Effect Of Various Laser Parameters Research Articles

Investigation of Microhole Quality of Nickel-Based Single Crystal Superalloy Processed by Ultrafast Laser

The geometric accuracy and surface quality of thin-film cooling holes have a significant impact on the cooling efficiency and fatigue life of aeroengine turbine blades. In this paper, we conducted experimental research on the processing of nickel-based single-crystal high-temperature alloy DD6 flat plates using different femtosecond laser processes. Our focus was on analyzing the effects of various laser parameters on the geometric accuracy results of microholes and the quality of the surfaces and inner walls of these holes. The results demonstrate that femtosecond laser processing has great influence on the geometrical accuracy and surface quality results of film cooling holes. Notably, the average laser power, focus position, and feed volume exert a significant influence on the geometric accuracy results of microholes. For instance, a higher laser power can damage the microhole wall, thereby leading to the formation of tiny holes and cracks. Additionally, microholes exhibit optimal roundness and taper values when using a zero defocus volume. Moreover, increasing the feed distance results in enhanced entrance and exit roundness, whereas scanning speed has a negligible impact on microhole roundness.

Influence of laser parameters on the machining performance of textured cutting tools

Over the past three decades, surface texturing has garnered significant interest as a method of controlling friction and wear in tribological systems. Surface textures play a significant role in reducing friction under dry machining conditions by lowering adhesion, decreasing the effective area of contact, and collecting wear particles. However, the effect of various laser parameters on the machining performance of textured tools is still unclear. In this research study, linear textures have been fabricated on the rake surface of uncoated carbide tools using the Nd:YAG laser by varying the laser parameters. The effect of the laser parameters, such as fluence and the average number of pulses per surface spot has been evaluated in terms of depth of textures, resolidified layer, and change in substrate hardness. The textured tools have been further used for turning the pH 13–8 Mo SS (UNS S13800) alloy under dry and wet conditions. The machining outcome results obtained with the textured tools have been compared with the plain tool. The turning experiments showed that textured tools helped in improving the machining performance by reducing the cutting forces, cutting temperature, surface roughness, and tool wear. In this research work, the textured tools fabricated with the combination of fluence = 31.4 J/cm2 and pulses per surface spot = 5 pulses/surface spot have outperformed the other textured tools fabricated with the combination of different laser parameters in terms of machining performance.

Effects of Varying Laser Parameters During Laser Stapedotomy on Intracochlear Pressures.

Sensorineural hearing loss is a known complication of stapes surgery. We previously showed that laser stapedotomy can result in intracochlear pressures that are comparable to high sound pressure levels. Optimizing laser settings to those that correspond with the lowest pressure changes may mitigate risk for postoperative hearing loss. Here we quantify the effects of various laser parameters on intracochlear pressures and test the hypothesis that intracochlear pressure changes are proportional to the laser energy delivered. Basic and translational science. Cadaveric dissection and basic science laboratory. Cadaveric human heads underwent mastoidectomies. Intracochlear pressures were measured via fiber-optic pressure probes placed in scala vestibuli and tympani. Pulses of varied stimulus power and duration from a 980-nm diode laser were applied to the stapes footplate. Sustained high-intensity pressures were observed in the cochlea during all laser applications. Observed pressure magnitudes increased monotonically with laser energy and rose linearly for lower stimulus durations and powers, but there was increased variability for laser applications of longer duration (200-300 ms) and/or higher power (8 W). Results confirm that significant pressure changes occur during laser stapedotomy, which we hypothesize may cause injury. Overall energy delivered depends predictably on duration and power, but surgeons should use caution at the highest stimulus levels and longest pulse durations due to the increasing variability in intracochlear pressure under these stimulus conditions. While the risk to hearing from increased intracochlear pressures from laser stapedotomy remains unclear, these results affirm the need to optimize laser settings to avoid unintended injury.

