Continuous Wave Laser Irradiation Research Articles

Damage mechanism and protective performance of vanadium dioxide under continuous-Wave laser irradiation

Optical limiters reduce transmittance under increasing incident optical power and protect sensitive components against high-intensity illumination. Vanadium dioxide (VO2), which is known for its thermochromic properties, is a suitable material for fabricating optical limiters. However, research on its phase transition and damage mechanisms under continuous laser irradiation remains limited. In this study, the temperature-dependent optical constants that determine the performance of VO2 were obtained using the proposed dispersion calculation model. The phase transition behavior and damage mechanism of a single-layer VO2 optical limiter exposed to 1064-nm continuous laser irradiation were investigated. The results revealed that a higher laser power on the optical limiter triggered the partial oxidation of VO2 into V2O5 within the damaged region, thus causing the transmittance before and after the phase transition in the damaged area to be higher than that in the undamaged area. Utilizing the calculation model results, a performance-enhancing VO2-based Fabry–Pérot optical limiter was developed. It exhibited a higher transmittance and a lower reflectance than single-layer VO2 in the open state and a lower transmittance in the limiting state. These findings serve as valuable references for the further optimization of VO2-based optical limiters.

Photoluminescence of CaGa2S4: Nd, Yb compound at room temperature

In this paper, CaGa2S4:3%Nd,5%Yb; CaGa2S4:5%Yb; CaGa2S4:3%Nd compounds were synthesized, and their photoluminescence (PL) spectra, PL excitation (PLE) spectra and PL decay properties were studied at room temperature under one-photon and multi-photon excitation in a wide range of excitation intensities. The synthesis of the CaGa2S4 compound was carried out by a solid-phase reaction of a stoichiometric mixture of CaS and Ga2S3 powders in a quartz ampoule. Yb and Nd doping was carried out during the synthesis process using YbF3 and NdF3. PLE spectra were studied in the wavelength range from 250 to 850 nm, and PL spectra in the range of 400 - 1500 nm. It has been shown that after introducing Yb3+ ions into thiogallate crystals with Nd3+ ions, a new band near 488 nm is formed and the PL intensity increases by 1-2 orders of magnitude. The anti-Stokes PL spectra of CaGa2S4: Nd, Yb crystals in the visible region of the spectrum (400–700 nm) were studied when excited by continuous wave laser radiation with a wavelength of 975 nm. The kinetics of PL decay of all types of compounds at different wavelengths of single- and multi-photon excitation were determined. Depending on the PLE conditions, wavelength and intensity of the exciting radiation, monoexponential and non-monoexponential decay kinetics were observed with decay times in the range of 20 – 90 μs. Possible mechanisms of PLE and PL of CaGa2S4 crystals doped with neodymium and ytterbium ions are discussed.

All-Optical Domain Inversion in LiNbO3 Crystals by Visible Continuous-Wave Laser Irradiation.

LiNbO3 is a distinguished multifunctional material where ferroelectric domain engineering is of paramount importance. This degree of freedom of the spontaneous polarization remarkably enhances the applicability of LiNbO3, for instance, in photonics. In this work, we report the first method for all-optical domain inversion of LiNbO3 crystals using continuous-wave visible light. While we focus mainly on iron-doped LiNbO3, the applicability of the method is also showcased in undoped congruent LiNbO3. The technique is simple, cheap, and readily accessible. It relies on ubiquitous elements: a light source with low/moderate intensity, basic optics, and a conductive surrounding medium, e.g., water. Light-induced domain inversion is unequivocally demonstrated and characterized by combination of several experimental techniques: selective chemical etching, surface topography profilometry, pyroelectric trapping of charged microparticles, scanning electron microscopy, and 3D Čerenkov microscopy. The influence of light intensity, exposure time, laser spot size, and surrounding medium is thoroughly studied. To explain all-optical domain inversion, we propose a novel physical mechanism based on an anomalous interplay between the bulk photovoltaic effect and external electrostatic screening. Overall, our all-optical method offers straightforward implementation of LiNbO3 ferroelectric domain engineering, potentially sparking new research endeavors aimed at novel optoelectronic applications of photovoltaic LiNbO3 platforms.

