Incident Angle Of Laser Beam Research Articles

Effect of laser beam incident angle on welding of Ti6Al4V with fiber lasers

Laser beam welding (LBW) is widely used for welding Ti6Al4V alloys in aerospace applications. LBW has localized high-energy fluence with low-energy input compared to other fusion welding processes, resulting in narrower heat-affected zones. On the other hand, most metals are highly reflective when the laser beam impinges perpendicular to the surface, making the process inefficient. Hence, this work proposes to employ shallow angle incidence to reduce the reflectivity during the welding of Ti6Al4V material. To explore the potential of this idea, the current study focuses on studying the effect of laser incident angle (15°-90°), power (300 W-1500 W), and feed rate (10 mm/s-25 mm/s) on autogenous weld bead geometry. For this purpose, bead-on plate (BOP) LBW is conducted on mill-annealed Ti6Al4V material of dimensions 25 mm × 25 mm × 3 mm by employing a fiber laser source with a maximum power of 3 kW and a wavelength of 1080 nm. It is observed from the results that at a normal incident angle and low laser power (< 600 W), the penetration depth is too low to generate a weld bead. Analyzing the cross-section of the weld bead, obtained from SEM, perpendicular to the weld direction reveals that the increase in laser incident angle up to an optimal angle resulted in increased bead dimensions (width and height), and beyond that, the dimensions decreased. However, the optimal incident angle changed when the laser power was changed. The major finding of this study is that at 600 W and a normal incident angle, the laser could not penetrate and generate a weld bead due to low absorptivity, while at an incident angle of 300, 450, and 600, weld beads are generated because of increased absorptivity. Similarly, the increase in weld dimensions with the increase in laser power is observed. At higher laser power, underfill and oxide formation are observed. The feed rate is less predominant than the incident angle and the power.

A novel method for fully penetrated U-rib-to-deck joints: Single-sided oscillating laser arc hybrid welding

U-rib-to-deck (RTD) joints represent one of the most critical and vulnerable welding details of orthotropic steel decks. Aiming for full penetration and high-level service performance, a novel method with single-sided oscillating laser-arc hybrid welding (OLAHW) technique was proposed for the RTD joint. The weld formation, microstructure and mechanical properties were extensively investigated. The results indicated that the porosity and lack of fusion (LoF) defects effectively suppressed with the beam oscillation during LAHW process. The OLAHW technique has good spatial accessibility with larger laser beam incidence angle of 20° Beam oscillation led to an increase in acicular ferrite in the fusion zone (FZ) while simultaneously a reduction of martensite in the heat effected zone (HAZ). This was related to the cooling time, and the thermal simulation results revealed that the OLAHW sample demonstrated comparable cooling times in both the Laser-FZ and arc-FZ. Consequently, beam oscillation can generated more homogeneous microstructures and microhardness. Although the microhardness of the OLAHW sample in the FZ was increased compared to the conventional arc welding (CAW) and LAHW sample, the highest microhardness value remained within acceptable limits (380 HV). Moreover, the ultimate tensile strength of the OLAHW weld sample increased by 7 % compared to the CAW weld sample. The application of the OLAHW technique demonstrates its feasibility for engineering applications in orthotropic steel decks manufacturing.

Effect of laser beam incidence angle on weld formation mechanism and corrosion resistance of T2 copper/304 stainless steel

Over the last 20 years, industry interest in copper has increased. Its application in the petrochemical, automotive, and nuclear power industries highlights the need for new research directions especially in the joining of copper to other metals. In this work, lap joint of 304 stainless steel and T2 copper precoated with Cu–Mn–Ni filler metal was performed by laser brazing. The aim of this study is to characterize the influence of laser beam incidence angle on the welded joint forming mode, microstructure, elements diffusion and corrosion resistance. According to the findings, the joint is classified as a welded joint when the laser beam incidence angle is 80°, and as a welded-brazed joint when it’s 90°, 70°, or 60°. The microstructure is mainly composed of Cu-rich and Fe-rich phases, Mn in the Cu-rich phase aggregation and Cr in the Fe-rich phase aggregation. In the fusion zone (FZ) the content of less than 50% of the liquid will be in the form of supersaturated droplets in the matrix of the other side. The local corrosion pair that the copper steel matrix and liquid drop produce in the FZ speeds up the dissolution of the Cu-rich phase, which effected corrosion resistance of the joint.