Numerical modeling and simulation of ultrafast laser-matter interaction with aluminum thin film

Modeling and simulation of laser-matter interaction with aluminum thin film on silicon substrate is conducted using a 1D radiation hydrodynamics code, known as HYADES. Various physical processes at the microscopic/atomic level during laser-matter interaction including laser deposition, ionization, thermal energy transport, and hydrodynamics motion are considered in the model. To validate the numerical model, single pulse laser irradiation experiments are conducted. Cross sectional profiles of the ablation sites are characterized, and ablation depths are extracted from the profiles. The numerical model is verified by comparing model predictions with experimental results. The validated model will be used in the future to study the effects of various laser parameters (e.g., laser fluence, pulse duration, laser wavelength, pulse train) on ablation efficiency and quality (e.g., ablation depth, heat affected zone).

Optimization of optical control of nitrogen vacancy centers in solid diamond

The nitrogen-vacancy (NV) centers in diamond have the advantages of stable triaxial structure, ultra-long electron spin coherence time and simple optical readout at room temperature. A nitrogen atom in the diamond crystal replaces a carbon atom and a vacancy is generated at the adjacent position, forming a point defect in the <i>C</i><sub>3<i>v</i></sub> space group structure. Its ground state and excited state are both spin triplet states. It is the key to achieving efficient preparation of optical initial state and extracting NV color center’s information in the researches of highly sensitive sensing magnetic detection, temperature detection, biological imaging, quantum computing, etc. However, there was no systematic study on relevant parameters of laser for high-concentration NV color center’s samples in previous experimental studies. Based on a high concentration diamond NV ensemble, we use pulsed optical detection magnetic resonance (ODMR) technology to systematically study the relationship among laser initial polarization time, information reading time and laser power, and the influence of laser incident polarization angle on the accuracy of sensing information. The effects of various laser parameters on the NV1 peak of ODMR on the [111] axis of the NVs of diamond are also investigated. The contrast of ODMR increases firstly with a sigmoid function and then decreases with an e-exponential function as the information reading time increases. The incident polarization angle of the laser is sinusoidal, with a period of 90°. According to the above experimental results, we finally choose the appropriate experimental parameters at 45.8 W/cm<sup>2</sup> (300 μs of polarization, 700 ns, reading time, laser incident angle is 220°) for ODMR test. Compared with previous experimental parameters (polarization time was 50 us, read the time of 3000 ns, laser incident angle was 250°), the experimental results show that the contrast of ODMR increases from 2.1% to 4.6%, and the typical magnetic sensitivity is improved from 21.6 nT/Hz<sup>1/2</sup> to 5.6 nT/Hz<sup>1/2</sup>. The optimization of the optical control of NVs in solid diamond is realized. The above results provide an effective support for the detection of high-sensitivity manipulation sensing based on high-concentration NV ensemble.

Modeling of intense terahertz wave generation with controlled field distribution

We report the results of a theoretical model and numerical investigations for an efficient intensity distribution-tunable terahertz (THz) radiation generation by two color Hermite cosh Gaussian lasers pumped in periodic density gas plasma. The effect of various laser parameters like b (decentered parameter of the cosh function), s (mode index of the Hermite function), δ (initial phase difference between two lasers), and νen (electron neutral collision frequency) on the THz field distribution, amplitude, and efficiency is investigated. The largest peak of the THz field is obtained for s=1, b=0, δ=0, π, 2π, and ω≈ωp (resonant excitation) at x=0 (forward emission in the direction of the laser propagation axis). It is found that THz radiation is highly intense for s=1, b=0, νen=0, and ω≈ωp compared to any other set of laser and plasma parameters. This study also reveals that the THz peak field and efficiency decrease monotonically with electron collision frequency. The THz field of ∼G V m−1 with an efficiency of ∼3% for the optimum laser and plasma parameters can be obtained in this scheme.

Research on 355 nm all-solid-state ultraviolet laser processing through silicon holes

In this work, the single variable method is used to investigate the effect of various laser parameters on the diameter, taper, and the quality of the through hole when silicon holes are machined with a 355 nm all-solid-state UV laser. Studies have shown that with an increase of laser fluence, the resolidification at the hole edge is alleviated, and the hole diameter increases slightly with it. The high repetition frequency aggravates the recasting on the hole walls and edges, and the hole taper is also increased due to the high repetition frequency. Excessive scanning speed causes the hole wall to be uneven and results in a large amount of melt attached to the sidewall. However, in case the scanning speed is too slow, the quality of the hole deteriorates due to severe heat accumulation. With proper negative defocus distance, the through hole with a relatively smooth sidewall and a small taper can be obtained. The results provide a technological reference for processing high quality through silicon holes by a 355 nm all-solid-state UV laser.

