High Laser Research Articles

Kilowatt high power ytterbium-doped fiber laser operation in a record wide temperature range from -50 ℃ to 50 ℃

Kilowatt high power ytterbium-doped fiber laser operation in a record wide temperature range from -50 ℃ to 50 ℃

Laser-Assisted Field Evaporation of Chromia with Deep Ultraviolet Laser Light.

In this work, samples of chromia (Cr2O3) scale have been prepared for atom probe tomography and field evaporated with deep ultraviolet laser light (258 nm wavelength). The investigated range of laser energies spans more than three orders of magnitude between 0.03 and 90 pJ. Furthermore, the effects of detection rate and temperature were investigated. Simultaneous voltage and laser pulses were employed on additional needle specimens to reduce the standing voltage and minimize background noise during the measurement. Smooth evaporation with minimal mass spectrum peak tails was maintained over the whole range of measurement parameters. High laser energies result in significant underestimation of the oxygen content. Only laser energies below 1 pJ resulted in measured values near the expected oxygen content of 60 at%, the closest being about 58 at%.

Study of the application of UAV and LiDAR to topographic survey of mountainous forest areas – Case study of Win 3 Wind Power Plant Project, Huong Hoa District, Quang Tri Province, Vietnam

Abstract Unmanned Aerial Vehicle (UAV) technology in conjunction with aerial photography and aerial Light Detection and Ranging (LiDAR) was used for topographic surveying of the Win 3 Wind Power Project area, a complex mountainous terrain situated in the Huong Hoa district of Quang Tri province, Vietnam with the primary objective to produce a map with a scale of 1:1,000 with a contour interval of 1.0 m, accompanied by 3D point clouds, a Digital Elevation Model (DEM), and an orthomosaic. Employing the UAV LiDAR system of DJI Matrice 300 RTK, we conduct ed survey flights, achieving a high point density laser scanning of 229 points/m2 and capturing ultra-high-resolution imagery at 4.22 cm/pixel. The integration of aerial LiDAR and photographic data results in a rich and detailed information repository regarding the surveyed terrain demonstrating that UAV LiDAR technology is a robust tool for geographic data collection, particularly in challenging terrain conditions in Vietnam. We also evaluated the accuracy of the created topographic map, achieving results that surpass the technical requirements and quality standards of the project. This underscores the potential and effectiveness of UAV LiDAR technology in the field of large-scale geographic data collection and mapping in Vietnam.

Spatter detection and tracking in high-speed video observations of laser powder bed fusion

Purpose In laser powder bed fusion (L-PBF) additive manufacturing, spatter particles are ejected from the melt pool and can be detrimental to material performance and powder recycling. Quantifying spatter generation with respect to processing conditions is a step toward mitigating spatter and better understanding the phenomenon. This paper reveals process insights of spatter phenomena by automatically annotating spatter particles in high-speed video observations using machine learning. Design/methodology/approach A high-speed camera was used to observe the L-PBF process while varying laser power, laser scan speed and scan strategy on a constant geometry on an EOSM290 using Ti-6Al-4V powder. Two separate convolutional neural networks were trained to segment and track spatter particles in captured high-speed videos for spatter characterization. Findings Spatter generation and ejection angle significantly differ between keyhole and conduction mode melting. High laser powers lead to large ejections at the beginning of scan lines. Slow and fast build rates produce more spatter than moderate build rates at constant energy density. Scan strategies with more scan vectors lead to more spatter. The presence of powder significantly increases the amount of spatter generated during the process. Originality/value With the ability to automatically annotate a large volume of high-speed video data sets with high accuracy, an experimental design of observed parameter changes reveals quantitively stark changes in spatter morphology that can aid process development to mitigate spatter occurrence and impacts on material performance.

Comparison of high intensity laser therapy and extracorporeal shock wave in treatment of lateral epicondylitis: a randomized controlled study.

