Continuous Wave Laser Irradiation Research Articles

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.

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.

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

Multiscale ablation mechanism and performance of 2.5D Si3N4 f/SiBN-CMCs under continuous-wave laser irradiation

Multiscale ablation mechanism and performance of 2.5D Si3N4 f/SiBN-CMCs under continuous-wave laser irradiation

Glancing angle deposition of helical manganese oxide nanostructures on the glass substrate and study the optical nonlinearity by Z-scan technique

Helical manganese oxide nanostructures have been deposited on glass substrate by glancing angle deposition along with electron-beam evaporation technique. X-ray diffraction analysis, FESEM images, and FTIR spectroscopy confirmed the successful growth of the nanostructured thin film. The surface morphology and roughness of the deposited helical manganese oxide thin film were considered using the 2-D and 3-D AFM images. The optical constants along axes a, b, and c have been calculated from the effective medium approximation of Bruggeman. The refractive indices were found to be equal for helical manganese oxide nanostructures along a- and b-axes and greater than the refractive index along c-axis at λ < 600 nm; while these results are reversed for wavelengths greater than 600 nm. The same variations were observed for the extinction coefficients. The Z-scan measurements under continuous-wave (CW) laser irradiation at 532 nm showed a positive sign for both the nonlinear absorption coefficient and nonlinear refractive index of nanostructured helical manganese oxide demonstrating the attendance of induced absorption process and self-defocusing phenomena, respectively. We computed a 3rd-order nonlinear optical susceptibility, χ(3), equal to 0.042 esu that suggests the glancing angle deposited helical manganese oxide nanostructures with a strong nonlinear optical response can be a good candidate to develop nanophotonic devices.

Energy aggregation properties of TiO2-silica composite aerogel under ultra-high-energy (7 kW·cm-2) continuous-wave laser irradiation

TiO2, a light-shielding agent for silica aerogels, is widely used in optical limiting and photocatalysis, but its application in high-energy lasers is extremely limited. We added TiO2 to silica aerogel in three different ways to get the best resistance to high energy laser. Through microstructure analysis and high energy laser irradiation test results, it is concluded that direct deposition of TiO2 nanoparticles can achieve the best laser resistance synergistic effect with silica aerogel. A thermal barrier temperature difference of 1275 °C was generated with a material thickness of 7.5 mm. Comparing the microscopic pore structure before and after high-energy laser irradiation, it was observed that the phase transition destruction of the TiO2–silica composite aerogel was completely different from that of pure silica aerogel. The TiO2–silica composite aerogel showed no signs of breakdown within 2 min of continuous-wave (CW) laser irradiation with power of 7 kW·cm-2. By changing the amount of TiO2 added, we also obtained the general trend of this synergistic effect, extended the mathematical model “maximum energy transfer radius (METR)”, and advanced the application of this material in the field of high energy laser protection.

Microwave-assisted hydrothermal synthesis of LaOF:Yb3+, Ho3+ nanorods with high thermoresponsive upconversion luminescence for thermometry

Non-contact thermometry based on upconversion luminescence from lanthanide-doped nanoparticles is the best choice when temperature probes with higher precision, accuracy, sensitivity, and spatial resolution are required. Here, LaOF:Yb3+,Ho3+ upconversion nanoparticles (UCNPs) were demonstrated to be thermometers with a high sensitivity and thermal stability within the temperature range of 303–673 K. Microwave-assisted hydrothermal synthesis was used to obtain these rod-shaped UCNPs with a trigonal crystal structure. LaOF:Yb3+,Ho3+ UCNPs displayed green emissions due to the thermally-coupled levels (5F4, 5S2) and red emissions from the Stark-split sublevels of the 5F5 energy level belonging to Ho3+ under 980 nm continuous-wave laser irradiation. The upconversion emission originating from these transitions were remarkably sensitive to the temperature variation. Their fluorescence intensity ratios were explored to evaluate their relative (SR) and absolute (SA) sensitivities. Optical heating induced by continuous laser irradiation was also examined to assess the degradation of the luminescence caused by laser exposure.

Ostensible Steady-State Molecular Cooling with Plasmonic Gold Nanoparticles.

The optical and chemical properties of plasmonic materials have sparked extensive research in exploring their applications in various areas such as photocatalysts, chemical sensors, and photonic devices. However, complicated plasmon-molecule interactions have posed substantial obstacles for the development of plasmonic material-based technologies. Quantifying plasmon-molecule energy transfer processes is a crucial step to understand the complex interplay between plasmonic materials and molecules. Here we report an anomalous steady-state reduction in the anti-Stokes to Stokes surface-enhanced Raman spectroscopy (SERS) scattering intensity ratio of aromatic thiols adsorbed on plasmonic gold nanoparticles under continuous-wave laser irradiation. The observed reduction of the scattering intensity ratio is closely related to the excitation wavelength, the surrounding media, and component of the plasmonic substrates used. Moreover, we observed a similar extent of scattering intensity ratio reduction with a range of aromatic thiols and under different external temperatures. Our discovery implies that there are either unexplained wavelength-dependent SERS outcoupling effects, or some unrecognized plasmon-molecule interactions which lead to a nanoscale plasmon refrigerator for molecules. This effect should be taken into consideration for the design of plasmonic catalysts and plasmonic photonic devices. Moreover, it could be useful for cooling large molecules under ambient conditions.

Instantaneous Ablation Behavior of Laminated CFRP by High-Power Continuous-Wave Laser Irradiation in Supersonic Wind Tunnel.

Experimental and numerical investigations of the instantaneous ablation behavior of laminated carbon fiber-reinforced polymer (CFRP) exposed to an intense continuous-wave (CW) laser in a supersonic wind tunnel are reported. We establish an in situ observation measurement in the experiments to examine the instantaneous ablation behavior. The surface recession depth is calculated by using the Particle Image Velocimetry (PIV) method, taking the ply angle of laminated CFRP as a reference. A coupled thermal-fluid-ablation numerical model incorporating mechanisms of oxidation, sublimation, and thermomechanical erosion is developed to solve the ablation-through problem of multilayer materials. The results show that the laser ablation depth is related to the laser power density, airflow velocity and airflow mode. Thermomechanical erosion is the primary ablation mechanism when the surface temperature is relatively low and the cavity flow mode is a closed cavity flow. When the surface temperature reaches the sublimation of carbon and the airflow mode is transformed to open cavity flow, sublimation plays a dominant role and the ablation rate of thermomechanical erosion gradually decreases.

Investigation of thermal damage in continuous wave laser-induced nanowelding

Continuous wave (CW) laser-induced nanowelding holds great promise in micro-and nano-devices. However, because of the lengthy irradiation duration, the heat effect from CW laser irradiation may harm the manufactured devices. The simulation results show that an increase in irradiation duration will slightly improve the welding temperature but greatly expand the heat-affected area when the irradiation time exceeds 100 ms. Experimental results confirm that Cu nanowires irradiated for 20 ms are slightly oxidized. As the irradiation period is increased to 10,000 ms, the oxygen concentration in Cu nanowires significantly increases, and the color of Cu nanowires becomes first black, then green. The electrical property of the oxidized Cu-Au nanojunction shifts from ohmic contact to Schottky contact. Furthermore, the large heat-affected area will weaken the adhesion between the Au pad and the substrate due to the large difference in thermal expansion coefficient between the metal film and the insulating layer. Consequently, CW laser-induced thermal damage not only impairs the electrical properties of nanostructures but also their reliability.