Development of flame frequency stabilized-continuous wave laser excited atomic fluorescence spectrometric (flame-cw-LEAFS) technique and its applications for ultra-trace level determination of rubidium in spodumene.

Chirp-modulated light-induced thermoelastic spectroscopy for simultaneous precise measurement of resonant frequency and gas concentration.

Updating digital twin in supervisory control and data acquisition for sustainable laser beam micro machining

Laser beam welding of NiTi shape memory alloy sheets: Microstructural evolution and mechanical properties

Metal transfer behavior and its correlation with process parameters in coaxial wire laser directed energy deposition using an annular laser beam

Study on microstructure evolution and mechanical properties weakening mechanism of thick-plate Ti6321 titanium alloy fabricated by high-power vacuum laser beam welding

Mechanical and corrosion behavior of oscillating laser beam welded 2507 super duplex stainless steel: Synergistic effects of acidic seawater and strain states

Orbital angular momentum laser beams have many important practical applications, such as optical tweezers or ultrafast communications. Creating such beams represents an important challenge in photonics. Here, we demonstrate that torons, which are topological defects in liquid crystal textures, when embedded in a microcavity, generate a real-space non-Abelian gauge field responsible for the topological inversion of ground and excited states. The resulting ground state produces robust lasing with nonzero orbital angular momentum in each of the circular polarization components.

ConspectusThe growing demand for nanoscale temperature measurement capabilities is motivated by diverse applications such as thermal management of microelectronics and batteries, design of plasmonic systems, mechanistic studies of catalysis, and unraveling intracellular processes. Upconverting nanoparticles (UCNPs) are lanthanide-doped inorganic probes that are popular luminescent thermometers, with advantages including well-understood temperature-dependent behavior, broadly tunable excitation and emission wavelengths, and exceptional thermal and chemical stability. Like other optical thermometry techniques, luminescence thermometry provides the desirable capability of remotely collecting the temperature-dependent signal from the far field. Conventional implementations of luminescence thermometry also share a major limitation of other optical thermometry techniques, namely, their diffraction limited spatial resolution. However, in contrast with other optical thermometry techniques, luminescence thermometry also creates an opportunity to leverage certain unique strategies for circumventing the diffraction limit.In this Account, we discuss our contributions to initiating or building on three major strategies for achieving UCNP thermometry beyond the diffraction limit. Some of these concepts originate from or have direct parallels in the realm of biological imaging, where optical imaging with spatial resolution below the diffraction limit has been a longstanding goal; conversely, others have no direct bioimaging analogy. Exciting an isolated single UCNP with a diffraction limited laser beam enables thermometry with subdiffraction limited spatial resolution governed by the UCNP size, although this approach is inherently restricted to measurements at a single spatial point. We begin by describing our efforts to extend single-UCNP measurements to smaller UCNP sizes and understand how their temperature-dependent emission can be influenced by external factors such as the excitation laser intensity or the surrounding optical environment, the latter of which is exemplified by an investigation of how single-UCNP emission is altered when the UCNPs are placed on various metallic substrates. Next, we show how the principles underlying single-UCNP thermometry can be expanded to sample multiple temperature points within a subdiffraction region by combining different UCNP compositions with spectrally orthogonal temperature-dependent luminescence. As a practical demonstration, we resolve a nearly 20 K temperature difference over a sub-110 nm distance originating from the steep temperature gradient near a laser-heated Ag nanodisk. Finally, we discuss our adaptation of UCNP-based stimulated emission depletion (STED) super-resolution imaging for super-resolution nanothermometry, combining temperature-dependent STED spectroscopy, self-assembled UCNP monolayer formation, and a detection scheme that enables practical scan times. STED nanothermometry can reveal a temperature gradient on a Joule-heated microstructure that is undetectable with analogous diffraction limited measurements, showcasing the power of this approach. We conclude with our perspective on the outlook for UCNP thermometry methods that circumvent the diffraction limit, highlighting both current research needs to further improve the measurement capabilities and strategies that could facilitate broader adoption of these emerging techniques.

Abstract Duplex stainless steels are often used in the maritime, nuclear, oil and gas, and process industries due to their combination of acceptable price, good corrosion resistance, high strength and good toughness. This paper uses additive manufacturing to build a bolt geometry with 2205 duplex and characterizes the material performance through Charpy impact toughness testing at -46 °C, tensile testing, x-ray tomography and microstructure examination using light optical and scanning electron microscopy. Two different deposition paths were compared, where one produced high-quality material, while the other produced both systematic lack of fusion and a higher porosity density. X-ray tomography was unable to detect lack of fusion. Both deposition paths satisfied typical requirements for mechanical properties. Solution annealing was necessary to produce acceptable Charpy impact toughness, and tensile properties were acceptable and comparable to those of forged bar material. A repeating pattern of sigma phase precipitation was observed in the as-built material, but the amount was limited and located close to the bolt edge, so it was removed by specimen machining. Despite being able to produce the bolt with additive manufacturing, this will not be implemented in the part production process since its cost was 6.6x higher than an equivalent bolt turned from bar stock.

