Suitable Laser Parameters Research Articles

Geometrical modeling of ultrashort pulse laser ablation with redeposition and analysis of the influence of spot size and shape

Ultrashort-pulse lasers are an established technology for micromachining and have a great future. A major challenge remains the search for suitable laser parameters and a scanning strategy. To date, this has been achieved mainly by conducting experiments and measuring the resulting surfaces. The use of modeling methods for this purpose is not yet practical for industrial processing. In this work, the recently introduced geometric modeling method for pulsed laser ablation is applied to ultrashort laser ablation and extended to consider the power dependence of the process footprint and the pointing stability during ablation. This work highlights this modeling method to cover a wide range of process parameters in a time-saving manner and to simulate laser micromachining in real time. Furthermore, the influence of the processing height compared to the focal height on oxygen-free copper and steel 1.4034 was investigated. For both the ablation depth is decreased while simultaneously increasing the ablation width. For oxygen-free copper, the ablated volume is insensitive to changes in the processing height, which is not the case for steel 1.4034. The results also show the influence of the pulse repetition rate on the change in the shape of material removal and its influence on process stability.

Investigation on machinability of SiCp/Al composites under the synergistic effect of pulsed laser assisted and ultrasonic elliptical vibration cutting

While SiCp/Al composites are widely used in engineering applications owing to their excellent material properties, the traditional machining of SiCp/Al composites remains challenging, mainly in terms of poor surface quality and severe tool wear. In this study, a multi-energy field assisted cutting method—pulsed laser-assisted ultrasonic elliptical vibration cutting (PLA-UEVC)—for precision and high-efficiency machining of SiCp/Al composites is introduced. In this method, the intermittent impact cutting effect caused by the tool's ultrasonic frequency elliptical vibration, pulsed-laser-induced material-generated thermoelastic excitation effect, and transient temperature field synergistically work together to enhance the machinability of SiCp/Al composites. Temperature-field simulations were first utilized to simulate the temperature under suitable pulsed laser parameters. Comparative experiments with different volume fractions and particle sizes under different machining methods were conducted to evaluate the advantages of the proposed composite energy field-assisted machining method in terms of chip modulation, surface quality improvement, and tool performance improvement. The experimental results show that multi-energy field assisted cutting achieves better chip control and obtains shorter, easier-to-break chips than traditional cutting, pulsed laser-assisted cutting, and ultrasonic vibration-assisted cutting. The cutting forces of the three industrial-grade SiCp/Al6061 composites with different material properties were significantly reduced (by more than 55 %), with a surface roughness of less than 30 nm obtained for all three composites, effectively suppressing surface defects such as particle failure, thermal damage, and residual height caused by tool vibration. In addition, multi-energy field assisted cutting effectively minimized the abrasive and diffusive wear of the tool and reduced the adhesion phenomenon on the back face of the tool. These findings provide an important theoretical basis and practical machining guidance for multi-energy-field synergistic machining to improve the machinability of SiCp/Al composites.

Microchanneling and ultrasonic delivery of gold and platinum nanoparticles for selective photothermolysis of sebaceous follicles in the treatment of acne: a pilot study using porcine skin.

Several treatment options for acne vulgaris are limited by their associated adverse effects. An innovative approach involves introducing light-absorbing nanoparticles into sebaceous follicles before destroying the follicles using selective photothermolysis. We aimed to investigate efficient methods for introducing gold and platinum nanoparticles into sebaceous follicles and to identify suitable laser equipment and parameters for the effective destruction of these follicles. We used porcine skin as the experimental model. We compared the efficacies of a thulium laser, ultrasound, and manual massage and evaluated the optimal method for delivering nanoparticles in close proximity to sebaceous follicles. Subsequently, a 1064-nm-wavelength neodymium-doped yttrium aluminum garnet (Nd: YAG) laser was employed to induce selective photothermolysis. We compared different parameters to identify the optimal pulse duration and fluence of the Nd: YAG laser. The extent of penetration and destruction of sebaceous follicles was assessed using hematoxylin and eosin (H&E) staining, and a numerical evaluation was conducted. H&E staining showed that irradiation with a long-pulsed Nd: YAG laser following a combination of thulium laser and sonophoresis effectively destroyed sebaceous follicles, with destruction rates exceeding 50%. These results were valid with a long pulse duration and a high fluence of the Nd: YAG laser. This study demonstrated that sebaceous follicles can be effectively destroyed through a mixture of gold and platinum nanoparticle delivery by a combination of microchanneling and sonophoresis, followed by selective thermal damage induced by a 1064-nm long-pulsed high-fluence Nd: YAG laser.

