Laser Parameters Research Articles

Electromagnetically Induced Transparency Cooling of High-Nuclear-Spin Ions.

We report the electromagnetically induced transparency (EIT) cooling of ^{137}Ba^{+} ions with a nuclear spin of I=3/2, which are a good candidate of qubits for future large-scale trapped-ion quantum computing. EIT cooling of atoms or ions with a complex ground-state level structure is challenging due to the lack of an isolated Λ system, as the population can escape from the Λ system to reduce the cooling efficiency. We overcome this issue by leveraging an EIT pumping laser to repopulate the cooling subspace, ensuring continuous and effective EIT cooling. We cool the two radial modes of a single ^{137}Ba^{+} ion to average motional occupations of 0.08(5) and 0.15(7), respectively. Using the same laser parameters, we also cool all the ten radial modes of a five-ion chain to near their ground states. Our approach can be adapted to atomic species possessing similar level structures. It allows engineering of the EIT Fano-like spectrum, which can be useful for simultaneous cooling of modes across a wide frequency range, aiding in large-scale trapped-ion quantum information processing.

Laser hardening of aerospace structural materials

The work is devoted to the study of laser shock treatment of structural materials used in aviation and space technology with powerful nanosecond pulses in order to reduce surface damage, as well as resistance to crack growth. The hardening effect is achieved due to the mechanical deformation produced by the shock wave from the laser pulse due to the rapidly expanding plasma in the area of the irradiation spot. In this work, laser parameters for processing structural materials are calculated to ensure the required laser radiation power density. The results of laser processing with high-power nanosecond pulses of materials such as oxygen-free copper, aluminum alloy and germanium at various energy densities, with and without a protective coating and a water layer are shown.

Bayesian optimization of proton generation in terawatt laser–CH2 cluster interactions within a plasma channel

Improving the energy efficiency in generating high-energy proton or boron ions is crucial for advancing the feasibility of neutronless laser-based proton–boron (p-B11) fusion reactions. The primary objective of this work is to optimize the fusion energy efficiency of a proposed advanced p-B11 fusion scheme. In the proposed scheme, an ultrashort laser pulse is guided by a plasma channel filled with carbon–hydrogen (CH2) clusters. The MeV protons are generated by the Coulomb explosion (CE) of the cluster, which, therefore, interact with surrounding boron to produce alpha particles. To evaluate the fusion energy efficiency under various conditions, 2D particle-in-cell (PIC) simulations are used, supplemented with analytical calculations and estimations. The Bayesian optimization (BO) algorithm is utilized to optimize the key interaction parameters. The BO approach allows us to identify optimal cluster and laser parameters that would have higher fusion energy efficiency.

Interdependence of metal vapor plume and melt pool dynamics during laser beam welding under vacuum

Deep penetration laser beam welding involves the emission of hot metal vapor and particles from the keyhole, which interact with the laser beam by means of scattering, absorption, and phase front deformation. The combination of scattering and absorption leads to an extinction of the laser beam, while the phase front deformation adversely affects the beam quality. The capillary formation depends on the local distribution of the absorbed irradiance of the laser beam, which in turn is related to the material process emissions. Additionally, the process atmosphere, in particular the oxygen content, and the working pressure influence the capillary fluctuations and cause variations in welding penetration. This study introduces a measurement setup using simultaneous high-speed observation of the melt pool and the keyhole while measuring the interaction mechanisms between the laser beam and the metal vapor plume during laser beam welding under vacuum of stainless steel. The obtained measurement provides a quantification of the various interaction mechanisms between the laser beam, vapor plume, keyhole, and interdepended melt pool dynamics. These quantitative high-frequency measurements at various working pressures and laser parameters provide useful insights that are crucial for understanding the formation of weld defects, resulting in process monitoring and validation of process-oriented welding simulations.

