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Thermoreflectance-based measurement of facet optical absorption in high power diode lasers
摘要： Severe heating due to partial absorption of outcoupled emission at the facet of a high-power diode laser can lead to catastrophic optical damage. The degree of absorption and subsequent heating at the facet is a function of the emission wavelength, the absorption properties of facet coatings and passivation layers, and the age of the device. The ability to quantify facet absorption is an essential step toward improving the reliability and maximum output power of diode laser systems. In this work, we have developed a technique to measure facet absorption in diode lasers using a combination of facet thermoreflectance imaging and a heat transport model. The approach can be used for a wide range of both coated and uncoated diode lasers.
关键词： catastrophic optical damage,diode lasers,optical absorption,thermoreflectance
更新于2025-09-12 10:27:22
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Impact of Proton and Electron Irradiation-Induced Defects on the Dark Current of GaAs Solar Cells
摘要： The same amount of non-ionizing energy is deposited in GaAs solar cells through 1 MeV proton and electron radiation at specific fluence values. The defects created are detected and characterized via temperature-dependent dark I–V analysis, and the energy levels are correlated to trap states observed via admittance spectroscopy. A remarkable difference is observed between the defect energy levels introduced in the proton and electron cases: in the former, the recombination centers lie around the mid-gap position, while in the latter they are spread over a wider energy range in the band-gap. This induces a profound difference in the degradation of the recombination current in the space-charge region. On the other hand, the degradation of the diffusion current in the neutral regions is found to be determined by the recombination velocities at the back and front hetero-interfaces of the solar cell. They depend only on the displacement damage dose and are independent of the particle type.
关键词： recombination current,semiconductor device modeling,surface recombination,Displacement damage,irradiation-induced defect,GaAs solar cell
更新于2025-09-12 10:27:22
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High-Power Large-Energy Raman Soliton Generations Within a Mode-Locked Yb-Doped Fiber Laser Based on High-Damage-Threshold CVD-MoS2 as Modulator
摘要： In our work, based on a high-damage-threshold MoS2 saturable absorber (SA), high-power intra-cavity Raman solitons within a passively mode-locked Yb-doped fiber laser were demonstrated successfully for the first time. The damage threshold of the MoS2 SA was as high as ~0.48 J/cm2. By adjusting the polarization states, stable single- or dual-pulse Raman soliton operations were obtained. The maximum average output power for single-pulse and dual-pulse Raman soliton operations was 80.11 and 89.33 mW, respectively. Our experiment results show significant enhancement in comparison with previous works, which provides fundamental guidance for future designs of high-power, large-energy, intra-cavity Raman soliton generations based on two-dimensional materials as SAs.
关键词： mode-locked Raman fiber laser,high-damage 2D MoS2 materials,ultra-fast optical modulation
更新于2025-09-12 10:27:22
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Thermal-stress distribution and damage characteristics of three-junction GaAs solar cell irradiated by continuous laser beam
摘要： According to the theory of Fourier heat transfer and thermal stress field, a model on thermal damage of three-junction GaAs solar cell is established. The temperature and thermal-stress distribution inside the solar cell, which irradiated by continuous laser, are calculated. Results show that the temperature and thermal-stress distribution are corresponded to the intensity distribution of the incident laser beam. The maximum values of the compressive and tensile stress increase with the increasing of the power density and waist radius of the incident laser. When the waist radius is 0.5 cm, the melting damage is the main damage pattern as the power density is below about 40 W/cm2. However, when the laser power density is higher the stress damage will change to the main damage form. As the waist radius increases, the change in damage processes will also occur at lower laser power density.