Study on nanosecond laser-induced iron plasma reactive etching of single-crystal CVD diamond

Single-crystal diamond has great potential applications in national defense, military, and aerospace fields. However, the high hardness, chemical inertness, and anisotropy bring great challenges to machine microstructures on the diamond. Here, iron plasma, generated by infrared nanosecond laser ablation of a Fe target, was utilized to etch single-crystal diamond. The EDS, Raman, and XPS analysis revealed the formation of iron carbide within the sputtered layer surrounding the diamond microgrooves, thereby confirming that the iron plasma reacts chemically with the diamond. It was observed that employing a reactive metal, such as iron, for etching diamond microgrooves yields improved morphological characteristics and enhanced etching efficiency compared to the use of a non-reactive metal, such as copper. Moreover, the process of material removal through laser-induced iron plasma etching of diamond was elucidated. Subsequently, a systematic investigation was conducted on the impact of processing parameters on the laser-induced iron plasma etching of diamonds. Various periodic microstructures with regular edges and no chipping and cracks were successfully processed on the diamond using suitable laser parameters. This study furnishes a novel approach for the efficient fabrication of high-quality microstructures on single-crystal diamonds.

Effect of wiggler magnetic field on wakefield excitation and electron energy gain in laser wakefield acceleration

Abstract Laser wakefield acceleration is a frequently utilised research methodology for enhancing the energy levels of lighter charged particles, specifically electrons, to relativistic magnitudes. In this investigation, we utilised a linear polarised Gaussian-like laser pulse that propagated along the z-axis through cold collisionless underdense plasma in weakly nonlinear regime. An external planer magnetic wiggler field is applied along the y-axis. The influence of various critical parameters, such as amplitude and propagation constant of wiggler magnetic field, amplitude of laser electric field and laser pulse length on the wakefield and electron energy gain has been studied. A wiggler-assisted laser wakefield accelerator, the electron energy and wakefield evolution can be tuned by the wiggler magnetic field strength. The numerical findings demonstrate that by varying the strength of wiggler magnetic field and laser electric field, the amplitude of the wakefield is affected significantly. Furthermore, the equality of the order of pulse length and plasma wavelength is essential to obtain energy efficient acceleration mechanism. By employing specific parameters, a maximum energy increase of 2.26 GeV is achieved. This research will aid in the development of an energy-efficient electron acceleration technology by choosing suitable laser and plasma parameters.

Effect of Laser Power on the Recrystallization Temperature of an Additively Manufactured IN718

Over the past few decades, there has been much research on additive manufacturing in both the academic and the industrial spheres to overcome the limitations of conventional manufacturing methods, thereby enabling the production of complex designs for improved performance. To achieve this purpose, it is crucial to meticulously set suitable laser parameters within the context of microstructural characteristics, including type and fraction of defects, texture development, residual stress, and grain size, etc. In the present study, we focused on recrystallization behavior, a type of relaxation process for accumulated thermal stress during the L-PBF process, as a function of laser power applied on the L-PBF process. The laser power has significant effects on the amount of recrystallized grain, directly related to the recrystallization temperature. Within the range of laser power used in this study, a downward trend was observed in the recrystallization temperature as the laser power increased from 370 W to 390 W. This trend suggests that higher laser power leads to a faster cooling rate, influenced by the volume of melt pool as well as the amount of heat dissipation from the melt pool, resulting in higher thermal stress during the process.