A Study on Length Traceability and Diffraction Efficiency of Chromium Gratings

Measurement traceability is a prerequisite for achieving accurate and reliable results as well as technical standardization. The period of Chromium (Cr) gratings fabricated by atomic lithography can be directly traced back to natural constants. Applying the Cr grating to grating interferometry can achieve nanometer measurement traceability. This research aims to analyze the diffraction efficiency characteristics of self-traceable Cr gratings to provide a theoretical basis for the fabrication and application of Cr gratings. In this regard, we establish the theoretical model of the laser beam incident angle and grating diffraction efficiency using the rigorous coupled-wave method. Then, we analyze the influence of the laser beam incident angle on grating diffraction efficiency by simulation, verify the accuracy of the theoretical model, and finally build a measurement system for grating diffraction efficiency. Through experiments, we find that the diffraction efficiency of the grating shows a rapid increase to reach a stable maximum value followed by a decrease, when a laser beam with a wavelength of 405 nm is incident on the surface of a self-traceable grating in Transverse Magnetic (TM) polarization and the incident angle changes within an effective range. The experimental results are consistent with the trend of theoretical calculation results.

Effect of laser oscillation and beam incident angle on porosity in double-sided filler welding of 2219 aluminum alloy T joint

In the current research, the double-sided laser beam oscillation filler welding (DLBOW) with beam incident angle from 20° to 40° were carried out for 2219 Al-Cu alloy T joint welding. Double-sided laser beam filler welding (DLBW) was conducted as a reference group. 3D computed tomography (CT) scanning analysis method was performed to investigate the precise three-dimensional locations of the porosity defects in the T joints. High-speed photography was conducted to evaluate the keyhole stability. The dynamic behavior of keyhole of DLBW and DLBOW was simulated by Flow-3D to study the formation process of pores. The effects of beam oscillation and beam incident angle on the macrostructure, microstructure, porosity, and mechanical property of T joints were discussed. It was found that beam oscillation and smaller beam incident angle promoted porosity suppression. The mechanical properties of T joints were improved by laser oscillation. With the beam incident angle of 20°, the porosity of T joint welded by DLBOW was lowest (0.26 %). The hoop tensile strength and T-pull tensile strength of the T joint were 403 MPa and 302 MPa, approximately 89.5 % and 71.6 %, in contrast with that of the base metal.

Dynamic Measuring Method of Laser Beam Incident Angle for Laser Doppler Vibrometer

Accurately measuring the incident angle of the laser Doppler vibrometer (LDV) laser beam is crucial for calculating the accurate dynamic response of a target. Nonetheless, conventional measuring methods may encounter limitations due to spatial constraints. To address this issue, a novel high-precision dynamic measuring method is proposed based on the measuring principle of LDV. Furthermore, a compact dynamic measuring device is constructed to facilitate this method. The proposed method involves the simulation of various tangential velocities utilizing a high precision rotating disk system. Subsequently, the laser beam incident angle is computed based on the projection relationship established between the average value of LDV measurements and the simulated velocities. To validate the feasibility of the dynamic measuring method and the correctness of the obtained incident angle, the paper compares this angle with that obtained through a conventional laser beam measuring method and device. This paper analyzes four key factors that may affect the angle measuring results theoretically and experimentally: environmental noise, laser spot position error, roll angle, and pitch angle of the rotating disk. The results indicate that the laser spot position error and the pitch angle of the rotating disk are more influential than the other two factors. Corresponding optimization measures are also proposed to improve the measuring accuracy.

A point cloud filtering method based on anisotropic error model

AbstractMany modelling applications require 3D meshes that should be generated from filtered/cleaned point clouds. This paper proposes a methodology for filtering of terrestrial laser scanner (TLS)‐derived point clouds, consisting of two main parts: an anisotropic point error model and the subsequent decimation steps for elimination of low‐quality points. The point error model can compute the positional quality of any point in the form of error ellipsoids. It is formulated as a function of the angular/mechanical stability, sensor‐to‐object distance, laser beam's incidence angle and surface reflectivity, which are the most dominant error sources. In a block of several co‐registered point clouds, some parts of the target object are sampled by multiple scans with different positional quality patterns. This situation results in redundant data. The proposed decimation steps removes this redundancy by selecting only the points with the highest positional quality. Finally, the Good, Bad, and the Better algorithm, based on the ray‐tracing concept, was developed to remove the remaining redundancy due to the Moiré effects. The resulting point cloud consists of only the points with the highest positional quality while reducing the number of points by factor 10. This novel approach resulted in final surface meshes that are accurate, contain predefined level of random errors and require almost no manual intervention.