Mild Fabrication of Polymeric Porous/Nonporous Micro‐Composite Structures via Enhancing the Photothermal Conversion of Ultrafast Laser

AbstractLocalized foaming of polymers is promising to fabricate polymeric composite structures for applications in biomedical, aerospace, automotive, etc. However, the severe pyrolysis and carbonization of polymer chains during localized foaming may degrade the bulk strength. Herein, a mild localized foaming strategy is proposed to fabricate poly(lactic acid) (PLA) micro‐foams within dense PLA matrices using ultrafast lasers. The PLA substrates doped with graphene (Gr) and azodicarbonamide (AC) are developed for mild foaming. A picosecond laser is applied to pattern PLA micro‐foams on the PLA/Gr/AC substrates to fabricate porous/nonporous micro‐composite structures. The thermal behavior of the PLA/Gr/AC substrates is characterized to evaluate their capability in photothermal conversion and mild foaming during ultrafast laser pulses. To optimize the laser foaming process, the microstructure of the laser‐foamed PLA processed with different laser parameters is studied. It demonstrates that the oxidation of the functional groups dominates the side reactions on the PLA chains with slight variation in molecular weight during laser foaming, indicating that the PLA chains keep almost intact and mild localized foaming is realized. Furthermore, the developed technology is demonstrated for micro‐patterning and texturing, material toughness programming, and shape memory programming, showing promising applications for smart materials, metamaterials, micro‐robotics, and biological scaffolds.

ULPING-Based Titanium Oxide as a New Cathode Material for Zn-Ion Batteries

The need for alternative energy storage options beyond lithium-ion batteries is critical due to their high costs, resource scarcity, and environmental concerns. Zinc-ion batteries offer a promising solution, given zinc’s abundance, cost effectiveness, and safety, particularly its compatibility with non-flammable aqueous electrolytes. In this study, the potential of laser-ablation-based titanium oxide as a novel cathode material for zinc-ion batteries was investigated. The ultra-short laser pulses for in situ nanostructure generation (ULPING) technique was employed to generate nanostructured titanium oxide. This laser ablation process produced highly porous nanostructures, enhancing the electrochemical performance of the electrodes. Zinc and titanium oxide samples were evaluated using two-electrode and three-electrode setups, with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge (GCD) techniques. Optimal cathode materials were identified in the Ti-5W (laser ablated twice) and Ti-10W (laser ablated ten times) samples, which demonstrated excellent charge capacity and energy density. The Ti-10W sample exhibited superior long-term performance due to its highly porous nanostructures, improving ion diffusion and electron transport. The potential of laser-ablated titanium oxide as a high-performance cathode material for zinc-ion batteries was highlighted, emphasizing the importance of further research to optimize laser parameters and enhance the stability and scalability of these electrodes.

Optimization of GeSn nanostructures via tuning of femtosecond laser parameters

Semiconductor nanostructures are known to exhibit interesting electrical and optical properties, as well as functionalities that are significantly different from their bulk counterparts. These unique characteristics can be attributed to their quantum confinement effects, and large surface-to-volume ratios, along with the fact that their compositions can be tuned. This study proposes a new method for tuning the properties of GeSn nanostructures on a silicon substrate using femtosecond laser direct writing. A series of GeSn nanostructures with different compositions of Sn ranging from nanodots, nanoholes, nanostrips, nanogaps, and nano-cauliflowers were successfully prepared via tuning of femtosecond laser parameters. The morphology, composition of Sn, and crystalline properties of the formed nanostructures were also greatly influenced by the laser fluence and the effective pulse number. The femtosecond laser/GeSn interaction mechanism was thoroughly investigated based on the two-temperature Drude model. This work provides a novel strategy for tuning the bandgap and morphology of GeSn nanostructures, through which the properties of GeSn-based devices can be tailored according to the requirements of practical applications in the fields of microelectronics and photonics.

Modeling nanogratings erasure at high repetition rate in commercial optical glasses

Volume nanogratings (NGs) imprinted by infrared femtosecond laser in commercial optical glasses take the form of orientable subwavelength birefringent nanostructures, being composed of an assembly of nanopores. The existence of NGs strongly depends on the laser parameters and glass composition. Therefore, in this work, we tentatively model the erasure threshold of NGs in a pulse energy - repetition rate processing window. For this purpose, we combine i) a heat diffusion model to simulate the thermal treatment experienced by the glass upon laser irradiation, and ii) the Rayleigh-Plesset equation to take into account the evolution of a nanopore size during laser processing. We first determine a criterion for nanopores erasure, falling within a typical characteristic time of few tens of ns, in which the cooling of the last laser pulse absorbed by the material is progressively cooled. Then, considering a multiple pulse regime and the dependence of the deposited pulse numbers on the thermal treatment, the modeled NGs erasure threshold follows the experimental trend. Finally, considering a steady state regime for various repetition rates, and adjusting the energy deposition (absorption coefficient or beam waist) as a function of the pulse energy, the NGs existence window can perfectly match the experimental values.

