potential for subsequent practical applications in bone tissue engineering. Full article

Epitaxial thick films of yttrium iron garnet (YIG) are ideal for use in microwave devices due to their low losses at high frequencies. This report is on the growth of strain-engineered YIG films by liquid-phase epitaxy (LPE) on yttrium aluminum garnet (YAG) substrates with −3% lattice mismatch with YIG. Since the use of a lattice-matched substrate is preferred for LPE growths, a seed layer of YIG, 370–400 nm in thickness, was deposited by pulsed laser deposition (PLD) on (100), (110), and (111) YAG substrates. The seed layers were stoichiometric with magnetic parameters in agreement with the parameters for bulk single-crystal YIG and with strain-induced perpendicular magnetic anisotropy field H_a = 0.19–0.43 kOe. YIG films, 4 to 8.4 μm in thickness, were grown by LPE at 870 °C on YAG substrates with the seed layers using the PbO+B₂O₃ flux and annealed in air at 1000 °C. The films were Y-rich and Fe-deficient and confirmed to be epitaxial single crystals by X-ray diffraction. The saturation magnetization 4πM_s at room temperature was rather high and ranged from 1.9 kG to 2.3 kG. Ferromagnetic resonance at 5–15 GHz showed the absence of significant magneto-crystalline anisotropy in the LPE films with the line-width ΔH in the range 85–160 Oe, and H_a = 0.27–0.80 kOe which is much higher than for the seed layers. The high magnetization and H_a-values for the LPE films could be partially attributed to the off-stoichiometry. Although the strain due to the film–substrate lattice mismatch contributes to H_a, the mismatch in the thermal expansion coefficients for YIG and YAG is also a likely cause of H_a due to the high growth and annealing temperatures. The LPE-grown YIG films with high strain-induced anisotropy fields have the potential for use in self-biased microwave devices. Full article

Axions and axion-like particles (ALPs) are well-motivated dark matter (DM) candidates that couple with photons in external magnetic fields. The parameter space around m a ∼ 50 meV remains largely unexplored by haloscope experiments. We present the first prototype of Weakly Interacting Sub-eV Particles (WISP) Searches on a Fiber Interferometer (WISPFI), a table-top, model-independent scheme based on resonant photon–axion conversion in a hollow-core photonic crystal fiber (HC-PCF) integrated into a Mach–Zehnder interferometer (MZI). Operating near a dark fringe with active phase-locking, combined with amplitude modulation, the interferometer converts axion-induced photon disappearance into a measurable signal. A 2 W, 1550 nm laser is coupled with a 1 m-long HC-PCF placed inside a ∼2 T permanent magnet array, probing a fixed axion mass of m a ≃ 49 meV with a projected sensitivity of g a γ γ ≳ 1.3× 10 − 9 GeV⁻¹ for a measurement time of 30 days. Future upgrades, including pressure tuning of the effective refractive index and implementation of a Fabry–Pérot cavity, could extend the accessible mass range and improve sensitivity, establishing WISPFI as a scalable platform to explore previously inaccessible regions of the axion parameter space. Full article

This study investigates the dynamic magneto-optical properties of ferrofluid thin films, focusing on how magnetic fields induce light–matter interactions using a device known as Ferrocell. Our findings reveal that incident light interacts with self-assembled, anisotropic nanoparticle structures, transforming the ferrofluid into a highly responsive optical medium. Monochromatic laser experiments confirmed the direct correlation between laser color and diffracted light color offering direct insights into particle orientation and aggregate morphology. We observed significant chromatic shifts, especially in regions under strong perpendicular magnetic fields, which provide compelling evidence of structural colors. This phenomenon stems from wavelength-selective interference and diffraction, reminiscent of photonic crystal behavior, yet characterized by short-range order, classifying the material as a photonic glass. Full article