This study aims to evaluate and compare the short-term efficacies of high-intensity laser therapy (HILT) and ESWT(focused) on pain, sensitivity, handgrip strength and functions, in the treatment of lateral epicondylitis (LE). Fourty seven patients (age range, 18 to 65 years) with unilateral elbow pain were randomized into two groups. HILT group (n = 24) and ESWT group(n = 23). The HILT and ESWT were administered three times a week for three weeks, and each treatment was combined with exercises. All paticipant in both of two groups were evaluated with ultrasonography for common extansor tendon thickness. A visual analog scale (VAS), quick Disabilities of the Arm, Shoulder, and Hand (QDASH), hand grip strength test were used to evaluate the patients before, one and six weeks after treatment. There were significant improvement in VAS, hand grip strength, QuickDASH scores and CET thickness before and after treatment in both group(p < 0,05). But there were no significant differences between the groups pre-treatment, at the 1st week, and 6th week after treatment (p > 0.05). Only hand grip strength was smilar to the pretreatment outcomes in HILT group. Both treatment methods were found to be effective and safe in the short-term treatment of LE. Consequently, these non-invasive, effective and safe techniques can be successfully used in the treatment of common pathology of the elbow.

Whispering Gallery Mode Micro/Nanolasers for Intracellular Probing at Single Cell Resolution.

Intracellular probing at single cell resolution is key to revealing the heterogeneity of cells, learning new cell subtypes and functions, understanding the pathophysiology of disease, and ensuring precise diagnosis and treatment. Despite the best efforts, an enormous challenge remains due to the very small size, extremely low content, and dynamic microenvironment of a single cell. Whispering gallery mode (WGM) micro/nanolasers (active WGM) offer unique advantages of small mode volume, high quality factors, bright and low threshold laser emission, and narrow line width, particularly suitable for integration within a single cell. In this review, we provide a focused overview of WGM micro/nanolasers for intracellular probing. We deliver information on WGM micro/nanolaser concepts, sensing mechanism, and biocompatibility, as well as recent progress in intracellular probing applications mainly covering cellular-level sensing, molecular-level detection, and feasibility for cellular imaging. At the end, challenges and prospects of WGM micro/nanolasers for intracellular applications are discussed.

Optical properties of carbon dots generated in liquid by pulsed IR laser at 1064 nm

Biocompatible carbon dots (CDs) have been synthesized by the laser ablation of graphite and vegetable carbon (charcoal) placed in a phosphate-buffered saline (PBS) solution. The carbon nanoparticles are produced by a pulsed IR laser beam, operating at 1064 nm, 100 mJ energy, and 3 ns pulse duration, interacting with the carbon matrix placed in the liquid at a 0.2 Hz repetition rate. The ablation rate, in terms of removed carbon mass per laser shot, was evaluated to be about 75.8 ng/pulse and 758 ng/pulse for graphite and charcoal, respectively. Optical and electronic microscopy, UV-Vis spectroscopy, and luminescence measurements were employed to evince the CDs dispersion through its photoluminescence emission. The UV excitation at a 365 nm wavelength induces CDs luminescence in the visible region, as a result of electron transition, at a wavelength band depending on the laser spot size, i.e., of the laser fluence. CDs luminescence emission obtained from charcoal is independent of the laser fluence, showing a major emission peak around 475 nm and a secondary emission peak at 515 nm. CDs luminescence emission obtained from graphite depends on the laser fluence, showing a minor wavelength band, around 474 nm, at high laser fluences and a major wavelength band, around 670 nm, at low laser fluence. The CDs luminescence of the produced biocompatible solution finds many applications in the bio-medical field, as will be presented and discussed.

Mamyshev oscillation self-starting mode-locked fiber laser based on a self-feedback amplifying sub-cavity.

The Mamyshev oscillator (MO) boasts unparalleled modulation depth advantages in establishing mode-locking. However, this also significantly inhibits the self-starting of mode-locking. This Letter addresses the issue by constructing a self-feedback mechanism for regenerative oscillation. By amplifying noise cycles during the initial pumping phase to introduce periodic fluctuations in light intensity, we successfully achieve self-starting mode-locking at 1550 nm in an MO with a single gain arm structure at the pump power threshold of 76 mW. This self-starting mode-locking mechanism based on self-feedback sub-cavity amplification demonstrates excellent stability and repeatability in a single-arm MO structure. It provides what we believe to be a new approach for developing simple, reliable, and high repetition rate mode-locked lasers.