Study on heat and mass transfer characteristics of porous media with different pore structures under continuous wave laser irradiation

The pore structure determined by porosity and particle size will directly affect the remediation efficiency of thermal treatment on contaminated soil. To investigate the remediation capability of continuous wave laser soil remediation technology on soils with different pore structures, this paper establishes a heat and mass transfer model within unsaturated porous media under laser irradiation. Four pore structures were simulated, and the model’s reliability was experimentally validated. Under laser irradiation, energy exchange between the solid and gas phases has a minimal effect on the solid phase temperature. The temperature distribution of the solid phase in the four samples is similar, with the differences primarily arising from moisture content. Interface energy exchange dominated the rise in the temperature of the gas. The intrinsic Nusselt numbers for the four samples were 3.5, 4.4, 4.9, and 6.2, respectively. Laser irradiation causes the Nusselt number to decrease over time, but the relative magnitudes of the Nusselt numbers for the four samples remain unchanged. From the perspective of solid phase temperature, the capability of laser remediation for soils with different pore structures is similar. From the standpoint of gas temperature, the Nusselt number is decisive. However, considering the complex coupling relationship between gas temperature rise and Darcy velocity and evaporation rate, the influence of water saturation and intrinsic permeability cannot be ignored. The research findings can provide a theoretical basis and analytical methods for the efficient laser remediation of soils with different pore structures.

Ignition of Anthracite Microparticles by Continuous Wave Laser Radiation with Wavelengths of 450 and 808 nm

Ignition of Anthracite Microparticles by Continuous Wave Laser Radiation with Wavelengths of 450 and 808 nm

Laser ablation mechanism and performance of glass fiber-reinforced phenolic composites: An experimental study and dual-scale modelling

Both experimental and simulation approaches were employed to investigate the laser ablation mechanism and performances of Glass Fiber Reinforced Phenolic Composites (GFRP). During the ablation process, the difference in thermal conductivities of the glass fibers and the resin matrix as well as their discrepant physical and chemical reactions form a conical ablation morphology. The formation of a residual carbon layer effectively mitigates the ablation rate in the thickness direction. A higher power density results in a faster ablation rate, while a longer irradiation time leads to a larger ablation pit diameter. To account for the variation in thermal conductivity between the fiber and resin, a macro-mesoscale model was developed to differentiate the matrix from the fiber components. Finite element analysis revealed that laser irradiation leads to phenolic decomposition, glass fiber melting vaporization, and residual carbon skeleton evaporation. The dual-scale model exhibits precise prediction capabilities concerning the laser ablation process of GFRP, and its accuracy is confirmed through the comparison of simulation and experimental results for the GFRP laser ablation process. This model provides a feasible method for performance evaluation and lifetime prediction of GFRP subjected to continuous wave laser irradiation.

Highly Stable and Reversible Coloration of Oxide Nanoparticles Film by Ultrafast‐CW Laser Induced Band Engineering

AbstractColoration in oxides meets the challenge in achieving high stability and repeatability simultaneously. In this work, reversible coloration of TiO2 nanoparticles (NPs) film is demonstrated by alternate ultrafast (UF) laser and continuous wave (CW) laser irradiation. Under UF laser irradiation, oxygen vacancies are introduced in the TiO2 lattice, which lead to the bandgap reduction (2.73 to 1.50 eV) and surface blackening. The blackened area can achieve high resolution with size down to ≈1.1 µm. This coloration in TiO2 also shows excellent thermal stability that color fading is negligible even after thermal annealing at 700 K for 2 h in air. The generated high temperature by CW irradiation is known to be beneficial for the O2 dissociation on defected TiO2, thus promoting the internal oxygen diffusion to eliminate the vacancies. The energy band structure of TiO2 can be recovered accordingly, and decoloration is achieved. TiO2‐NPs film shows stable microstructures with barely changed optical properties after 12 cycles of coloration–decoloration process. This band engineering‐induced reversible coloration can also be applicable for broad oxides, e.g., ZnO, HfO2, and Ga2O3. Such highly stable and reversible coloration is promising in high‐performance micro/nano‐devices development for color display and optical encryption.

A stochastic multi-scale thermal conductivity numerical model for 2D C/SiC-Ti3SiC2 composite

Thermal conductivity and thermal response are the essential indexes of C/SiC composites in the thermal protection systems (TPS). A stochastic multi-scale finite element model is put forth for predicting the above parameters based on the microstructure characteristics of the plain woven (2D) C/SiC-Ti3SiC2 composite. The reliability of the proposed stochastic multi-scale model is verified by the experimental data of thermal conductivity as well as the temperature history obtained from the continuous-wave laser irradiation experiment. The effects of porosity, the carbon fiber and the Ti3SiC2 MAX phase volume fractions on thermal conductivity and temperature field are analyzed. The results show that the porosity significantly reduces the thermal conductivity and elevates the temperature. The mesoscale thermal conductivity rises with the increase of the Ti3SiC2 MAX phase. Increasing the volume fraction of Ti3SiC2 can decreases the temperature at the laser irradiation center zone. The study provides an efficient tool in the design of the thermal response of MAX phase-modified ceramic matrix composites.

