Laser Illumination Research Articles (Page 1)

Abstract This study presents a numerical model of the interference pattern in the reflected light formed by laser illumination of small-sized particles deposited on the surface of a plane-parallel glass plate. Designed with educational use in mind, the model is implemented in Python and incorporates both geometric interference conditions and the angular scattering intensity distribution, the latter approximated using Mie theory. Particle radii are generated according to a lognormal distribution, reflecting the statistical fluctuations characteristic of real powdered materials.
The proposed approach enables interactive visualisation of interference patterns in both two-dimensional and three-dimensional formats, construction of radial profiles, and variation of optical parameters. The numerical model has been tested for stability with respect to random variations in input data and validated through comparison with experimental interference images obtained from fragments of destroyed Lycopodium spore shells and powdered sugar.
The results show good agreement between the numerical model and experimental observations in terms of the positions of interference rings and the shape of the central maximum. The developed tool can be effectively utilised in educational courses on optics at the school and undergraduate levels, offering a practical way to visualise and explore interference phenomena. The source code is freely available and designed for use by students with minimal programming skills, for reproduction, modification, and integration into teaching activities or student-led research projects.

Reduced graphene oxide (rGO) and polyvinylpyrrolidone (PVP) are promising materials for the development of advanced nanocomposites due to the excellent electrical conductivity of rGO and the ability of PVP to stabilize dispersions of nanomaterials. In this study, we present the synthesis, characterization, and optoelectronic performance of PVP@rGO nanocomposites. Graphene oxide (GO) was synthesized via a modified Hummers’ method and reduced to rGO, which was then incorporated into PVP to form stable composites. The PVP@rGO composites were characterized using X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and UV–visible spectroscopy. The XRD pattern shows a broad (002) reflection of rGO near 25°, indicative of turbostratic graphitic ordering. The calculated average crystallite size, using the Debye–Scherrer equation, is approximately 4.5 nm, suggesting partially restacked nanosheets within the composite matrix. FTIR spectra indicated the reduction of GO to rGO, with the disappearance of oxygen‐containing groups and the appearance of characteristic CC bonds. SEM imaging revealed uniform dispersion of rGO within the PVP matrix, and UV–visible analysis showed a shift in the optical bandgap with increasing rGO content. The fabricated lateral‐type photodetector exhibited a strong and stable photocurrent response under 375 nm laser illumination, achieving a photoresponsivity of 98.39 A W −1 , a specific detectivity of 1.12 × 10 12 Jones, and a photosensitivity of 1.37 × 10 3 . These results demonstrate the excellent light‐to‐current conversion efficiency and highlight the promise of PVP@rGO nanocomposites for next‐generation optoelectronic and photodetection applications.

The role of cellulose nanoparticles in enhancing human iPSC compatibility with composite conductive PANI/cellulose films.

Two-dimensional noble transition metal chalcogenides (NTMCs) are of potential use for creating high-performance electronic and optoelectronic devices. However, the direct growth of high-quality multicomponent NTMC materials remains a significant challenge. Herein, we report the successful fabrication of quaternary AuPdNaS2 nanoribbons on a Au foil substrate by an ambient-pressure chemical vapor deposition approach. The vibrational properties and carrier dynamics of AuPdNaS2 nanoribbons are experimentally elucidated using temperature-dependent Raman spectroscopy and ultrafast optical pump-probe spectroscopy. In addition, the AuPdNaS2 photodetector exhibits a high photoresponsivity of 235.5 A/W and a good detectivity of 1.21 × 1012 Jones under 660 nm laser illumination. This work demonstrates the synthesis of quaternary AuPdNaS2 and paves the way for multicomponent NTMC materials in optoelectronic applications.