The objective of this work is to study the laser quenching process of AISI P20 + S mould steel, focusing on improving surface hardness and wear resistance. AISI P20 + S steel was laser-quenched using temperatures of 1000°C and 1200°C, and laser beam overlap rates of 10% and 25%. The as-received and laser quenched steel was characterized by optical microscopy, scanning electron microscopy, and X-ray diffraction. After laser quenching, nanoindentation and pin-on-disk tests were performed to determine hardness profiles and assess wear resistance, respectively. The hardness at the surface more than doubled compared to the hardness of the untreated steel, confirming the formation of martensite. The 1000°C laser quenching resulted in a depth lower than 700μm, with a surface hardness close to 8 GPa. At 1200°C, the depth increased to nearly 1400μm, and the hardness reached 8-9 GPa, although the thicker oxide layer formed during the laser treatment led to an increase in the wear coefficient and volume. Due to the detachment of oxide layers, the main wear mechanism observed was adhesive. The work carried out confirmed the potential of laser quenching in the surface hardening of mould steels.

Nimonic C263, a nickel-based superalloy and has extensive application in the fabrication of high-performance components like casings and exhaust structures in gas turbines, automotive systems and aircraft engines. Conventional machining of this alloy is very challenging as it has high strength, poor thermal conductivity and strong chemical affinity with tool materials. In this research work, laser beam machining is used to machine Nimonic C263 sheets to analyze the influence of laser power (Watts), cutting speed (m/min), gas pressure (Bars) and focal position (mm) on the surface roughness (µm), kerf width (mm), kerf taper (°) and heat affected zone (µm). The outcome of these critical process parameters is evaluated terms of analysis of variance and meticulous scanning electron microscopy analysis on the machines surface. Technique for order of preference by similarity to ideal solution (TOPSIS) is used to combine multiple responses variables into a single response by determining the closeness coefficient and further optimized using a hybrid grasshopper optimization algorithm (GOA) (combined TOPSIS based GOA). A confirmatory experiment is carried out under optimized conditions showing an improvement of 4.84% in overall response, validating the effectiveness of the proposed hybrid approach.

Abstract We investigate experimentally the single-particle motion in water of silica colloidal beads half-coated with carbon under the action of a converging laser beam. The beads are self-propelled in this medium by means of self-thermophoresis resulting from local heating as a result of light absorption by their carbon cap. Within a certain laser power range, we find that these particles exhibit a quasi-two-dimensional active motion near a solid surface with stochastic rotational reversals when propelling themselves away from the region of maximum intensity, which leads to a stable trapping with oscillatory-like behavior inside the illuminated region. The orientation autocorrelation function of this type of confined active motion displays damped oscillations whose characteristic frequency increases with increasing propulsion speed, thus resulting in four regimes of translational motion depending on the observation timescale: thermal diffusion, ballistic motion, oscillatory behavior, and confinement. Our experimental findings are well described by a minimal phenomenological model that includes the nonlinear effect of a torque that reorients the particle toward the center of the optical confinement, which in combination with rotational diffusion gives rise to the observed orientational changes that allow their oscillatory trapping inside the light field. We also show that a similar active trapping mechanism emerges in the case of Janus colloidal rods, even though the periodicity is hindered by their three-dimensional rotation in the laser beam.

Abstract A laser welding process of dissimilar materials (Al-5754 and Mg-AZ31) in a lap configuration is investigated numerically in this study. A set of volume-averaged mass, momentum, and energy conservation equations is used to simulate the process, along with appropriate boundary conditions. The discretized set of governing equations based on the finite volume method (FVM) is then solved numerically using the SIMPLER algorithm, pressure-velocity coupling, and TDMA. It is observed that a laser welding process involves simultaneous melting, solidification, and remelting. The novelty of this study lies, therefore, in identifying these simultaneous phenomena during laser welding using the enthalpy update scheme. The predicted thermal investigation is validated initially with the existing experimental and numerical investigations. The progression of the associated transport phenomena is then presented elaborately through the observation of the weld pool and heat-affected zone (HAZ) at various laser powers. It has been found that a minimum of about 2500 W laser power is needed to weld a 2 mm thick Al-alloy sheet onto a Mg-alloy sheet in a lap configuration. It is also found that there is a limit to the laser application time when the laser beam is applied statically. The depth of the weld pool increases within this time limit, and further laser application does not increase the depth of the weld pool due to periodic remelting and solidification. Such a limit disappears at higher values of laser power, i.e., greater than 3000 W.