Focal point technology: Controlling treatment depth and pattern of skin injury by a novel highly focused laser

Selective photothermolysis has limitations in efficacy and safety for dermal targets. We describe a novel concept using scanned focused laser microbeams for precise control of dermal depth and pattern of injury, using a 1550nm laser that generates an array of conical thermal zones while minimizing injury to the epidermis. To characterize the conical thermal zones invivo and determine safe starting parameters to transition to a second phase to explore potential clinical indications. A focused toroidal (ring) laser beam was delivered through a cold sapphire window, sparing epidermal injury in a central zone. Pulse energy, lesion depth, density, and energy delivery were titrated in exvivo human skin and subsequently on the backs of 21 human subjects. Histology showed microscale patterns of thermal injury, which varied predictably with laser parameters. Time-course healing through histology and skin surface imaging demonstrated the ability of the device to deliver high energies without sequelae. Clinical data are currently being collected to further explore the safety and efficacy of the device. The 1550nm laser with focal point technology enables precise control of lesion depth while simultaneously sparing a large portion of the epidermis, lowering the risk of adverse effects.

Self-Trapping of a Laser Beam of Ultrarelativistic Intensities

Since a theory that can justify the condition of matching of the laser and plasma parameters to implement the relativistic self-trapping regime for laser light in a plasma, which is the most efficient for the acceleration of electrons, is still absent, doubts remain in the necessity of the corresponding extensive experimental studies, particularly in view of the lack of justification or completion of previous theories. The presented theoretical analytical approach, which includes the relativistic nonlinearity of the electron mass and electron cavitation in the plasma, allows one to overcome this problem and provides an analytical justification of the conditions of such matching for ultrarelativistic laser beams at the quantitative level, which is in agreement with the multidimensional numerical simulation.

Achieving fine tailoring of elastocaloric properties of laser powder bed-fused NiTi alloy via laser beam manipulation

Laser powder bed fusion (LPBF) technology enables the development of NiTi alloys with complex geometries and tunable phase-transformation temperatures (PTTs). This technology is increasingly acknowledged as promising in the field of elastocaloric (eC) refrigeration. However, the mechanisms governing the manner in which this technology tunes the eC performance remain ambiguous. This study evaluated the fine-tuning of the eC properties by regulating Ni evaporation through laser manipulation. Our results demonstrate that although adjusting Ni loss via laser heat input can effectively control the PTTs, inappropriate combinations of laser parameters may result in lower than anticipated cooling capacity (ΔTad) and coefficient of performance (COPmat) of produced samples. An excessive heat input results in Ni evaporation and in grain coarsening through the remelting and combination of fine grains owing to overlapping molten pools. Lower Ni enhances the phase-transformation enthalpy (ΔHtr). However, larger grains increase the energy dissipation and thereby, counteracting ΔTad improvements. Theoretical analysis and experiments revealed that finer grains increase the misorientation angles. This hinders the dislocation motion and thereby, enhances the mechanical properties. Meanwhile, coarser grains can more conveniently promote PT and thereby, increase ΔHtr. Thus, based on the naturally controllable grain size heterogeneity in LPBF-manufactured NiTi alloys, we propose optimizing the eC properties by controlling the morphology of the molten pool. Thermal-history simulations could balance this relationship. Ultimately, we developed two NiTi alloys for both high-temperature (70 °C) and room-temperature (25 °C) refrigeration. This study has provided effective insights for customizing high-performance eC components such as multistage caloric cascade regenerators, using additive manufacturing.