There is a recent upsurge of interests in flat bands in condensed-matter systems and the consequences for magnetism and superconductivity. This article highlights the physics, where peculiar quantum-mechanical mechanisms for the physical properties such as flatband ferromagnetism and flatband superconductivity that arise when the band is not trivially flat but has a strange Hilbert space with non-orthogonalisable Wannier states, which goes far beyond just the diverging density of states. Peculiar wavefunctions come from a quantum-mechanical interference and entanglement. Interesting phenomena become even remarkable when many-body interactions are introduced, culminating in flatband superconductivity as well as flatband ferromagnetism. Flatband physics harbours a very wide range physics indeed, extending to non-equilibrium physics in laser illumination, where Floquet states for topologcial superconductivity is promoted in flatbands. While these are theorecially curious, possible candidates for the flatband materials are beginning to emerge, which is also described. These provide a wide and promising outlook.

Precise control of light-induced electrical signals at the biotic-abiotic interface remains a central challenge in advancing next-generation bioelectronic systems. In particular, achieving bidirectional signal modulation is essential for effective neural interface applications. Here, a spatially resolved, bidirectional photoelectric response at the silicon (Si) membrane-solution interface, induced by laser illumination is presented. Notably, a clear reversal in signal polarity between the illuminated regions (bright zones) and adjacent non-illuminated areas (dark zones) is observed. This signal orientation can be dynamically tuned by adjusting the light spot position and tailoring interfacial properties. To understand the underlying mechanism, the author systematically examined how various experimental parameters influence photoelectric behavior. These include the choice of adhesive, substrate conductivity (conductive vs insulating), boundary conditions (fixed vs free edges), and membrane geometry (e.g., grids and rectangles). These results reveal a cooperative effect between intrinsic charge conservation in the Si membrane and capacitive coupling at the interface. Moreover, in vivo studies show that integrating a conductive substrate beneath the Si membrane significantly enhances the modulation of sciatic nerve activity. Together, these findings define a new framework for light-responsive bioelectronic interfaces and point toward their broad utility in bioelectronic and neuromodulation applications.

A practical procedure to accurately characterize three-dimensional (3D) arrangements of particles using the direct imaging method is systematically investigated using Langevin dynamical simulations. The radial distribution function (RDF) calculated from the 2D projection illuminated by a laser sheet with the optimized thickness g2D(r) can be very close to the RDF of the corresponding 3D Yukawa fluid g3D(r). It is found that, as the illumination thickness gradually decreases from around the interparticle distance b, the difference between g2D(r) and g3D(r) first decreases substantially and then increases back. The obtained optimized illumination thickness 0.2b here just corresponds to the minimum difference between g2D(r) and g3D(r), which, in fact, decreases gradually with the system size. Based on the accurately determined RDF from the 2D projection, various physics quantities of the studied 3D systems can also be accurately obtained, such as the internal energy and pressure. By adding two more cameras, the anisotropic 3D structure of polycrystalline systems can also be determined, where the optimized illumination laser sheet should include at least one unit cell for all three directions, significantly thicker than that for liquids. The suggested practical procedure here can be used in the experimental analysis of microgravity dusty plasmas, colloids, and other 3D systems, where individual particles can be identified.

Perforated appendicitis is a common and morbid pediatric surgical condition frequently requiring prolonged antibiotic therapy. Adjunctive intraoperative strategies for local antimicrobial therapy are limited, and photodynamic therapy (PDT) may offer a targeted, resistance-independent approach. To evaluate the feasibility, safety, and preliminary efficacy of laparoscopic methylene blue photodynamic therapy (MB-PDT) for intra-abdominal disinfection in a rabbit model of perforated appendicitis. Experimental preclinical animal study conducted between 2023 and 2025. Single-center laboratory-based animal research facility affiliated with an academic medical center. Nineteen New Zealand White rabbits underwent surgically induced perforated appendicitis with peritonitis via appendiceal ligation and electrocautery perforation. Rabbits received laparoscopic MB-PDT (n=9) or control conditions (methylene blue only, no light; n=10) 24 - 40 hours after appendiceal perforation. MB-PDT involved peritoneal lavage with 300 µg/mL methylene blue, followed by 665 nm laser illumination to 25 J/cm 2 . Peritoneal aspirates were collected before and 24h after intervention. Bacterial burden was quantified, and isolated bacteria were submitted to in vitro PDT. Tissue samples from intraperitoneal organs were collected 24 hours post-intervention. Primary outcomes included feasibility of PDT delivery, safety (histologic evidence of off-target injury), and preliminary in vivo efficacy (change in bacterial burden pre-vs. post-intervention). Secondary outcomes included clinical parameter changes and in vitro MB-PDT efficacy. Of the 14 rabbits that developed peritonitis, 10 (age 5-6 months, weight 3.1-3.8 kg) completed follow-up. Laparoscopic MB-PDT delivery was feasible and caused no off-target histologic injury. Bacterial burden increased in MB-PDT animals relative to controls, though not significantly (p=0.18). Post-intervention, body temperature showed a trend toward reduction in MB-PDT animals (-0.37 ± 1.32°C) vs controls (0.26 ± 0.76°C; p=0.27). In vitro MB-PDT significantly reduced bacterial burden for all tested species (p<0.001), with greater efficacy in Gram-positive bacteria. Laparoscopic MB-PDT was feasible and safe in a rabbit model of perforated appendicitis, with high in vitro antimicrobial efficacy. Although in vivo bacterial reduction was not demonstrated, these results support further investigation of MB-PDT as a novel intraoperative adjunct for treating intra-abdominal infection.