Fabrication of micro-features on 304 stainless steel (SS-304) using Nd:YAG laser beam micro-machining

In the present study, micro-channels and micro-dimples are fabricated with different dimensions on the surface of SS-304 alloy by pulsed Nd:YAG laser beam micro-machining. The effect of various laser parameters on the machining performance characteristics is evaluated. The effect of process parameters viz. laser scanning speed, current, laser pulse frequency and pulse duration are studied using argon gas. The width or diameter and depth of micro-features are considered as the output responses. 3D laser surface profilometer is used to study and measure the dimensions of fabricated micro-features. The results showed that the selection of micro-feature size is critical to achieve desired machining results. All the processing parameters have noticeable effect on the geometry and quality of micro-features. The dimensions (diameter, width and depth) of micro-features are decreased with higher scanning speed and increased with increase in pulse frequency, pulse duration as well as current. The appropriate combination of parameters can yield the better results for quality and size of micro-features. Lower scanning speed with higher pulse frequency with a proper set of current and pulse duration can be used in order to fabricate micro-channel, whereas higher scanning speed and lower pulse frequency can be used to obtain micro-dimples.

Facile fabrication of flexible all solid-state micro-supercapacitor by direct laser writing of porous carbon in polyimide

We demonstrate the fabrication of flexible micro-supercapacitors based on laser carbonization of polyimide sheets. Localized pulsed laser irradiation rapidly converts the pristine polyimide surface into an electrically conductive porous carbon structure in ambient conditions. Thus, the polyimide sheet acts as both a precursor for the carbonization and a flexible substrate. Effects of various laser parameters are examined to enhance electrical properties and morphology of the carbonized structures. The interdigitated electrode patterns are produced directly on the polyimide sheets by programmed laser scanning. A solid-state polyvinyl alcohol–phosphoric acid gel electrolyte is introduced into the active electrode area to realize a flexible all solid-state microcapacitor assembly. Cyclic voltammetry measurements exhibit the expected electrical double layer behavior. The specific capacitance of the supercapacitors reaches ∼800μF/cm2 at a voltage scan rate of 10mV/s with good capacitance retention under mechanical bending. The proposed laser-based approach enables facile fabrication of flexible micro-supercapacitors without tedious photolithographic patterning of porous carbon and metal current collectors.

Microstructural and hardness investigation of tool steel D2 processed by laser surface melting and alloying

Several techniques can be used to improve surface properties of metals. These can involve changes on the surface chemical composition such as alloying or on the surface microstructure, such as hardening. In the present work, melting of the surface by a 9 kW CO2 CW laser of wavelength 10.6 μm was used to alter surface features of D2 tool steel. Carbon powder and nitrogen gas were used as sources of alloying elements during laser processing. The effect of various laser parameters (power and speed) on the microstructure and hardness of D2 tool steel was investigated. Laser powers from 1 to 8 kW and laser speeds from 5 to 15 mm/s were employed. It was found that as the laser power increases, the hardness of the melted zone decreases while that of the heat-affected zone increases. On the other hand, the depth of both of melted and heat-affected zones increases with power.

Laser Surface Annealing of Plasma Sprayed Coatings

Laser surface annealing provides a rapid and efficient means for surface alloying and modification of ceramic materials. In this study, Alumina-13% Titania coatings were sprayed with a water-stabilized plasma spray gun. The coated surface was treated by Excimer laser having a wavelength of 248 nm and pulse duration of 24 ns. The surface structure of the treated coating was examined by field emission scanning electron microscope and X-ray diffraction (XRD). A detailed analysis of the effects of various laser parameters including laser energy density (fluence), pulse repetition rate (PRR), and number of pulses on the morphology and the microstructure of the coatings are presented.