Efficiency of dry versus wet Er,Cr:YSGG laser debonding of lithium disilicate veneers using different power outputs

Since water is the chromophore for the erbium, chromium-yttrium scandium gallium garnet (Er,Cr:YSGG) laser, the laser energy reaching the restoration decreases as part of it is absorbed by water. Theoretically, reducing the water or implementing dry debonding could reduce the energy consumed by water, increasing laser efficiency. Studies on whether it is suitable for removing veneers without using coolant are lacking. The purpose of this in vitro study was to evaluate the debonding time, intrapulpal temperature, and translucency of veneers during wet versus dry debonding with an Er,Cr:YSGG laser using different power outputs. Sixty-three maxillary central incisors were flattened labially to receive ceramic specimens. After cementation, ceramic specimens were irradiated with an Er,Cr:YSGG laser for debonding with different power outputs and water percentages (N=70): subgroup A1, 4W and 1% water; A20, 4W and 20% water; A40, 4W and 40% water; B1, 5W and 1% water; B20, 5W and 20% water; B40, 5W and 40% water; C1, 6W and 1% water; C20, 6W and 20% water; C40, 6W and 40% water, and a control group of unbonded ceramic specimens. During debonding, the temperature rise and debonding time were evaluated, followed by the evaluation of the translucency and surface topography of the debonded specimens. Two-way analysis of variance (ANOVA) and the Dunnett test were used to analyze the data (α=.05). The mean intrapulpal temperature rise varied significantly among groups B and C (P<.001), with the highest mean temperature rise found in subgroup B1 (4.00 ±0.00 ºC) and the lowest mean temperature rise in subgroup C20 (1.20 ±0.45 ºC). For the debonding time, the mean values of time required for debonding varied significantly among different groups (P<.001), with the longest time recorded in subgroup A1 (333.4 ±74.8s) and the shortest time recorded in subgroup C20 (17.0 ±6.0s). Only subgroups C1 (18.89 ±0.2) and C40 (18.60 ±0.2) showed a significantly lower translucency than the control group (19.44 ±0.06) (P<.001). Dry Er,Cr:YSGG laser debonding resulted in increased intrapulpal temperature when using high power outputs, but without exceeding the critical threshold of dental pulp temperature. Dry debonding also limited the transmission of laser energy, affecting the debonding efficiency. A power output of 5W and 20% water can be considered efficient and safe laser parameters for debonding lithium disilicate veneers if their reuse is intended.

Random laser ablated tags for anticounterfeiting purposes and towards physically unclonable functions

Anticounterfeiting tags affixed to products offer a practical solution to combat counterfeiting. To be effective, these tags must be economical, capable of ultrafast production, mass-producible, easy to authenticate, and automatable. We present a universal laser ablation technique that rapidly generates intrinsic, randomly distributed craters (in under a second) on laser-sensitive materials using a nanosecond pulsed infrared laser. The laser and scanning line parameters are balanced to produce randomly distributed craters. The tag patterns demonstrate high randomness, which is analyzed using pattern recognition algorithms and root mean square error deviation. The optical image information of the tag is digitized with a fixed bit uniformity of 0.5 without employing any debiasing algorithm. The efficacy of tags for anticounterfeiting is presented by securing the challenge associated with each tag. Statistical NIST tests are successfully performed on responses generated from both single and multiple tags, demonstrating the true randomness of the sequence of binary digits. The single(multiple) tag(s) achieved an actual encoding capacity of approximately 10391 (10518) and a low false rate (both positive and negative) on the order of 10−58 (10−50). Our findings introduce a laser-based method for anticounterfeiting tag generation, allowing for ultrafast and straightforward product processing with minimal fabrication and tag cost.

The theoretical study of high-order dissipation soliton molecules evolution in a passively mode-locked fiber laser

High-order solitons represent a special form of soliton. Due to the complexity of their spatial structure and dynamic evolution, they have important applications in communication systems such as wavelength division multiplexing and secure communication. However, compared to traditional solitons, research on the spectral evolution of high-order solitons is still insufficient. In this paper, through precise control of laser parameters, the dynamic evolution process from stable dissipative single soliton to complex dissipative 8-order soliton molecules in passively mode-locked fiber lasers was successfully simulated. This demonstrates the complexity of solitons interaction and reveals the regularity of soliton molecules order with variations in four parameters: the small signal gain coefficient, nonlinear coefficient, gain bandwidth and the polarization controller angle. Through deep analysis of the order of soliton molecules, pulse shape and spectral shape of dissipative soliton molecules, we showcase the potential of fine-tuning laser parameters to achieve high-order dissipative soliton molecules. This work provides important references for the optimization design and expanded applications of lasers, further driving the development of high-performance, high-efficiency fiber laser technology.