High performance deep violet InGaN TQW laser diode through multi-layer thickness optimization using particle swarm optimization method

The paper details the optimization of efficiency parameters for a InGaN TQW laser diode using the particle swarm optimization algorithm through SILVACO software. By adjusting layer thickness based on output power, slope efficiency, and threshold current, significant enhancements were achieved. Three optimized laser diodes (LD1, LD2, LD3) were compared with a primary LD, revealing notable improvements in output power and overall performance. Analysis of carrier recombination rates in the active region highlighted increased stimulated recombination and decreased non-radiative recombination, particularly in the n-side well. The study also showed a more uniform radiative recombination in the quantum wells of the optimized LDs, especially in LD3. Investigation of electron and hole concentrations, current densities, and energy levels demonstrated higher electron and hole current density in the optimized LDs, with LD3 exhibiting substantial improvements over the primary LD. Notably, the optimized LDs displayed reduced threshold current and improved slope efficiency compared to the primary LD. The study identified optimal layer thicknesses based on various cost functions, resulting in significant enhancements in output power (0.561 W), slope efficiency (2.515 W/A), and reduced threshold current (less than 0.029 A), indicative of enhanced TQW laser diode performance. Overall, the research showcases the effectiveness of the particle swarm optimization approach in optimizing GaN-based TQW laser diodes, leading to improved efficiency characteristics and demonstrating the potential for enhanced performance in practical applications.

Laser power modulation between disturbed and undisturbed material removal regime in laser chemical processing

Laser chemical machining (LCM) is a method for removing material by thermally induced chemical dissolution of self-passivating metals. However, the process window is limited by disrupted material removal due to gas bubble formation and metallic salts and oxides deposition at higher energy input. Since the temperature increases, and therefore gas bubble growth takes time, it is hypothesized that the temporal modulation of laser power can remove the metal homogeneously, i.e., without disrupted material removal, while achieving a higher removal rate. Based on this, the dynamic process behavior of material removal is investigated for the LCM of titanium in phosphoric acid, using a rectangular modulation of the laser power with varying irradiation durations. As a result, however, high-speed videos show that gas bubbles are consistently generated, regardless of the applied laser power and power modulation, although the quantity of bubbles varies with different parameters. Even with short power durations (10 ms), the material deposition occurs after multiple irradiations. When the duration is longer, the material deposition increases in height along the laser scan direction. For the studied process parameters, a Fourier analysis in the spatial domain further indicates the correlation between the material removal frequencies and the modulation frequencies. In conclusion, the laser power modulation cannot prevent the disturbed material removal at high laser powers. Nevertheless, the material deposition can be utilized to generate periodic surface structures with a depth below and above the initial surface.

Manipulating photoluminescence properties of neodymium-doped fluorites through local structure regulation

The long upper level lifetimes are highly advantageous for laser diode pumped high energy laser systems. However, lifetimes of the rare earth neodymium ions, one of the most important active ions in 1 μm, are generally around 300 μs or less, which limits the development of laser diode pumped high energy lasers on neodymium gains. In this work, Nd:CaF2 and Nd:SrF2 were chosen and introduced with appropriate codopants to adjust the local structures, thereby modulating the coupling of active ions with the crystal fields. The transition rate was slowed down and a long lifetime nearly 600 μs was obtained. Neodymium-doped fluorites with broad emission bandwidths and high thermal conductivities are potential laser gains for generation of high repetition rate high power lasers.

Toward electron temperature profiles in hot-dense plasmas from x-ray spectral ensembles

High repetition rate laser systems enable new strategies for diagnosing plasma behavior with large datasets. Here, we define an ensemble technique that relies on randomized targeting of x-ray tracer micro-stripes. On each shot, a high-intensity laser pulse is focused on a solid target with Ti tracer stripes embedded in an Al foil, randomly targeting a micro-stripe, a portion of a stripe, or a gap between stripes. High-resolution, time-integrated x-ray spectrometers capture line emission from the portion of the micro-stripe that is heated to sufficiently high electron temperatures. Accumulation of many such cases is used to construct ensemble distributions of x-ray line intensities that encompass all relative offsets of the laser focus to the micro-stripe centers. Synthetic intensity distributions are likewise generated using collisional-radiative modeling. Bayesian fitting of modeled to measured intensity distributions establishes the most likely radial temperature profiles, enabling comparison to hydrodynamic models and calling into question the cylindrical symmetry of these micro-stripe-embedded systems. Ensemble techniques have significant potential for high-energy-density plasma diagnostics, especially with the advent of high repetition rate experiments.