关键词： Three-junction GaAs solar cell,Thermal-stress,Continuous laser beam,Damage
更新于2025-09-12 10:27:22
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Knowledge-Based Identification and Damage Detection of Bridges Spanning Water via High-Spatial-Resolution Optical Remotely Sensed Imagery
摘要： Bridges over water are important artificial objects that can be damaged by natural disasters. Accurate identification and damage detection of such bridges through the use of high-spatial-resolution optical remotely sensed imagery are important in emergency rescue and lifeline safety assessment. In this study, we detail a knowledge-based method of identification and damage detection of bridges spanning water using high-spatial-resolution optical remotely sensed imagery. Data on the body of water are extracted to define spatial extent and improve the timeliness of identification and damage detection, the threshold values of the rectangle degree and area are set to remove false bridge targets, and the damaged parts are detected according to the bridge’s rectangular characteristics and the relationship with the body of water. First, the characteristics, such as spectral, geometric, and textural, and spatial relationships of the bridge over water, are analyzed. Second, to limit the spatial extent of bridge identification and improve computational efficiency, data on the body of water are extracted. Third, the post-event bridge is identified from the viewpoint of bridge integrity based on shape and area parameters. Damage detection is then performed according to the bridge’s integrity. Finally, the results are evaluated for both non-positional and positional accuracy. Results of experiments carried out in Huiyang and Wenchuan, China, show that the proposed method, using high-spatial-resolution optical remotely sensed imagery, is effective for identification and damage detection of fallen and collapsed bridges spanning water. Therefore, the method is useful in updating the geographic database of bridges and assessing damage to them caused by natural disasters.
关键词： Bridges spanning water,High-spatial-resolution optical remotely sensed imagery,Feature knowledge,Feature analysis,Identification and damage detection
更新于2025-09-12 10:27:22
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Surface structuring of Kapton polyimide with femtosecond and picosecond IR laser pulses
摘要： Pulsed laser ablation is one of the most efficient and clean methods for high-precision processing and modification of polymers and biomaterials. Polymer ablation has been extensively investigated with ultraviolet lasers while little attention has been given to the infrared (IR) region, which becomes particularly interesting with the recent advances in ultrashort laser technologies. Here, we report the results of a comparative study on 1030-nm ultrashort laser structuring of Kapton polyimide, a polymer important in a variety of applications, with direct comparison of 247-fs and 7-ps laser pulses. The laser-induced damage thresholds for both pulse durations have been determined and the femtosecond laser threshold has been found to be considerably lower than that for picosecond pulses (by a factor of ～ 3.5). Both femtosecond and picosecond laser–produced craters have been thoroughly investigated as a function of pulse energy and focusing conditions. It has been demonstrated that femtosecond laser pulses enable accurate polyimide structuring while picosecond irradiation regimes result in a number of undesired effects such as re-deposition of the ablation debris, surface swelling, and the formation of high rims around the ablation craters. The mechanisms of polyimide ablation with femtosecond and picosecond IR laser pulses are discussed.
关键词： crater profile,swelling,laser ablation,damage threshold,laser processing,ultrashort laser pulses,multiphoton absorption,polymers,polyimide
更新于2025-09-12 10:27:22
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Picosecond laser lift-off method for fracture and debonding of copper oxide layer grown on copper substrate
摘要： The objective of this work is to investigate the ablative removal behavior of copper oxide under the picosecond laser ( pulse duration 12 ps and wavelength 1064 nm) irradiation. For this purpose, a thin CuO layer with a thickness of about 750 nm is synthesized on a pure copper substrate by the dipping method to serve as the target samples for experimental tests. It is shown that, unlike the pure ablation behavior, the removal process of the CuO layer is mainly based on the nonthermal lift-o? e?ect, by which the stripping of the whole piece of oxide ?lms from the substrate can be achieved with a single pulse shot. A minimum ?uence required for peeling o? the layer is determined to be about 0.11 J/cm2. Further analyses demonstrate that the entire pop-o? of the CuO layer caused by the con?ned ablation at the interface occurs only if the laser ?uences are applied below 0.62 J/cm2. However, when it comes to the cases at higher ?uences, a thin residual layer can be observed remaining on the substrate. To explain this phenomenon, a plausible interpretation with respect to the ablation induced by nonlinear absorption and impact ionization is proposed, which declares that it is the combination of direct ablation and the interface lift-o? that ultimately causes such special removal features. In addition, the in?uence of the oxide ?lm thickness on the debonding threshold and the removal behavior are additionally assessed.