High-powered 675-nm laser: Safety and efficacy in clinical evaluation and in vitro evidence for different skin disorders.

Laser technology is a viable therapeutic option for treating a number of skin pathologic conditions, including pigmented lesions, vascular lesions and acne scars. In this work, through in vitro and clinical investigationswe test the efficacy, the safety and the speed of treatment of high-powered laser system emitting a 675-nm in the management of various skin condition. In vitro experiments were performed irradiating adult human dermal fibroblasts cells (HDFa) with 675-nm laser for 24, 48 and 72h with different fluences and Ki-67+ cells were counted. The confocal microscopy images of control and treated samples were acquired. Clinical skin rejuvenation/diseases treatments with 675nm laser device were performed with different laser parameters in 11 patients with pigmented lesions, 5 patients with acne scars and 23 patients for skin rejuvenation. Data were evaluated with the validated global score using 5-point scales (GAIS) and patient's satisfaction scale. The application of the high-power 675nm laser has proven effective in stimulating cell proliferation in in vitro experiments and it led to good results for all skin pathologies. GAIS showed values between 3 and 4 points for all treated pathologies, all scores between '75%-good improvements' and '100%-excellent improvements'. The treatment time was reduced by 50% compared to the old parameters setting, resulting in a faster and good patient's satisfying technique. No serious adverse effects were recorded. the preclinical and clinical data confirm the efficacy and safety of this high-powered 675nm laser for several skin condition.

Research on the surface quality improvement of 3D-printed parts through laser surface treatment

This study investigates laser polishing as a post-processing technique to reduce surface roughness in ABS and Nylon parts produced via Fused Deposition Modeling (FDM). The research utilized CO2 and Nd:YAG lasers to polish these materials, achieving surface roughness reductions of 95.9 % and 96.0 % for CO2-treated ABS and Nylon samples, respectively, while Nd:YAG-treated samples exhibited reductions of 67.3 % and 68.6 %. Additionally, the study explores the impact of various laser parameters on surface quality through both single-factor and orthogonal experiments. It also introduces wet laser polishing as a novel method to mitigate color changes and enhance polishing effectiveness. This innovative approach demonstrates substantial improvements in performance metrics, underscoring its potential for industrial-scale production of plastic components and biomedical implants. The technique, in particular, shows promising applications in meeting the polishing requirements of 3D-printed parts.

Exploring the machining characteristics of aluminum 6061 using nanosecond pulse fiber laser machine

The present study aims to probe the influence of nanosecond laser parameters on the surface quality of aluminum material (Al 6061) using a full factorial design approach. Additionally, the study utilizes the Harris Hawks optimization (HHO) algorithm to determine the optimized laser parameters for achieving desirable surface features on straight-cut aluminum samples. Subsequently, the machined samples are analyzed through optical microscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The evaluation criteria for the present study are taper, surface roughness, and heat-affected zone (HAZ) thickness. The results revealed that average laser power significantly impacted the taper (17.01%), and scanning speed contributed significantly to the taper (26.62%). The average power and scanning speed combined showed the most substantial influence on taper (47.76%). Furthermore, the average power had the most significant effect on the heat-affected zone (77.76%) and surface roughness (SR) (72.22%). The optimal conditions determined by the HHO were a pulse frequency of 100 Hz, a scanning speed of 10 mm/s, and an average power of 40 W, resulting in heat-affected zone = 36.047, surface roughness = 5.496, and taper angle = 23.188. These findings hold significant implications for enhancing the surface characteristics of aluminum in laser machining processes, thereby benefiting industries such as aerospace, automotive, and electronics.