Solidification cracking susceptibility of alloy 718 during additive manufacturing and evaluating method

Although hot cracks frequently occur during metal additive manufacturing (AM), there are very few fundamental studies on the cracking behaviour and susceptibility. In this study, a horizontal tensile-type hot cracking test was investigated for evaluating the solidification cracking susceptibility of alloy 718 quantitatively during AM, particularly in laser powder bed fusion. The factors influencing the cracking susceptibility were also examined. The solidification cracking was reproduced by the melting of the AMed specimen with a tensile load under conditions of heat source simulating the AM process. The critical initial tensile stress for solidification crack initiation could apply as an evaluation index for cracking susceptibility. The critical initial stress decreased with increasing the laser power. A similar tendency was observed during the melting of the powders set on tiny groove for simulating AM process. The critical strain rate for solidification cracking (CST) was derived by a thermal elastic–plastic analysis using the critical initial stress measured experimentally. The CST at the laser power of 1125 W was higher than that of 1000 W for no crack condition. Therefore, high CST corresponding to penetration shape with high laser power induce to deteriorate the solidification cracking susceptibility.

Additive manufacturing of Fe–Mn–Al–C lightweight steel by laser powder bed fusion: The role of laser scanning speed on forming quality, microstructure and properties

The Fe–Mn–Al–C lightweight steels have attracted great attention in the military, aerospace, and automotive industries due to their high strength and lightweight design. Nevertheless, the excessive Mn and Al inclusions have led to poor formability and processability, which brings challenges to the manufacture of large size complex structural parts. In this study, the lightweight steel with a composition of Fe–Mn–Al–C was prepared by laser powder bed fusion for the first time, aimed at investigating the effects of laser scanning speed. The results show that different laser scanning speeds have significant effects on the process sensitivity of lightweight steel, and too low or too high laser scanning speeds may lead to suboptimal sample quality, increased porosity and surface roughness. At a scanning speed of 800 mm/s, the optimal conditions for the lowest porosity (0.03%) and surface roughness (Sa = 3.34 μm) are achieved, resulting in the highest quality of the formed products. Furthermore, an increase in scanning speed results in a reduction in grain size and an enhancement of dislocation strength. When the scanning speed is 800 mm/s, the significant enrichment of Ni–Mn phase helps to enhance the pinning ability of dislocations, while the precipitation of nanoscale small and dense κ-carbide optimizes the Orowan strengthening effect. As a result, dislocation movement is effectively impeded, leading to superior comprehensive mechanical properties of exceptional strength-plasticity matched with a tensile strength, yield strength, and elongation after fracture of 1125.2 MPa, 1019.8 MPa, and 41.9%, respectively.

Effect of Ce co-doping on radiation resistance behavior and laser performance of Er/Yb/Ce co-doped high-phosphorous polarization-maintaining silica fiber

Er/Yb/Ce co-doped high-phosphorus silica fiber core glasses with varying Ce2O3 concentrations were prepared and systematically studied. Based on this research, optimized Er/Yb/Ce co-doped high-phosphorus polarization-maintaining silica fibers were subsequently fabricated using the modified chemical vapor deposition (MCVD) technique and hole drilling method. The study confirmed that there is an optimal range of Ce doping concentrations for spectral performance, Ce doping effectively suppressing the formation of P-related defects during X-ray irradiation, and the dynamic valence state transformation of Ce3+/Ce4+ ions during irradiation enhanced the radiation-resistant properties, as demonstrated through radiation-induced absorption (RIA), electron paramagnetic resonance (EPR), and L3-edge X-ray absorption near edge structure (XANES) spectra. The homemade fiber, with optimized element concentrations, exhibited high laser efficiency comparable to commercial high-power fibers. Furthermore, the radiation-induced background loss of the fiber was 0.16 dB/m under 60 krad γ-rays at a low dose rate of 100 rad/h, and the radiation-induced gain variation (RIGV) was 0.019 dB/krad.

Two-Way Single-Photon Laser Time Transfer for High-Speed Moving Platforms

The two-way laser time transfer technology, based on single-photon detection, is among the techniques requiring the least weight and power consumption for ultra-long-distance clock synchronization. It holds promise as the most viable technology for high-accuracy inter-satellite clock synchronization, particularly for small satellites that are highly sensitive to weight and power consumption. In this study, we analyze laser time transfer in fast-moving platforms and find that not only does the relative motion speed between platforms significantly impact the clock offset measurement, but also the components of each platform’s relative motion velocity are critical. We introduce a lightweight scenario for laser time transfer, capable of achieving high-precision and high-accuracy interstellar clock offset measurements within a 5000 km range using high repetition rate microchip lasers and single-pixel single-photon detectors. With a speed accuracy of ±0.06 m/s, the precision of clock offset measurement surpasses 3 ps at full width at half maximum (FWHM), making it suitable for high-speed and high-precision clock synchronization between near-Earth satellites.