Visible laser attenuation characteristics using various polymeric nanocomposites

The attenuation characteristic of a semiconductor laser and green laser beam power with various polymer nanocomposites including PbS, TiO2, V2O5, and CuO are investigated experimentally. Various polymeric nanocomposites with the same concentration of different nanoparticles were prepared using a solution casting technique. The distance between the sample and detector as well as the sample and laser source, and the laser beam incident angle on the surface of the sample are found to be important factors to obtain robust measurements of the attenuation of the semiconductor and green laser beam power. The nanocomposite thin film doped with CuO has more laser beam power attenuation compared to the other prepared nanocomposite thin films. Polymer nanocomposites have various applications, e.g., cut-off laser filters, optical limiting laser, and laser beam power attenuation.

Impact of a Turbulent Ocean Surface on Laser Beam Propagation.

The roughness of the ocean surface significantly impacts air-to-sea imaging, oceanographic monitoring, and optical communication. Most current and previous methods for addressing this roughness and its impact on optical propagation are either entirely statistical or theoretical, or are ‘mixed methods’ based on a combination of statistical models and parametric-based physical models. In this paper, we performed experiments in a 50-foot-wave tank on wind-generated waves, in which we varied the wind speed to measure how the surface waves affect the laser beam propagation and develop a geometrical optical model to measure and analyze the refraction angle and slope angle of the laser beam under various environmental conditions. The study results show that the laser beam deviations/distortions and laser beam footprint size are strongly related to wind speed and laser beam incidence angle.

Laser beam power attenuation characteristics for pure polyethylene oxide polymer with different thickness

This paper reports experimental investigations of the effects of various parameters on visible laser beam attenuation characteristics for organic pure polyethylene oxide (PEO) thin films. The pure PEO thin films with various thicknesses were prepared using the solution casting method. The attenuation characteristics of the prepared pure PEO were investigated using diode pumped solid state (DPSS) laser (with wavelength 532 nm), and He–Ne laser (with wavelength 632.8 nm). For both laser systems the influences of different control parameters (including linear, circular polarization states of the laser output, the separation distance between the thin films and the optical detector, and the laser beam incidence angle on thin films) on laser beam power attenuation were obtained. The DPSS laser beam output power with linear polarization has greater attenuation characteristics than other control parameters used in this work.

Expanding of Excimer Laser Photoablation’s Functionality in Ophthalmology

One of the significant weaknesses of excimer laser-based vision correction devices is the difficulty of achieving a required change in the refractive properties of the cornea to sharply focus the image on the retina with distance from the working area (ablation zone) center to the periphery due to a change in the laser beam incidence angle. The study is aimed at improving the quality of laser action on the eye cornea by introducing an optical corrective system into the existing excimer laser vision correction equipment, ensuring the coincidence of the direction of the laser beam incidence on the corneal surface with the normal.It has been shown that the greater the reflection coefficient, the lower the absorbed energy, and the shallower the laser radiation penetration and ablation depths, which reduces the laser action opportunities and quality. When using excimer laser vision correction devices, it has been proposed to change the angle of the laser beam incidence on the cornea with a distance from the working area (ablation zone) center to the periphery during the surgery by introducing an optical corrective system based on a lightweight controllable and movable mirror, which allows achieving the coincidence of the direction of the laser beam incidence on the corneal surface with the normal.The studies have shown that the coincidence of the laser beam incidence on the corneal surface at any point with the normal when using a priori data on the specifics of the patient's eye allows expanding the functional opportunities of excimer laser photoablation, i. e., expand the ablation zone by 30 % and eliminate the possibility of errors caused by the human factor. The technique proposed can be used for excimer laser vision correction according to PRK, LASIK, Femto-LASIK, and other methods. To implement this approach, a patented excimer laser vision correction unit has been proposed with a PCcontrolled optical shaping system comprising galvo motor platforms and galvo mirrors installed on them.

Thickness and Refractive Index Measurement System for Multilayered Samples

In order to simultaneously obtain the thickness and refractive index for each layer of multilayered samples, this paper proposes a novel measurement system with a simple structure by using geometric optics. The key point of the overall structure is that the binary linear equation relation between the upper and lower planes of the layer can be known by the distances between laser spots reflected from the layer. Using two optical paths with different incident angles of laser beams, the CCD sensors capture the spot signal for image processing binarization and data sampling. After the obtained laser spots' spacing is substituted into the equations, the thicknesses and refractive indexes of the multilayered samples can be calculated and measured. The proposed measurement system is characterized numerically using simulations on the commercial software program Zemax and then experimentally tested using a laboratory-built prototype. The experiment results show that the refractive indexes and the thicknesses of three-layer samples were measured with high accuracy (with maximum measurement errors of 2.4% and 2% for a refractive index n and thickness t, respectively).