A stochastic multi-scale thermal conductivity numerical model for 2D C/SiC-Ti3SiC2 composite

Thermal conductivity and thermal response are the essential indexes of C/SiC composites in the thermal protection systems (TPS). A stochastic multi-scale finite element model is put forth for predicting the above parameters based on the microstructure characteristics of the plain woven (2D) C/SiC-Ti3SiC2 composite. The reliability of the proposed stochastic multi-scale model is verified by the experimental data of thermal conductivity as well as the temperature history obtained from the continuous-wave laser irradiation experiment. The effects of porosity, the carbon fiber and the Ti3SiC2 MAX phase volume fractions on thermal conductivity and temperature field are analyzed. The results show that the porosity significantly reduces the thermal conductivity and elevates the temperature. The mesoscale thermal conductivity rises with the increase of the Ti3SiC2 MAX phase. Increasing the volume fraction of Ti3SiC2 can decreases the temperature at the laser irradiation center zone. The study provides an efficient tool in the design of the thermal response of MAX phase-modified ceramic matrix composites.

Laser-induced electro-response of oil shale: Principles and applications

This study introduces a laser-induced electro-response (LIER) method to address the challenges arising from the harsh detection environment and energy consumption in the conversion engineering of oil shale. LIER system with pulsed laser and continuous-wave laser was used to investigate the feasibility of oil yield detection and real-time pyrolysis characterization, respectively. The equivalent circuit model for oil shale measurement under the pulse laser irradiation was established, considering the laser-induced plasma and photoelectric effect. While the laser-induced thermal effect is the main cause of the LIER response of oil shale under continuous-wave laser irradiation. Due to the complex interactions between laser and oil shale, the LIER of oil shale is affected by many factors, such as external electric field, laser source type, laser wavelength, and laser energy or power. The external electric field can improve the responsivity of LIER. The LIER signal of oil shale strongly positively correlates with oil yield. Hence, the LIER evaluated oil yield more quickly without pyrolysis than traditional methods, which is helpful for the exploration for oil shale. In addition, the multi-stage LIER responses were monitored in real time during the combustion and pyrolysis processes of oil shale samples in air and N2 atmosphere, respectively, realizing an evaluation of the organic and mineral decomposition, which provides a supplementary approach to conventional chemical techniques. These results show that LIER has great significance for the precise evaluation and effective development of oil shale reservoirs, which will drive the advances in the exploration for oil shale.

Kerr coefficient and third-order nonlinear optical absorption coefficient of isotropic diacrylate mesogens at 632.8 nm wavelength

ABSTRACT Third-order optical nonlinearities of diacrylate mesogens RM82 and RM257 in the isotropic phase for a low-power continuous wave laser irradiation at 632.8 nm wavelength have been studied. In their isotropic state, the diacrylate mesogens exhibit quite large nonlinear absorption. We observe a large two-photon absorption coefficients, on an order of 10−6 m/W, for the mesogens. The Kerr coefficients of the mesogens are characterised using single beam Z-scan technique, and found to reach an order of 10−7 m/W. Both diacrylate mesogens exhibit a good material figure of merit.

Performance and compensation method of first-order liquid crystal beam-steering system under continuous wave laser irradiation

The effects of laser irradiation thermal deposition on the performance degradation of liquid crystal (LC) devices in high-power laser systems are extremely vital. In this study, the first-order beam-steering system (FBS) was developed using a passive liquid crystal polarization grating (LCPG) and liquid crystal adjustable wave-plate (LCAW). The LCPG was prepared by holographic exposure technology, and the LCAW was prepared using the standard LC cell preparation process. We investigated the influences of diffraction efficiency of FBS under a 1070-nm continuous-wave (CW) laser irradiation. The energy is concentrated in the −1st order at first. When the half-wave retardation was reached, all the energy is concentrated in the +1st order (∼97 %), and the beam is deflected. Once the phase retardation decreases below the half-wave retardation, the energy gradually reconcentrates in the −1st order. When the LCAW fails, the diffraction the energy is refocused to the −1st order by the LCPG. The results indicated that both thermal deposition and driving voltage reduce the phase retardation of the LCAW, generating a variation of energy between in ±1st orders. By reducing the driving voltage, this half-wave retardation can be recovered under a certain half-wave voltage and laser power density, and the diffraction efficiency of the +1st order can be compensated to ∼97 %. If the reduced phase retardation is not less than half-wave, the FBS can still be modulated in high-power continuous lasers. Our research provides a reference for the development of beam-steering technology based on LC materials in high-power laser systems.