This study presents a novel photovoltaic triboelectric nanogenerator (PTENG) that operates on sliding contacts between n-type (gallium arsenide) GaAs and metal electrodes in the presence of periodic light illumination, which offers harvesting energy synergistically by integrating both photovoltaic and triboelectric effects to enhance the energy output. Using an in-house built test setup with provision of laser illumination, the open-circuit voltage (VOC) and short-circuit current (ISC) were measured for the n-GaAs semiconductors with different metal contacts (Al and Cu). Under both laser light (630 nm) and without laser light conditions, n-GaAs with aluminum contacts exhibited the highest VOC and ISC values, reaching up to 11.2 from 9.0 V and 9.5 from 6.2 μA. The Voc and ISC values with the copper contact were improved to 6.6 from 4.0 V and 4.3 from 2.5 μA under laser illumination and no laser illumination conditions. The photovoltaic effect contributed more significantly than triboelectrification to the output, with electron-hole pairs generated under light further increasing VOC and ISC in alignment with triboelectric charges. Atomic force microscopy and Kelvin probe force microscopy revealed a contact potential difference of 10 mV under laser exposure, confirming enhanced charge separation. The optimized PTENG achieved a maximum power density of 6.8 W/m2 at a 100 kΩ load, which was sufficient to power multiple light-emitting diodes (LEDs) and effectively charge a 1.0 μF capacitor. Performance improvements were further supported by increased sliding speed and larger contact areas. This work demonstrates the potential of PTENGs that combine triboelectric and tribo-photovoltaic effects for efficient and practical energy-harvesting applications.

It is essential that the design of atomizing sprays be tailored to the specific requirements of various industrial processes within, e.g., the agricultural or energy sector. However, the measurement of key atomizer parameters-central to the optimization of such systems-suffers from time-intensive techniques, complex calibration routines, and/or the need to include additives in the injected liquid. Here, we present an additive-less, two-dimensional optical technique for determining droplet sizes, number densities, and liquid volume fractions of optically dense atomizing sprays. This method is applied to characterize two distinct hollow-cone sprays injected at high pressure and flow rate. Our results reveal local inhomogeneities in various key atomizer parameters, demonstrating the potential for efficient, in situ characterization of atomizing spray systems.

Surface termination of semiconductors is important for their applications in electronics because it governs electrical properties at interfaces. For quantum sensors and qubits based on spins in solids, this is crucial when they are located a few nanometers below the crystal surface. In the case of diamond, oxygen termination is preferential for quantum sensing with nitrogen-vacancy (NV) centers. Here, we present local surface modification of a nonconductive diamond surface utilizing conductive atomic force microscopy under laser illumination. By applying this method, we demonstrate not only a removal of fluorescence background but also control over the charge state of single NV centers. The latter show an improvement of the optically detected magnetic resonance contrast from 1% up to 29% after the treatment. We assume that local surface oxidation is happening on the diamond, which has already been demonstrated for conducting hydrogenated surfaces, but its implementation to nonconductive surfaces remains challenging.