关键词： lift-off effect,damage threshold,thin oxide ?lms,laser selective removal
更新于2025-09-12 10:27:22
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Quercetin encapsulated biodegradable plasmonic nanoparticles for photothermal therapy of hepatocellular carcinoma cells
摘要： Photothermal therapy (PTT) is emerging as an effective treatment modality for cancer due to its non-invasive nature. However, the pro-inflammatory necrotic cell death during PTT limits its successful clinical application. Here, we have developed quercetin (QE) loaded biodegradable plasmonic nanoparticles that can specifically induce apoptosis in cancer cells after PTT. We have synthesized gold-coated liposome (LiposAu) and QE loaded gold-coated liposome (QE-LiposAu) nanoparticles by in situ reduction of chloroauric acid with ascorbic acid in the presence of bare liposomes (Lipos) or QE loaded liposomes (QE-Lipos), respectively. The gold coating was confirmed by transmission electron microscopic analysis, dynamic light scattering, and zeta potential measurements. LiposAu and QE-LiposAu nanoparticles showed a similar level of temperature rise upon 750 nm near-infrared (NIR) laser (650 mW, 3 W cm-2) irradiation. The photothermal conversion efficiency of QE-LiposAu nanoparticles was determined to be ~75%. The efficacy of PTT was found to be dependent on the internalization efficiency of LiposAu nanoparticles in cancer cells. Importantly, QE-LiposAu nanoparticles showed increased PTT efficacy over LiposAu nanoparticles in hepatocellular carcinoma cells (Huh-7). Moreover, QE-LiposAu nanoparticles induced apoptosis-mediated cell death after the PTT, and the extent of apoptosis was significantly higher than the LiposAu nanoparticles in Huh-7 cells. Further, QE-LiposAu nanoparticles-mediated PTT depolymerized microtubules network, suppressed Hsp70 expression, and caused DNA damage. QE-LiposAu nanoparticles were also found to be hemocompatible. The results together suggested that biodegradable QE-LiposAu nanoparticles are promising photothermal agents for cancer therapy.
关键词： heat shock protein,liposome,microtubule,apoptosis,gold nanoparticles,DNA damage,Photothermal therapy
更新于2025-09-12 10:27:22
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Single-Shot Multi-Stage Damage and Ablation of Silicon by Femtosecond Mid-infrared Laser Pulses
摘要： Although ultrafast laser materials processing has advanced at a breakneck pace over the last two decades, most applications have been developed with laser pulses at near-IR or visible wavelengths. Recent progress in mid-infrared (MiR) femtosecond laser source development may create novel capabilities for material processing. This is because, at high intensities required for such processing, wavelength tuning to longer wavelengths opens the pathway to a special regime of laser-solid interactions. Under these conditions, due to the λ2 scaling, the ponderomotive energy of laser-driven electrons may significantly exceed photon energy, band gap and electron affinity and can dominantly drive absorption, resulting in a paradigm shift in the traditional concepts of ultrafast laser-solid interactions. Irreversible high-intensity ultrafast MIR laser-solid interactions are of primary interest in this connection, but they have not been systematically studied so far. To address this fundamental gap, we performed a detailed experimental investigation of high-intensity ultrafast modifications of silicon by single femtosecond MiR pulses (λ = 2.7–4.2 μm). Ultrafast melting, interaction with silicon-oxide surface layer, and ablation of the oxide and crystal surfaces were ex-situ characterized by scanning electron, atomic-force, and transmission electron microscopy combined with focused ion-beam milling, electron diffractometry, and μ-Raman spectroscopy. Laser induced damage and ablation thresholds were measured as functions of laser wavelength. The traditional theoretical models did not reproduce the wavelength scaling of the damage thresholds. To address the disagreement, we discuss possible novel pathways of energy deposition driven by the ponderomotive energy and field effects characteristic of the MIR wavelength regime.
关键词： ultrafast laser,ablation,silicon,damage threshold,mid-infrared
更新于2025-09-12 10:27:22
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Influence of multiple laser impacts on thin leading edges of turbine blade
摘要： Laser shock peening is a mechanical surface improvement treatment used to enhance the fatigue life of critical components. This paper investigates the influence of multiple square laser impacts to study their special effect on the diverse mechanical behaviours of the thin leading edge surface of turbine blades. Most works existing in the literature have presented experimental investigations. The originality of our paper is to validate and numerically simulate the proposed model. Indeed, a 3D finite element method of a thin leading edge specimen, Ti–6Al–4V, of a turbine blade is numerically simulated using the ABAQUS software. The mechanical surface modifications (residual stresses, equivalent plastic strains and Johnson–Cook superficial damage) induced by the multiple square laser impact are examined in detail. The main purpose of this investigation is to determine the effects of single-sided and double-sided laser shock peening.
关键词： turbine blade,thin leading edge,Ti–6Al–4V,multiple square laser impacts,finite element method,equivalent plastic strain,Laser shock peening,Johnson–Cook superficial damage,compressive residual stress
更新于2025-09-12 10:27:22