Transient opto-thermal simulation analysis and experimental validation of LERP systems

Abstract Solid-state technology has revolutionized the lighting industry. However, efficiency-droop-limited LEDs introduce constraints to the luminances achieved, and as a result, laser diodes (LDs) are replacing them in the remote phosphor setup. This introduces a new family of lighting solutions, laser-excited remote phosphor (LERP) systems, which can outperform cutting-edge LEDs. LERP systems however have not yet reached their full potential as the high intensity laser beam induces high temperatures within the phosphor material whose emission characteristics heavily depend on temperature. For this reason, a simulation framework has been developed that combines optical and thermal analysis in order to study and optimize these systems and derive their temperature thresholds for sustainable long-term usage. The focus here is on transient analysis, where the interplay between optical and thermal effects can be accounted for and the time dynamics of the system can be investigated. This enables the study of operation points near or at the thermal quenching regime. Furthermore, advanced material models have been developed in order to incorporate the temperature-dependence. The experimental validation of the model has shown that experimental and simulated results are in good agreement.

Magnetoplasmonic Triblock Nanorods for Collective Linear Dichroism.

Polarized light detection is crucial for advancements in optical imaging, positioning, and obstacle avoidance systems. While optical nanomaterials sensitive to polarization are well-established, the ability to align these materials remains a significant challenge. Here, we introduce Au-Fe3O4-Au triblock nanorods as a novel solution. Synthesized via a space-confined seeded growth method, these magnetoplasmonic nanocomposites uniquely combine the strong polarization capabilities of Au nanorods with the magnetic alignment properties of Fe3O4 nanorods. This architecture results in exceptional collective linear dichroism, achieving a polarization ratio of approximately 14 at the device level. Our nanorods exhibit high detection sensitivity and laser damage resistance, positioning them as a promising platform for developing advanced optical devices.

Laser surface alloying of Hastelloy X superalloy with Amdry 365 powder: Microstructural evolution and microhardness

Laser surface alloying is a surface modification technique that melts coat powder and substrate with high laser power density. This study aims to improve the properties of Hastelloy X, a Ni-based superalloy used for gas turbine components, by applying a NiCoCrAlY coating using laser surface alloying. The purpose of this study was to investigate the process parameters including laser scanning speed, laser power, and stand-off distance on the microstructure and microhardness of the alloying zones. The findings indicate that different microstructures were formed in different alloying zones such as cellular, columnar, and equiaxed. The results also revealed the presence of β and γ phases in the dendritic and interdendritic regions. The microhardness at the interface was higher than that of the other alloying areas due to the increased content of the Mo element. This study concluded that the properties of Hastelloy X can be improved by using NiCoCrAlY powder through a laser alloying process.

SbO(OH)2(IO3): The First Polar Sb5+-Iodate with a Strong Second-Harmonic Generation Response and a Wide Bandgap.

Widening the bandgaps while maintaining a strong second harmonic generation response has always been a research hotspot in the field of nonlinear optical iodate materials. A strategy involving covalent bonding is proposed that leverages the high valent later main group cation to construct iodates with predominantly covalent interactions. By using BiO(IO3) as a template, the first Sb5+-containing polar iodate, SbO(OH)2(IO3) is successfully isolated. The introduction of the two hydroxide anions led to the reduction of layered BiO(IO3) into 1D SbO(OH)2(IO3) in which two corner-sharing SbO4(OH)2 octahedra are further bridged by an iodate group. The covalently bonded [SbO(OH)2]+ chains and the optimal packing fashion of the asymmetric IO3 - groups generate a very strong second harmonic generation signal of 14 times that of KH2PO4. Furthermore, SbO(OH)2(IO3) exhibits a wide bandgap of 4.14eV and a high laser induced damage threshold [27.9 × AgGaS2, 0.2 × KH2PO4 (10ns, 10Hz)].