Abstract Inventing new approaches to transform abundant plant matter swiftly into valuable products is crucial for sustainable development. Here, the first direct and continuous conversion of lignocellulosic solid mass into synthetic biogas is reported using blue laser irradiation at multi‐kW/cm2 intensity. It is demonstrated that the on‐demand generation of a biogas jet, achieving rapid (in milliseconds) and continuous production of a flame jet 300 times larger than the mm‐size laser focus. Remarkably, biogas production occurs exclusively during laser illumination, without triggering bulk combustion, and achieves up to 92% mass conversion. A comprehensive phase diagram of the blue light–wood interaction highlighting three distinct regimes accessed is reported by varying laser parameters and provide mechanistic insight using photothermal simulations. Furthermore, the molecular composition of the synthetic biogas is identified and is shown to result from the photothermal decomposition of lignocellulose molecules. The biogas, collected independently, is shown to produce a sustained flame. Successful bio‐gasification of 16 kinds of woods proves that the all‐optical approach is solvent‐free, non‐contact, scalable, and universally applicable.

The increase in wildfire frequency worldwide has contributed to persistent atmospheric black carbon (BC) pollution, which was closely relative to multiple adverse health effects. Accurate quantification of BC in biological tissues and fluids is fundamental for evaluating its health effect; however, existing analytical methodologies are hindered by time-consuming protocols, low throughput, and the need for expensive instrumental infrastructure. In this study, we developed a fluorometric method for quantifying BC in various biological fluids with the advantages of simplicity, high sensitivity, and low cost. Specifically, this technique enables quantification of five distinct types of BC across diverse biological liquids with a detection limit (LOD) of 0.23-7.57 mg/L. The method's LOD is comparable to the established advanced techniques for BC quantification (e.g., femtosecond illumination technique and laser desorption/ionization mass spectrometry) but avoids the use of expensive instruments. Compared with conventional ultraviolet-visible (UV-Vis) spectrophotometry, the fluorometric technique demonstrates higher accuracy and less interference from proteins, water-soluble ions, or suspended particles. The practicability of the method was examined through the A549 cell-based toxicological assays. The biologically effective exposure dose (BED, a parameter for evaluating the actual exposure dose of chemicals) of BC to A549 cells was determined to be approximately 30 pg/cell, which overcame a fundamental measurement challenge regarding the BED of BC in cellular assays. Overall, the present method addresses a significant challenge in BC analysis, thus facilitating its accurate risk assessment.

Continuous monitoring of cerebral blood flow (CBF) with high spatiotemporal resolution and depth sensitivity is essential for accurate diagnosis and effective management of neurological disorders. Although conventional laser speckle contrast imaging (LSCI) enables widefield, high-resolution CBF mapping, its limited penetration depth and signal integration across all tissue layers hinder depth-resolved imaging. To address these limitations, we developed an advanced time-resolved LSCI (TR-LSCI) system that employs picosecond-pulsed laser illumination and a customized SPAD5122 camera operating in gated mode, enabling noncontact, widefield, and depth-sensitive CBF imaging. However, photon scattering and diffusive noise still degrade image quality, particularly at greater depths. To overcome this challenge, we incorporated a multiscale latent diffusion model (LTDiff++) into the TR-LSCI analysis pipeline to suppress photon diffusion noise. Trained and validated using overlapping image patches from head-simulating phantoms and neonatal rat CBF images with high-quality ground truth references, LTDiff++ effectively suppressed photon diffusion noise while preserving structural and vascular features at greater imaging depths. Moreover, in vivo studies demonstrated that LTDiff++ maintained image quality using only 5-frame averaging, reducing acquisition time by a factor of 20 compared to the conventional 100-frame averaging approach without deep learning enhancement. The integrated TR-LSCI and LTDiff++ framework thus enables robust, high-speed, and depth-resolved imaging of cerebral hemodynamics, offering a promising platform for preclinical research and future clinical applications in bedside neuroimaging and patient monitoring.

Evaluating safe infrared neural stimulation parameters: Calcium dynamics and excitotoxicity thresholds in dorsal root ganglia neurons.