Polymorphism and White Light Emission of 1‐Bromo‐3,5,7‐triphenyladamantane Compared with 1,3,5,7‐Tetraphenyladamantane

AbstractHere we report our investigation of 1‐bromo‐3,5,7‐triphenyladamantane (1) and the elucidation of polymorphic crystals (1 A and 1 B) using single crystal X‐ray diffraction. In the monoclinic crystal system of 1 A (P21/n), we observed CH–π interactions, while Br⋅⋅⋅Br interactions are absent. Conversely, the Br⋅⋅⋅Br interactions are an apparent factor in the formation of the monoclinic crystal system of 1 B (R ). We compare our findings with 1,3,5,7‐tetraphenyladamantane (2), characterized by numerous CH–π interactions in the solid. Computational analyses were employed to investigate the interactions within the characteristic dimers present in the unit cells of 1 A and 1 B, including visualization of noncovalent interactions and the use of the atoms‐in‐molecules approach as well as MO analyses. These support the notion of London dispersion (LD) dimer‐dimer interactions in 1 A between the phenyl moieties, whereas 1 B exhibits additional dimer‐dimer Br⋅⋅⋅Br contacts. In contrast, the crystals of 2 are exclusively held together by CH–π stacking LD interactions, a feature absent in the polymorphs of 1. Both polymorphic forms of 1 emit white light when subjected to 900 nm continuous wave laser irradiation, displaying a subtle blue shift compared to 2. The absence of CH–π stacking interactions between the dimers of 1 causes a small red‐shift in the emission spectrum.

Fundamental Origin of Si Surface Defects Caused by Laser Irradiation and Prevention of Suboxide Formation through High Density Ultrathin SiO2

This research investigates surface damage in electronic devices from laser irradiation, particularly focusing on voids, cracks, and vacancies. We discovered that applying a high-density ultrathin SiO2 layer effectively prevents such defects. Atomic Force Microscopy (AFM) analysis showed a significant reduction in surface roughness, with the Rq factor value dropping to 0.158 nm in samples coated with this SiO2 layer. Additionally, X-ray Photoelectron Spectroscopy (XPS) was used to study suboxide formation in the Al2O3/Si structure, revealing insights into defect origins. Electrical tests indicated a substantial decrease in laser-induced damage, evidenced by a leakage current density reduction to 2.4 × 10−6 A/cm2, markedly lower than uncoated samples. Post-metallization annealing (PMA) further improved results, with the interface state density decreasing to 0.63 × 1012 atoms eV−1 cm−2. Our findings highlight the effectiveness of the high-density ultrathin SiO2 layer in mitigating surface defects caused by continuous wave (CW) laser irradiation, promising significant advancements in electronic device manufacturing through potential application in CW laser annealing processes.

NaSr3Be3B3O9F4 crystal growth and continuous-wave laser generation at 266 nm

In this paper, we have grown a large NaSr3Be3B3O9F4 (NSBBF) crystal with a top-seeded solution method and generated a continuous-wave (cw) laser radiation at 266 nm with a Brewster-cut NSBBF. With a high-power cw 532 nm and a frequency doubling stage, up to 120 mW cw UV laser was generated at 266 nm. A high stability at 50 mW was obtained more than 10 h. This cw UV laser source is applicable for self-calibrating solar irradiators.

Fs Laser Patterning of Amorphous As2S3 Thin Films.

This study investigates the morphological changes induced by femtosecond (fs) laser pulses in arsenic trisulfide (As2S3) thin films and gold-arsenic trisulfide (Au\As2S3) heterostructures, grown by pulsed laser deposition (PLD). By means of a direct laser writing experimental setup, the films were systematically irradiated at various laser power and irradiation times to observe their effects on surface modifications. AFM was employed for morphological and topological characterization. Our results reveal a clear transition threshold between photoexpansion and photoevaporation phenomena under different femtosecond laser power regimes, occurring between 1 and 1.5 mW, irrespective of exposure time. Notably, the presence of a gold layer in the heterostructure minimally influenced this threshold. A maximum photoexpansion of 5.2% was obtained in As2S3 films, while the Au\As2S3 heterostructure exhibited a peak photoexpansion of 0.8%. The study also includes a comparative analysis of continuous-wave (cw) laser irradiation, confirming the efficiency of fs laser pulses in inducing photoexpansion effects.