During laser processing, optimizing the cutting performance by adjusting the angle or off-axis displacement between the auxiliary gas flow and the laser beam is an effective approach to improving processing quality and efficiency. However, traditional electromechanical actuators suffer from inherent limitations in compactness and multi-degree-of-freedom cooperative control, which restrict their applicability in high-speed and high-precision laser cutting systems. To address these limitations, this paper presents a five-degree-of-freedom magnetic levitation actuator for laser cutting lens control and proposes a multi-degree-of-freedom cooperative control strategy based on backstepping control (BC) to cope with the system’s strong coupling, nonlinearity, and model uncertainty. First, a dynamic model of the actuator system is established, and a corresponding BC is designed. Subsequently, a centralized control framework is developed, and comparative simulations and experiments are carried out between the proposed BC and a conventional PID controller. The experimental results demonstrate that the proposed BC method outperforms the PID controller in terms of multi-degree-of-freedom cooperative control capability and dynamic response, thereby significantly enhancing the overall control performance of the system.

Comprehensive strategies for defect mitigation and process optimisation in laser beam welding of aluminium alloys: a systematic review

Reverse canonical energy flow at the sharp focus of vector laser beams

Abstract In this study, we derive an analytical expression for the cross-spectral density (CSD) matrix elements of a phase-locked, partially coherent, radial astigmatic flat-topped array laser beam propagating through weak oceanic turbulence. This is achieved using the extended Huygens–Fresnel principle and the unified theory of coherence and polarization. The propagation characteristics of normalized average intensity distribution and mean-squared beam width are investigated in detail using the CSD matrix. Simulations consider the effects of key oceanic turbulence parameters, source beam properties, and the astigmatic coefficient. The results indicate that increasing turbulence strength causes beamlet broadening, with asymmetric trends in the x- and y-directions due to astigmatism. This behavior facilitates a more rapid evolution of the array beam into a Gaussian-like structure along the propagation path. Furthermore, increasing the beam flatness order and the spatial coherence length slows this transformation. Simulation and analytical findings are presented through illustrative graphs.

Abstract Laser cleaning of micro–nano particles is crucial for the maintenance of precision optical surfaces. This study explores a non-contact cleaning strategy that utilizes laser-induced water cavitation to remove CeO2 particles from the surface of K9 glass substrates. During the experiment, a 1064 nm, 12 ns pulsed laser beam was passed through the back of a transparent substrate to generate cavitation bubbles, which produced tangential shock waves when they collapsed. Experiments show that a laser energy of 180–240 mJ has a removal efficiency of over 90% with minimal substrate damage, and the surface morphology observed by scanning electron microscopy (SEM) indicates that there are rolling and sliding phenomena of particles. Research shows that the collapse of laser-induced cavitation bubbles generates strong tangential shock waves, causing the rolling removal of particles. Compared with the existing laser-based methods for removing micro–nano particles, it lowers the energy cleaning threshold and has a wider energy processing window. Furthermore, since this paper focuses on the particle cleaning of transparent substrates through the form of laser acting on the back and the laser energy used is relatively small, the damage caused to the front of the substrate is relatively small. The damage mainly comes from the rolling friction contact between the particles and the substrate.

This work focused on profiling the caustic and measuring the power of a handheld laser beam welding (HLBW) system. A Primes® FocusMonitor FM+ and PowerMonitor CPM-F-10 were used to characterize a Miller OptXTM 2 kW HLBW system. Spot size and power density are key process variables for laser beam welding. For HLBW, these variables are constantly subject to variations since they depend on the welder’s experience and the ability to maintain a steady torch position. In this context, accurate characterization of the laser beam becomes essential to HLBW procedures. Laser beam profiling routines were performed using four different beam powers, while the power was measured in the entire adjustable range. The beam exhibited a waist diameter of approximately 40 𝜇m, a Rayleigh length of 1.1 mm, and a divergence angle of 40.3 mrad. The average beam parameter product and M2 were 0.44 mm mrad and 1.3, respectively. The measured power output was consistently 4% above the nominal value across the entire power range. The results confirmed that beam geometry is sensitive to torch positioning due to the small spot size and short Rayleigh length. The proposed methodology yielded consistent results for beam characteristics and power output in HLBW systems.