MXene-loaded multifunctional nanoparticles with on-demand controlled antimicrobial and antioxidant capacity for multi-modal treating bacterial prostatitis.

Photoacoustic imaging (PAI) combines the high contrast of optical imaging with the high resolution of ultrasound imaging, which has garnered significant attention in applications such as vascular imaging and liver function reserve (LFR) assessment. The realization of low-cost and miniaturized light sources is a crucial development direction for the future application and commercialization of PAI. Traditional high-power pulsed lasers (hundreds of millijoules range) are bulky and expensive, although light-emitting diodes (LEDs) are lower in cost and more compact, their output energy is relatively weak (microjoules range), and their pulse width is wide (tens of nanoseconds range), making them unsuitable for high-resolution PAI of clinical application. This paper proposes a low-cost, compact PAI light source based on a miniature laser commonly used in laser communication and laser radar systems, combined with a second-harmonic generation (SHG) crystal. The primary diode pumped solid-state laser (DPSS) has the following specifications: dimensions of 110 × 40 × 24 mm3, weight of 220 g, operating wavelength of 1535 nm, single-pulse energy of 2.7 mJ (pulse stability is ±5%), pulse width of 10 ns, repetition rate of 5 Hz, and spot diameter of 0.8 mm (divergence angle is 4%). To meet the requirements of PAI, the nonlinear effect of a KTiOPO4 second-harmonic crystal is utilized, resulting in an output wavelength of 767.26 nm, pulse width of 10 ns, and single-pulse energy of 0.68 mJ. To verify this light source, we performed PAI of blood vessels in the human finger and dorsal hand, as well as PAI detection analysis with different concentrations of Indocyanine green (ICG). The results demonstrated that the proposed low-cost, compact second-harmonic laser has the potential for vascular imaging and LFR evaluation. The proposed method for the excitation source offers a reliable approach for the development of low-cost, compact PAI and contributes to the advancement of miniaturized, portable PAI systems.

Conventional top‐contact two dimensional (2D) Schottky photodetectors suffer from light shadowing and contact damage, leading to Fermi‐level pinning and performance degradation. This work overcomes these limitations by designing a bottom‐electrode Schottky photodetector (BE‐Schottky PD) based on a Cr/WSe2/Au heterostructure. The key innovation involves fabricating the bottom Schottky Cr electrode into pre‐etched SiO2 substrate trenches, making it flush with the surface. This unique geometry eliminates optical shadowing to maximize light absorption, and enables a high‐quality van der Waals Cr/WSe2 interface, mitigating Fermi‐level pinning. Consequently, the device exhibits an outstanding rectification ratio of 1.07 × 104 and an ideality factor of 1.11 due to the strong built‐in electric field. It demonstrates excellent self‐powered operation within the visible spectrum. Under 532 nm laser illumination and zero bias, it achieves rapid photoresponse with a fall time of 3.8 µs. This work, utilizing industry‐compatible metals and a simple process, realizes a high‐performance photodetector, highlighting the significant potential of 2D materials for efficient, low‐power, and ultrasensitive optoelectronics.

Stagnating surface tension below boiling temperature during laser illumination

Pintle injectors are a type of coaxial injector for liquid propellant rocket engines, which have radial and axial flows impinging on each other for atomization and mixing. Previous studies have investigated the spray characteristics of pintle injectors, specifically the spray angle and droplet size. However, the macroscopic spray structure of pintle injectors has not been sufficiently observed. This study focuses on spray structures of a multi-slit type throttleable gas–liquid pintle injector using shadowgraphy and two-phase structured laser illumination planar imaging (2p-SLIPI). Cold flow experiments using air and water with pintle tips of various configurations under a throttling range of 20%–100% were conducted. Three-dimensional spray structures from a multi-slit type throttleable gas–liquid pintle injector were reconstructed by 2p-SLIPI tomography, and the tomographic uniformity index (UI) of each case was calculated from the Mie scattering intensity. Cross-sectional spray patterns of the pintle injector could be classified into three types. The experimental results showed that the spray angle is significantly related to the cross-sectional spray pattern and UI of the pintle injector. A recommended range of the spray angle from the perspective of the UI was proposed.