Super-hard coatings deposited under conditions of the dynamic shock wave and measurement features of control parameters during production

Abstract Super-hard coatings are of increasing scientific interest as they allow synthesizing materials with unique physical and chemical properties for further application in the industry at high-speed processing or tooling. This study is aimed to investigate tetrahedral amorphous carbon (ta-C) films, as well as the dependence of the pulsation parameters on the irradiation parameters and the potential of such pulsations to be further applied in practice. The article shows that ta-C films are completely amorphous and have up to 85% of sp3 bonds. Deposited films are characterized by high compression stresses ranging within 8-10 GPa. The possibilities of reducing these stresses by thermal and pulsed laser annealing have been examined. The formation of ripples in super-hard ta-C films were studied by applying femtosecond laser pulses with a wavelength of 775 nm, an average wavelength of 387 nm, and the pulse duration of 150 fs. Obtained results demonstrated that the orientation of the pulsations on smooth surfaces is perpendicular to the vector of the electric field of the linearly polarized laser beam. Besides, the period of pulsation reduces with decreasing the laser wavelength and/or increasing the angle of laser beam incidence on the substrate.

A practical method for employing multi-spectral LiDAR intensities in points cloud classification

ABSTRACT Light Detection and Ranging (LiDAR) intensity is associated with the target surface material, which could help the points cloud classification. However, the intensity is also associated with the laser beam incident angle and the transmitting distance, which obstructs its further application in points cloud classification. Motivated by this problem, this paper proposed a practical method for employing the LiDAR intensities in points cloud classification without distance and incident angle calibration, specifically, ratio values between different spectral channels from a newly invented Hyper-spectral LiDAR (HSL) were defined and calculated for generating robust spectral features. Since the HSL different channels had the same transmitting distance and incident angle, therefore, the ratio values were independent on the laser pulse transmitting distance and laser beam incident angle. An indoor experiment was conducted for fully assessing the proposed method. The HSL had eight different spectral channels with spectral wavelength covering from 650 nm to 1000 nm. In the experiments, papers with different colours were pasted on a flat glass; the HSL scanned them at four distinctive positions with 60 cm displacement. The spectral ratio values between different channels at each position were calculated using the obtained multiple spectral profiles from the HSL. The results showed that the points cloud scanned at different incident and distance could be classified though the spectral ratio values without complex distance and incident angle calibration.

An especial configuration for an Nd:YAG end-pumped zigzag slab gain module based on crystalline polytetrafluoroethylene and a specific optical system for pump-beam delivery.

This work experimentally introduces a new single-crystal Nd:YAG end-pumped zigzag slab (EPZS) gain module based on a thin polytetrafluoroethylene (PTFE) sheet as a total internal reflection (TIR) protection layer. In this gain module, a specific optical pump-beam delivery (OPBD) system is used to improve the output beam quality (BQ) of the slab amplifier from 9.4 in a typical OPBD system to 4.7 with the total pump power of 2400 W. The average logarithmic small-signal gain (g0l) in the 0.06% Nd:YAG EPZS gain module at the laser beam incident angle of 7.1° was obtained around 0.64 for the two OPBD systems mentioned above.

Effect of laser beam incidence angle on cladding morphology in laser cladding process

The change of angle θ between laser cladding powder plane and substrate plane will lead to changes in cladding layer's geometric morphology. Therefore, we established a quantitative numerical prediction model for cladding layer geometry. In this model, we consider the variation of θ, the laser energy attenuation rate and the temperature rise of the powder particles. At the same time, the simulation results were verified by experiments. The results show that when θ is in the range of 50°~90°, the initial temperature is 298 K, the scanning speed is 3.75 mm/s, and the laser spot diameter is 4.5 mm, the Fe#1 powder cladding can achieve better forming effect on Q235. In general, with the decrease of θ, the height of the cladding layer decreases and the width of the layer increases. However, when θ is less than 50°, the quality of the formed morphology significantly deteriorated. The experimental results are in good agreement with the simulation results, which verifies the validity and reliability of the model. This work provides a theoretical reference for further understanding the relationship between the laser cladding morphology and the incident angle.