Laser-assisted exfoliation of Ti3C2Tx.

As an emerging two-dimensional material, MXene has shown a wide range of applications, which has triggered the demand for efficient exfoliation of nanoflakes with large size and specific surface area. Here, we took advantage of the efficient photo-thermal conversion of Ti3C2Tx and employed 532 nm continuous wave laser irradiation to assist the traditional ultrasonic exfoliation, with no need for complex equipment and an expensive femtosecond or picosecond laser. This approach greatly improves the exfoliation efficiency, increases the size, uniformity and specific surface area of the Ti3C2Tx nanoflakes, and reduces energy consumption as well. The electrical conductivity of Ti3C2Tx film is also significantly enhanced (from 3135 to 7433 S m-1). It is demonstrated that the laser promotes the formation of Ti-OH and enhances the solubility of Ti3C2Tx in water, facilitating the exfoliation and preventing oxidation as a result.

Therapeutic potential of photobiomodulation on hydrogen peroxide‐induced oxidative damage in retinal pigment epithelial cells

Aims/Purpose: Photobiomodulation (PBM) is a cutting‐edge therapeutic method for restoring the functioning of injured mitochondria in experimental settings. Our goal was to find out how 780 nm PBM therapy affected the apoptosis and cell survival of hydrogen peroxide‐treated retinal pigment epithelial cells.Methods: After being treated with 150 μM hydrogen peroxide for 24 h, the retinal pigment epithelial (RPE) cells were exposed to continuous wave laser radiation with the following parameters: wavelength of 780 nm, power density of 140 mW/cm2, 65 mW/cm2 and 40 mW/cm2 and duration of 10 min and 30 min. Furthermore, light therapy was given to untreated control cells to check PBM effect on healthy group. After PBM therapy in a time‐dependent manner, cell survival and apoptosis were assessed by MTT assay and Annexin V/PI staining, respectively.Results: Based on MTT findings, PBM showed no obvious effect on cell viability in H2O2‐treated RPE cells, while after 48 h post‐PBM incubation, cell viability was dramatically improved. It was significantly increased at the power density of 140 mW/cm2 for 30 min application without unacceptable effect on control cells. RPE apoptosis was strikingly decreased in post‐PBM incubation group compared to H2O2‐treated group in a time‐dependent manner, as detected by flow cytometry.Conclusions: As a result, photobiomodulation supported its potential utility in the prevention and treatment of retinal disorders associated with oxidative stress by promoting cell survival and reducing apoptosis under oxidative stress.

Visualization of photothermal therapy by semiconducting polymer dots mediated photoacoustic detection in NIR II

Visualization of photothermal therapy mediated by photothermal transduction agents (PTAs) is important to promote individual treatment of patients with low side effects. Photoacoustic detection has emerged as a promising noninvasive method for the visualization of PTAs distribution but still has limitations in temperature measurement, including poor measurement accuracy and low tissue penetration depth. In this study, we developed biocompatible semiconducting polymer dots (SPD) for in situ coupling of photothermal and photoacoustic detection in the near-infrared II window. SPD has dual photostability under pulsed laser and continuous-wave laser irradiation with a photothermal conversion efficiency of 42.77%. Meanwhile, a strong correlation between the photoacoustic signal and the actual temperature of SPD can be observed. The standard deviation of SPD-mediated photoacoustic thermometry can reach 0.13 °C when the penetration depth of gelatin phantom is 9.49 mm. Preliminary experimental results in vivo show that SPD-mediated photoacoustic signal has a high signal-to-noise ratio, as well as good performance in temperature response and tumor enrichment. Such a study not only offers a new nanomaterial for the visualization of photothermal therapy but will also promote the theranostic platform for clinical applications.

Thermal-Induced Convective Flow around Core–Shell Gold Nanodimers under Continuous-Wave Laser Irradiation: Implications for Nanofluidics

Thermal-Induced Convective Flow around Core–Shell Gold Nanodimers under Continuous-Wave Laser Irradiation: Implications for Nanofluidics