Experimental and simulation studies on damage characteristics, crack development patterns, and strength reduction mechanisms of sandstone under laser irradiation

In order to explore the damage characteristics and crack development laws of hard rock under laser irradiation, laser irradiation experiments on sandstone were conducted considering the interaction of three laser parameters: spot diameter, laser power, and irradiation time. Subsequently, uniaxial compression experiments were conducted on sandstone samples before and after laser irradiation. In addition, based on the maximum principal stress intensity criterion and finite element software, laser induced fracturing sandstone simulation experiments were conducted. Research has found that: Laser irradiation significantly reduces the uniaxial compressive strength of sandstone, with a maximum reduction of about 88.9%, and is also accompanied by a significant decrease in elastic modulus. The degree of sandstone damage escalates with increasing laser power and irradiation time, alongside a reduction in spot diameter. Strong correlations were observed between the strength reduction rate and crack metrics like opening, area, and depth, enabling the establishment of a high-precision regression model. Cracks originate internally within sandstone, initially extending diagonally upwards toward the specimen’s surface before propagating outward. These findings elucidate the mechanisms behind sandstone’s strength reduction and crack propagation under laser irradiation, providing some insights for the practical application of laser rock breaking technology in engineering.

Precise Laser-Modulated Anion Exchange on Ultraflexible Perovskite Films for Multicolor Patterns.

Lead halide perovskite anion exchange reactions tend to be spontaneous and rapid. To achieve precise control of anion exchange and modulate the bandgaps of perovskites to meet the demands in full-color displays, a laser-induced liquid-phase anion exchange method is developed in this paper. CsPbBr3 perovskites embedded in a polymer matrix are converted to CsPb(BrxCl1-x)3 and CsPb(BrxI1-x)3 perovskites, realizing the shift from green fluorescence to blue and red fluorescence. By changing the laser parameters, the anion exchange extent and luminescence wavelength are precisely tuned, with the maximum tuning wavelength range of 431-696 nm. Due to the focusing properties of the laser, the spatial position of anion exchange can be precisely controlled, which is significant for realizing fast and accurate patterning without masks. Based on this method, blue patterns with different light-emitting wavelengths are fabricated. RGB three-color patterns on a single perovskite composite film are successfully prepared by further replacement of halogen ions. More importantly, the polymer matrix provides ultraflexibility and good stability for the films; even if the composite films are arbitrarily folded or repeatedly bent, they can still maintain good luminous intensity. This method will show great potential in the field of flexible, full-color displays.

MoS2-based nanofluid using pulsed laser ablation in liquid for concentrating solar power plant: Thermophysical study

Concentrating solar power plants equipped with parabolic trough collectors (PTC), widely installed globally, require heat transfer enhancements in their hydraulic systems. This paper explores replacing conventional heat transfer fluids with 2D-MoS2/EG nanofluids, synthesized using the pulsed laser ablation in liquid (PLAL) method. Due to the layer-dependent physical properties of MoS2 nanosheets, tunability of PLAL in synthesizing uniform MoS2 monolayer nanosheets in EG with enhanced thermal conductivity and stability for solar PTC is essential and it is not studied thoroughly yet. Thus, this study aims to provide insights into the influence of varying laser parameters on the optical, structural, and thermal properties of MoS2-EG nanofluids and their thermal-hydrodynamical performance in solar PTC. Results show that longer ablation time, especially at higher laser energies, reduces the bandgap, thereby effectively increasing nanosheet formation. This is confirmed by phonon modes indicative of monolayer nanosheets that were outcomed from RAMAN spectroscopy. Zetasizer analysis shows that increasing the laser wavelength from 532 nm to 1064 nm reduces nanoparticle average size from 88.6 nm to 55 nm. Conversely, higher laser energy increases particle size. The optimized nanofluid improved thermal conductivity by 12.5 % at 25 °C and 13.5 % at 75 °C, maintaining a 7 % enhancement after 30 days. Analytical evaluations of solar PTC under single and counter swirl flows (SSF and CSF) show that CSF configurations with a lower twist ratio (0.4) outperform SSF, improving performance by 67 %. Furthermore, introducing optimized nanofluid by PLAL enhances performance by an 6 %. These findings underscore the potential of synthesizing MoS₂/EG nanofluids with higher thermal conductivity and stability via PLAL for enhancing CSP thermal systems.