Attitude determination of Galileo satellites using high-resolution kHz SLR

A Galileo retroreflector panel was mounted on a tripod 32 km outside of the satellite laser ranging station Graz. The panel was tilted to achieve laser beam incident angles between $$0^{\circ }$$ and approx. $$18^{\circ }$$ while simultaneously doing distance measurements. At incident angles larger than approx. $$8^{\circ }$$ it was possible to identify fine structures within the data corresponding to the different columns of retroreflectors within the panel. The range differences between these columns were determined via a histogram analysis. Knowing the panel geometry it was possible to recalculate the laser beam incident angle on the panel. To compare these ground-based measurements to measurements to a specific pass of Galileo 103, matching incident angle conditions were chosen. Similar structures were found within the data set and it was possible to verify the incident angle of the laser beam. Such a method provides an excellent way to validate the attitude of Galileo satellites and is possible by analyzing the fine details of mm-accuracy kHz SLR data only.

Antibacterial properties of angle-dependent nanopatterns on polystyrene

Surface modification of polystyrene by a KrF pulse excimer UV laser under the angles of incidence of the laser beam of 0, 22.5 and 45° was proposed in this paper. The influence of the angle of incidence, laser fluence, number of pulses and a deposition of a thin gold layer on the physical and chemical properties of the surface was studied closely. Changes in the surface morphology, the formation of the periodic surface structures as well as the dependence of their dimension on the angle of incidence of the laser beam were determined by Atomic force microscopy and Scanning electron microscopy. Changes in the surface chemistry were studied by X-ray Photoelectron spectroscopy, which revealed a significant increase of oxygen concentration for all laser treated samples and also by electrokinetic analysis to further clarify the surface chemistry and charge changes occurring during the laser treatment. An optimal conditions for antibacterial surface construction was found on the basis of combination of silver nanolayer and PS treated under angle of laser beam incidence 45°. The potential application of laser-treated polystyrene foils can be found mainly in the biotechnological industry, as well as in various other fields dealing with surface modification and micro-patterning of solids.

Optimization of surgical protocol for laser iridotomy based on the numerical simulation of aqueous flow.

Primary angle-closure glaucoma (PACG) is a major cause of blindness worldwide, with a particularly high prevalence in Asian populations. Laser iridotomy (LI) has been the standard therapeutic modality for treating PACG to avoid blindness. However, the complex structure of the eyeball, the aqueous fluidity, and the limitation of detecting equipment will cause difficulty in surgery and the probability of complications. Numerical simulation was conducted to investigate aqueous humor (AH) flow under different physiological structures before and after laser surgery. When the anterior chamber depth decreases from 2.8 mm to 2.0 mm (caused by angle-closure glaucoma), the maximum velocity of natural convection is doubled, and the pressure difference between the posterior and anterior chambers increases by 20%. Therefore, a shallow anterior chamber depth is crucial for the accurate investigation of glaucoma. Pupil block sharply increases the intraocular pressure (IOP). When the gap between the lens and iris decreases from 10 μm to 0.5 μm, P between the posterior and anterior chambers is approximately 37 times higher than before, thereby damaging intraocular tissues. LI can effectively reduce the IOP caused by pupil block, but the velocity of AH after operation is 40 times the normal condition, and the increased corneal shear stress could lead to corneal damage, which can be solved by adjusting the incident angle of laser beam On the basis of the allowable angle range of surgical equipment and the effect of different incident angles on the cornea and iris, the optimum angle of laser drilling is 45°.

The Effect of Surface Waves on Airborne Lidar Bathymetry (ALB) Measurement Uncertainties

Airborne Lidar Bathymetry (ALB) provides a rapid means of data collection that provides seamless digital elevation maps across land and water. However, environmental factors such as water surface induce significant uncertainty in the ALB measurements. In this study, the effect of water surface on the ALB measurements is characterized both theoretically and empirically. Theoretical analysis includes Monte Carlo ray-tracing simulations that evaluate different environmental and hardware conditions such as wind speed, laser beam footprint diameter and off-nadir angle that are typically observed in ALB survey conditions. The empirical study includes development of an optical detector array to measure and analyze the refraction angle of the laser beam under a variety of environmental and hardware conditions. The results suggest that the refraction angle deviations ( 2 σ ) in the along-wind direction vary between 3–5° when variations in wind speed, laser beam footprint size and the laser beam incidence angle are taken into account.