Ultrashort pulsed laser annealing is an efficient technique for crystallizing amorphous semiconductors with the possibility to obtain polycrystalline films at low temperatures, below the melting point, through non-thermal processes. Here, a multilayer structure consisting of alternating amorphous silicon and germanium films was annealed by mid-infrared (1500 nm) ultrashort (70 fs) laser pulses under single-shot and multi-shot irradiation conditions. We investigate selective crystallization of ultrathin (3.5 nm) a-Ge non-hydrogenated films, which are promising for the generation of highly photostable nanodots. Based on Raman spectroscopy analysis, we demonstrate that, in contrast to thicker (above 10 nm) Ge films, explosive stress-induced crystallization is suppressed in such ultrathin systems and proceeds via thermal melting. This is likely due to the islet structure of ultrathin films, which results in the formation of nanopores at the Si-Ge interface and reduces stress confinement during ultrashort laser heating. Full article

In this study, we present a cost-effective approach for fabricating nanopores on single-crystal silicon using a silver–alumina–silver (Ag/AAO/Ag) metal–insulator–metal (MIM) structured mask. Self-ordered porous anodic aluminum oxide (AAO) films were prepared via two-step anodization and coated with silver layers on both sides to form the MIM structure. When irradiated with a 532 nm nanosecond laser, the MIM mask excites surface plasmon polaritons (SPPs), resulting in a localized field enhancement that enables the etching of nanopores into the silicon substrate. This method successfully produced nanopores with diameters as small as 50 nm and depths up to 28 nm. The laser-induced SPP-assisted machining significantly enhances the specific surface area of the processed surface, making it promising for applications in catalysis, biosensing, and microcantilever-based devices. For instance, an increased surface area can improve catalytic efficiency by providing more active sites, and enhance sensor sensitivity by amplifying response signals. Compared to conventional lithographic or focused ion beam techniques, this method offers simplicity, low cost, and scalability. The proposed technique demonstrates a practical and efficient route for the large-area subwavelength nanostructuring of silicon surfaces. Full article

Electrochemical CO₂ reduction reaction (CO₂RR) is a key technology for achieving carbon neutrality and efficient utilization of renewable energy, capable of converting CO₂ into high-value-added carbon-based fuels and chemicals. Copper (Cu)-based catalysts have attracted significant attention due to their unique performance in generating multi-carbon (C₂₊) products such as ethylene and ethanol; however, there are still many controversies regarding their complex reaction mechanisms, active sites, and the dynamic evolution of intermediates. In situ Raman spectroscopy, with its high surface sensitivity, applicability in aqueous environments, and precise detection of molecular vibration modes, has become a powerful tool for studying the structural evolution of Cu catalysts and key reaction intermediates during CO₂RR. This article reviews the principles of electrochemical in situ Raman spectroscopy and its latest developments in the study of CO₂RR on Cu-based catalysts, focusing on its applications in monitoring the dynamic structural changes of the catalyst surface (such as Cu⁺, Cu⁰, and Cu²⁺ oxide species) and identifying key reaction intermediates (such as *CO, *OCCO(*O=C-C=O), *COOH, etc.). Numerous studies have shown that Cu-based oxide precursors undergo rapid reduction and surface reconstruction under CO₂RR conditions, resulting in metallic Cu nanoclusters with unique crystal facets and particle size distributions. These oxide-derived active sites are considered crucial for achieving high selectivity toward C₂₊ products. Time-resolved Raman spectroscopy and surface-enhanced Raman scattering (SERS) techniques have further revealed the dynamic characteristics of local pH changes at the electrode/electrolyte interface and the adsorption behavior of intermediates, providing molecular-level insights into the mechanisms of selectivity control in CO₂RR. However, technical challenges such as weak signal intensity, laser-induced damage, and background fluorescence interference, and opportunities such as coupling high-precision confocal Raman technology with in situ X-ray absorption spectroscopy or synchrotron radiation Fourier transform infrared spectroscopy in researching the mechanisms of CO₂RR are also put forward. Full article