SLM Additive Manufacturing of Oscillating Heat Pipe

This study employed metal additive manufacturing technology to fabricate oscillating heat pipes using SUS316L as the material and conducted related printing parameter experiments and thermal performance tests. The initial experimentation involved testing the relative density and size error of the metal additive manufacturing process. Density measurement was performed using the Archimedes method, and further X-ray CT scanning was utilized to observe the internal structure and compactness. The outcomes indicate that suitable laser parameters yield favorable results in producing oscillating heat pipes, achieving good compactness and minimal dimensional error with proper parameter adjustments. Following relevant pre-processing and post-processing on the oscillating heat pipe, leakage experiments were conducted to ensure experimental accuracy. The oscillating heat pipe had dimensions of 120 mm in length and 51 mm in width, with five turns of 2 mm × 2 mm cross-sectional channels inside. Interval design was employed to address inter-channel thermal interaction commonly encountered in flat heat pipes for comparison. Methanol was selected as the working fluid to investigate the oscillating characteristics and thermal performance under different input powers (20 W, 30 W, 40 W, 60 W, 80 W). The results indicated that the inter-channel spacing can significantly decrease the lateral thermal interaction and enhance the oscillation effect during the operation of the oscillating heat pipe, resulting in improved thermal performance. The experiments demonstrated that at 20 W, the equivalent thermal conductivity of the heat pipes with and without inter-channel spacing was 2428 and 1743 (W/mK), respectively, and at 80 W, it was 2663 and 2511 (W/mK), respectively. These results indicate that reducing thermal interaction can significantly improve the oscillation effect, leading to higher equivalent thermal conductivity at low power.

Effects of bioinspired leaf vein structure on biological properties of UV laser patterned titanium alloy

Inspired by nature, a UV laser was used to fabricate the grid and leaf vein structure on titanium alloy and polydimethylsiloxane (PDMS) coated samples, respectively. The suitable laser parameters were selected by analyzing the processing technology. The osteogenic ability of different samples and the proliferation behavior of cells on their surfaces were analyzed through cell free in vitro mineralization and cell experiments, respectively. The results show that laser patterning enhances the hydrophilicity of titanium alloy, while the -CH3 functional group in PDMS makes the sample hydrophobic. Therefore, the leaf vein structure sample appears wettability gradient by combining laser processing with PDMS material. According to the cell proliferation data, the cells maintain a good proliferation state on the four groups of samples, indicating that the samples have no cytotoxic effect. The cells are more likely to form focal adhesions and show spindle stretching on the laser patterned samples because they have more adhesion sites. For leaf vein structure, cells tend to adhere, diffuse, fuse, and proliferate in and near the leaf vein pattern. Laser patterning produces different wettability and surface morphology regions on the sample surface, and the resulting regional differentiation can be used to control the directional adhesion and growth of cells.

Laser-Induced Iridescent Steel Surfaces with Moderate Reflectance

Laser-induced coloration on metallic surfaces has emerged as a clean technology to prepare visual designs. After laser processing, the metallic surface is covered by typical periodically repeated microstructures, which interact with visible light and bring iridescent appearance to the laser markings due to the structural color effect. Although many studies have focused on this topic, the necessity of iridescent surfaces with moderate optical reflectance still needs to be addressed. In general, structural colors are shiny with high brightness. There are troubles in certain cases because shiny markings with excessive reflectance may be harmful to human eyes. In this work, we prepared iridescent an AISI444 stainless steel surface via femtosecond laser processing. By studying the influence of surface microstructures on the coloration and reflectance, suitable laser parameters for producing markings with moderate reflectance were discussed. The contribution of intrinsic colors of the chemical compositions in the surface was further analyzed.

Resonant terahertz generation from laser filaments in the presence of static electric field in a magnetized collisional plasma

A new scheme of terahertz (THz) generation from laser filaments in plasma in the presence of static electric and magnetic fields is proposed. Two femtosecond laser pulses of different frequencies ( $$\omega_{1} ,\omega_{2}$$ ) and wave numbers ( $$k_{1} ,k_{2}$$ ) are co-propagating under the action of filamentation in a magnetized collisional plasma. THz wave is generated due to the nonlinear coupling between nonlinear velocity and electron density in magnetized collisional plasma. For suitable laser and plasma parameters, the nonlinear coupling results in enhanced nonlinear current density which leads to resonant THz waves. The external D.C. electric and magnetic fields are applied perpendicular to each other and mutually perpendicular to the direction of co-propagating lasers. We have obtained the expression of a dielectric tensor with anisotropic nature, and it is found very useful in the study of THz generation. The applied magnetic field also aids to enhance the transverse components of nonlinear current. This nonlinear current is responsible to generate enhanced terahertz waves at frequency ( $$\omega_{1} - \omega_{2}$$ ). We have found that the normalized THz amplitude increases significantly with the increase in applied D.C. electric field from 10 to 30 kV/cm and magnetic field from 10 to 50kG. Our scheme with numerical analysis may open the door for efficient and cost-effective way to generate THz radiation.