Investigation of Femtosecond Laser Irradiation on Fused Silica Etching Selectivity

ABSTRACTFemtosecond laser irradiation has various noticeable effects on fused silica. It can locally increase the index of refraction or modify the material chemical selectivity. Regions that have been exposed to the laser are etched several times faster than unexposed regions. Various observations reported in the literature seem to show that these effects are possibly related to a combination of structural changes and the presence of internal stress. However, a detailed analysis of the contribution of both effects is still lacking.In this paper, we present systematic SEM-based investigations performed on fused silica (a-SiO2). Line-patterns were first scanned on the substrate using a femtosecond laser and then etched in a low-concentration HF solution. The effects of various laser parameters like power and scanning speed are analyzed and we show further evidence of an interface between two different etching regimes.

Time-resolved parametric studies of laser ablation using inductively coupled plasma atomic emission spectroscopy

The quantity of ablated mass and its composition strongly depend on the number of laser pulses and laser fluence at the sample target surface. For chemical analysis, thin-film deposition, cutting, and other laser-ablation applications, the quantity of mass removed vs. number of laser pulses is important. In addition, the composition of the vapor can be critical, for example, in providing accurate chemical analysis or well-defined thin film structures. In this work, mass ablation rate and ablated mass composition were studied by monitoring the time dependence of emission intensity using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP) during repetitive laser ablation at a single location on the sample target. Spectral emission intensity in the ICP is directly related to the quantity of mass ablated by the laser. The ratio of spectral emission lines in the ICP gives an indication of the relative composition of ablated constituents. In this work, a brass sample was ablated using several lasers with various properties. Emission intensities of Cu and Zn ionic lines, after the occurrence of an initial signal spike, increase with increasing number of laser pulses at high fluence, whereas at low fluence no significant changes were observed in the mass ablation rate. The zinc-to-copper ratio was used to monitor fractionation processes during repetitive laser ablation. The ratio increased with increasing ablation time at low fluence. In contrast, the ratio was almost constant, and close to the accurate level at high laser fluences. The effect of various laser parameters on the mass ablation rate and mass composition are discussed in this paper.

Two-dimensional model for material damage due to melting and vaporization during laser irradiation

A two-dimensional model is developed for material damage caused by melting and vaporization during pulsed laser irradiation. The problem is formulated by using the energy conservation equation (the Stefan condition) at various points on the solid-liquid and liquid-vapor interfaces. The effect of curvature of the solid-liquid and liquid-vapor interfaces are taken into account and the problem is solved numerically by using the Runge–Kutta method. For determining the maximum damage that can occur during laser irradiation, the laser energy is considered to be utilized only to melt and vaporize the material. The effect of various laser parameters, such as the laser power, laser beam diameter, pulse-on time, and the number of pulses per second on the depth and the radius of the crater is presented. Also, the tapering angle of the crater and the formation of recast layer in the crater during laser irradiation are examined in this study. Finally, a linear relationship between the maximum crater depth and the ‘‘gross’’ laser intensity is derived phenomenologically and verified by using the numerical results of this study.

Laser Cladding of Thermal Barrier Coatings

The feasibility of laser cladding zirconia and alumina thermal barrier coatings on Udimet 700 alloy and AISI 4140 steel substrates was investigated; the objective was to extend the high temperature performance of thermal barrier coatings. Two continuous wave CO2 gas lasers with power levels of 1.2 and 5 kW were employed for cladding. Laser power, powder flowrate, scanning spot size, and travel speed were the major parameters varied during cladding. Zirconia claddings obtained were thin (5–15 μm), dense, hard (800–1700 HV0.2), and crack free, possessing unusually fine microstructures, glassy surfaces, excellent adhesion, and good surface integrity. It was possible to produce thicker claddings, but these tended to crack, delaminate, and chip off from the substrate. The power density was the key process variable that determined the transition from a thicker, cracked coating to a thin, crack free one. The results indicate that a promising approach to generating thicker flawless claddings would be one based upon an improved understanding of the role of power density on the mechanism of melt pool formation. Data are presented on the effects of various laser parameters and coating powder variables on clad thickness and quality.