Effect of Laser Parameters on Microstructure and Fracture Properties of Repaired Cracks with Micro/Nano Material Addition

Abstract Compact tension specimens with prefabricated cracks are repaired by laser with micro/nano materials added at the crack tip. Different combinations of laser parameters, i.e., laser power, laser spot diameter and heating time, were applied to investigate their effects on the microstructures and fracture properties of repaired specimens. J-integrals were calculated according to the digital image correlation (DIC) measurements, and microstructures were examined using scanning electron microscopy (SEM). When suitable laser parameters were used, homogeneous and compact equiaxed grains with no cracks, pores, and agglomeration are observed in the repaired layer, and the J-integral of repaired specimens is approximately 20% less than that of unrepaired specimen. The paper reveals relations among laser parameters, J-integrals, and microstructures, and provides a guideline for the selection of laser repair parameters.

Toward optimization of blood brain barrier opening induced by laser-activated perfluorocarbon nanodroplets.

The blood brain barrier (BBB), a component of the brain's natural defense system, is often a roadblock for the monitoring and treatment of neurological disorders. Recently, we introduced a technique to open the blood brain barrier through the use of laser-activated perfluorohexane nanodroplets (PFHnDs), a phase-change nanoagent that undergoes repeated vaporization and recondensation when excited by a pulsed laser. Laser-activated PFHnDs were shown to enable noninvasive and localized opening of the BBB, allowing extravasation of various sized agents into the brain tissue. In this current work, the laser-activated PFHnD-induced BBB opening is further explored. In particular, laser fluence and the number of laser pulses used for the PFHnD-induced BBB opening are examined and evaluated both qualitatively and quantitatively to determine the effect of these parameters on BBB opening. The results of these studies show trends between increased laser fluence and an increased BBB opening as well as between an increased number of laser pulses and an increased BBB opening, however, with limitations on the extent of the BBB opening after a certain number of pulses. Overall, the results of these studies serve as a guideline to choosing suitable laser parameters for safe and effective BBB opening.

High-sensitivity measurement of Rydberg population via two-photon excitation in atomic vapour using optical heterodyne detection technique

We demonstrate a technique based on optical heterodyne detection to measure the Rydberg population in the thermal atomic vapour. The technique used a probe beam far off-resonant to the D2 line of rubidium along with a reference beam with frequency offset by 800 MHz in the presence of a coupling laser that couples to Rydberg state via two-photon resonance. The polarisation of the probe, reference and coupling beams are suitably chosen such that only the probe beam goes through a nonlinear phase shift due to the two-photon process which is measured relative to the phase shift of the reference beam using optical heterodyne detection technique. We show that the technique has a sensitivity to measure the minimum phase shift of the order of a few $$\mu $$ rad. We have used a suitable model of two-photon excitation of a three-level atom to show that the minimum phase shift measured in our experiment corresponds to the Rydberg population of the order of $$10^{-5}$$ . The corresponding probe absorption for the given laser parameters is of the order of $$10^{-7}$$ . We demonstrate that this technique is insensitive to polarisation impurity or fluctuations in the beams. The technique is particularly useful in measuring the Rydberg population via two-photon excitation in thermal vapour where microchannel plates (MCP) could be relatively difficult to implement. It can also be used in the ultracold atomic sample with suitable laser parameters.

Effect of selective laser melting parameters on morphology, microstructure, densification and mechanical properties of supersaturated silver alloy

Silver, as a precious metal, is widely used in the consumer goods industry and high-tech fields. Selective Laser Melting (SLM), as an Additive Manufacturing (AM) technique, has the potential to make complex structural components of Ag alloy but is often limited by the high reflectivity and thermal conductivity of Ag. This study seeks to determine the optimum solution to this limitation by identifying the most suitable laser device, material and parameters for manufacturing Ag alloy through SLM. The effects of laser power, scanning speed and scanning strategy on the morphology, microstructure, density and mechanical properties of Ag alloy are described. It reveals that the density and Vickers hardness of Ag alloy are largely determined by the molten pool size, grain size, residual stress and cooling rate. Results of experiments and theoretical calculations further reveal that the heterogeneity and anisotropy formation of microstructure and defects are related to variations in the cooling rate and thermal gradient caused by the laser scanning strategy. The high scanning speed of the laser and high thermal conductivity of the Ag lead to higher cooling rates, thereby enabling SLM processed Ag alloy to have a density as high as 96.7% and hardness of up to 148.9HV.

A mixture of vortex terahertz radiation generation in inhomogeneous plasma by considering pump depletion

An attempt to extend helical terahertz radiation generation based on pump depletion is presented here. By considering an upward plasma density ramp, such a reasonable extension is examined to improve the results. It is claimed that the output terahertz energy is saturated which is attributed to laser pump divergence. The saturation effect is enhanced by considering suitable laser and plasma parameters. The adjustable slope of the density ramp is an important parameter for tuning terahertz generation efficiency, which is restricted to the up and down limit. For the resonant excitation of terahertz radiation, the ripple wave number is suitably chosen to satisfy the phase matching condition. Furthermore, as plasma frequency increases and approaches beat frequency, terahertz generation efficiency increases. Various laser and plasma parameters are employed and we report an efficiency of the order of for the current scheme.

Gaussian processes for choosing laser parameters for driven, dissipative Rydberg aggregates

To facilitate quantum simulation of open quantum systems at finite temperatures, an important ingredient is to achieve thermalization on a given time-scale. We consider a Rydberg aggregate (an arrangement of Rydberg atoms that interact via long-range interactions) embedded in a laser-driven atomic environment. For the smallest aggregate (two atoms), suitable laser parameters can be found by brute force scanning of the four tunable laser parameters. For more atoms, however, such parameter scans are too computationally costly. Here we apply Gaussian processes (GPs) to predict the thermalization performance as a function of the laser parameters for two-atom and four-atom aggregates. These predictions perform remarkably well using just 1000 simulations, demonstrating the utility of GPs in an atomic physics setting. Using this approach, we find and present effective laser parameters for generating thermalization, the robustness of these parameters to variation, as well as different thermalization dynamics.

Assessment of skin lesions produced by focused, tunable, mid-infrared chalcogenide laser radiation.

Traditionally, fractional laser treatments are performed with focused laser sources operating at a fixed wavelength. Using a tunable laser in the mid-infrared wavelength range, wavelength-dependent absorption properties on the ablation process and thermal damage formation were assessed with the goal to obtain customizable tissue ablations to provide guidance in finding optimized laser exposure parameters for clinical applications. Laser tissue experiments were carried out on full thickness ex vivo human abdominal skin using a mid-infrared tunable chromium-doped zinc selenide/sulfide chalcogenide laser. The laser has two independent channels: a continuous wave (CW) output channel which covers a spectrum ranging from 2.4 μm to 3.0 μm with up to 9.2 W output power, and a pulsed output channel which ranges from 2.35 μm to 2.95 μm. The maximum pulse energy of the pulsed channel goes up to 2.8 mJ at 100 Hz to 1,000 Hz repetition rate with wavelength-dependent pulse durations of 4-7 ns. Total ablation depth, ablation efficiency, and coagulation zone thickness were highly correlated to wavelength, pulse width, and pulse energy. Using the same total radiant exposure at 2.85 μm wavelength resulted in 10-times smaller coagulation zones and 5-times deeper ablation craters for one hundred 6 ns pulses compared to one 100 ms pulse. For a fixed pulse duration of 6 ns and a total radiant exposure of 2.25 kJ/cm2 the ablation depth increased with longer wavelengths. The tunable laser system provides a useful research tool to investigate specific laser parameters such as wavelength on lesion shape, ablation depth and thermal tissue damage. It also allows for customization of the characteristics of laser lesions and therefore facilitates the selection of suitable laser parameters for optimized fractional laser treatments. Lasers Surg. Med. 50:961-972, 2018.© 2018 Wiley Periodicals, Inc.

Characterization of recrystallized depth and dopant distribution in laser recovery of grinding damage in single-crystal silicon

A nanosecond pulsed Nd:YAG laser was irradiated on a boron-doped single-crystal silicon wafer with a diamond grinding finish to recover the grinding-induced subsurface damage. In order to visualize and measure the depth of the laser melted/recrystallized layer, small-angle beveled polishing was performed in pure water followed by KOH etching. It enabled the direct observation of the recrystallized region using a differential interference microscope and the measurement of its depth using a white light interferometer. Crystallinity analysis of the recrystallized region was carried out by using laser micro-Raman spectroscopy, and the dopant concentration profile was characterized by using radio frequency glow discharge optical emission spectrometry (rf-GD-OES). The results showed that the crystallinity and boron distribution in the recrystallized region changed after laser recovery. The dopant concentration becomes higher at the boundary of the recrystallized region and the bulk. This study demonstrates the possibility of boron concentration control by using suitable laser parameters.

Fast implementation of four-dimensional entangled state in separately coupled cavities via shortcut to adiabatic passage

Quantum information, as a comprehensive subject of quantum mechanics and information science, has a broad theoretical research value and application prospect. As a resource of quantum information, quantum entanglement has been studied thoroughly, which is not only significant to understand the features of quantum mechanics, but also of great value to the development of the method new quantum information processing. Therefore, the generation of entangled state is widely studied theoretically. In comparison to low-dimensional entangled states, multi-dimensional entangled states are not only safe but also efficient and error-tolerant for quantum computation. The adiabatic technique is one of the most widely used and proven techniques in quantum information science. The main advantages of this technique are that it is insensitive to the fluctuation of experimental parameters, and the interaction time of the system is not required to be controled accurately. However, limited by the adiabatic condition, it usually takes relatively long interaction time in scheme via adiabatic technique to achieve the target states. If the required evolution time is too long, the scheme may be useless. To overcome this problem, researchers have done a lot in the field of finding ways to shorten the long interaction time of adiabatic passage. Among these works, the technique named shortcuts to adiabatic passage is a successful work in this field and it has attracted a great deal of attention in recent years. In this paper, based on transitionless quantum driving to construct shortcuts to adiabatic passage, an efficient scheme to fast generate a four-dimensional entangled state of two-atom is proposed. The atoms are respectively trapped in the separate two-mode cavities which are connected by optical fiber. To achieve an alternative physically feasible system, the non-resonant dynamics is adopted to create a Hamiltonian which can exactly drive the system to evolve along the instantaneous eigenstates of the original Hamiltonian. As a result, if the system goes through adiabatic passage, it will evolve in the dark state, not transit to other states. Hence, using transitionless quantum driving to shortcuts to adiabatic passage, the evolutionary time in this scheme is much less than that in other schemes based on traditional adiabatic passage. The rigorous numerical simulations are conducted. The results show that with suitable pulsed laser parameters, this scheme is robust against decoherence arising from fiber decay, cavity decay and atomic spontaneous emission. Moreover, the scheme is more feasible in physics. That is, based on the proposed scheme, a high-fidelity four-dimensional entangled state of two-atom can be achieved.

Laser-assisted fixation of a nitinol stapes prosthesis.

Otosclerosis is an inner ear bone disease characterized by fixation of the stapes and consequently progressive hearing loss. One treatment option is the surgical replacement of the stapes by a prosthesis. When so called "smart materials" like nitinol are used, prosthesis fixation can be performed using a laser without manual crimping on the incus. However, specific laser-prosthesis interactions have not been described yet. The aim of the present study was to elucidate the thermo-mechanical properties of the NiTiBOND® prosthesis as a basis for handling instructions for laser-assisted prosthesis fixation. Closure of the NiTiBOND® prosthesis was induced ex vivo by either a diode laser emitting at λ = 940 nm or a CO2 laser (λ = 10,600 nm). Total energy for closure was determined. Suitable laser parameters (pulse duration, power per pulse, distance between tip of the laser fiber and prosthesis) were assessed. Specific laser-prosthesis interactions were recorded. Especially the diode laser was found to be an appropriate energy source. A total energy deposit of 60 mJ by pulses in near contact application was found to be sufficient for prosthesis closure ex vivo. Energy should be transmitted through a laser fiber equipollent to the prosthesis band diameter. Specific deformation characteristics due to the zonal prosthesis composition have to be taken into account. NiTiBOND® stapes prosthesis can be closed by very little energy when appropriate energy sources like diode lasers are used, suggesting a relatively safe application in vivo. Lasers Surg. Med. 50:153-157, 2018. © 2017 Wiley Periodicals, Inc.