Modulation Of Laser Beam Research Articles

New insight into microstructure and mechanical properties of heterostructures 7075 Al joint prepared via single mode laser welding

The application of lightweight and high-strength Al alloys are crucial to reduce energy consumption and emissions in today's world. The lightweight and high strength 7 series aluminum alloy is widely used in aerospace, but its poor welding performance has been a bottleneck restricting the further lightweight of structural parts. In this work, a lightweight and high-strength Al joint with a tensile strength of ∼400 MPa was successfully prepared by single mode laser beam welding using non-weldable 7075 aluminum alloy as the experimental mode. The superfine laser beam reduces the volume of molten pool and increases the solidification rate of molten pool, which significantly inhibits the growth behavior of each microstructure, thus refining the microstructure. The geometrically necessary dislocations (GND) density of each microstructure of 7075 joint after tensile test was: 1.32 × 1014 m−1 for EZ, 1.21 × 1014 m−1 for CLZ, HAZ is 1.17 × 1014 m−1 for HAZ. The synergistic effect of heterogeneous microstructure and work hardening enhanced the tensile strength of 7075 joint. Furthermore, TEM, FIB and EBSD were used to characterize the fracture behavior of the 7075 joint in detail. TEM images showed that the discordant interface between α-Al grain boundary and SiO2 particle was the potential source of crack initiation. The microstructure refinement design and technical selection strategy of the work provide a new insight for laser welding of lightweight and high strength 2xxx/7xxx aluminum alloy.

Self-focusing, self-trapping and self-phase modulation of elliptical q-Gaussian laser beams in collisionless plasma

Self-focusing, self-trapping and self-phase modulation of elliptical q-Gaussian laser beams in collisionless plasma

Theoretical studies of high-power laser beam smoothing via stimulated brillouin scattering in plasma

To achieve uniform irradiation, the focal spot from a high-power laser system must be homogeneous; thus, laser beam smoothing is required. In this study, we theoretically demonstrated a novel spatial smoothing method based on stimulated Brillouin scattering (SBS) in a plasma. As SBS is sensitive to pump intensity, the area of higher intensity in the laser beam has a higher reflectivity, leading to a more homogeneous passed beam. From the theoretical simulation, the laser beam modulation significantly decreased in SBS, while the fluence contrast decreased from 15.9% to 9.7%.

Application of adjustable ring mode laser in remote laser welding of additive manufactured AlSi10Mg alloy

Additive manufacturing (AM) is an innovative manufacturing technology that offers the ability to build parts with both geometric and material complexities. However, limitations, including low build volume capability and production rate, yield its rapid application in high volume production. This paper presents the potential of remote laser welding (RLW) as a post-AM joining approach to scale up the AM components. The AM AlSi10Mg alloy was fabricated by direct metal laser sintering and subsequently joined by RLW without filler wire or shielding gas. A novel adjustable ring mode (ARM) laser beam was employed during the RLW process where the ring beam is designed to stabilize the keyhole by providing the preheating and postheating while the core beam guarantees a sufficient weld penetration. The impact of the ARM laser on weld porosity was evaluated in both fillet lap and bead-on-plate welding configurations, accompanied by the variation of core/ring beam power ratios. Crack-free welds with promising weld appearance were obtained among all welding trials, indicating that the ARM-RLW process can be employed for the robust connection of AM AlSi10Mg alloys. Optimizing the power ratio can substantially reduce the weld porosity area ratio from 24.3% to 13.5% in the fillet lap configuration and from 24.2% to 14.4% in the bead-on-plate configuration. Analysis of variance tests statistically confirmed the significant impact of the power ratio on the porosity area ratio. Future work has been suggested for the process maturation of RLW as a post-AM joining approach in industrial application.

An efficient ultrasound-assisted CH3COONa catalyzed synthesis of thiazolidinone molecule: Theoretical and nonlinear optical evaluations of thiazolidinone-Schiff base derivative

Chemical synthesis, structural analysis, theoretical calculations and optical properties exploration of (E)-2-((E)-(4-nitrobenzylidene)hydrazono)-3-phenyl-4-thiazolidinone 7 (C16H12N4O3S) are introduced. The synthesis method involves three steps. The applying of 1H and 13C NMR, infrared radiation (IR), mass and UV–visible spectroscopies and melting point (m.p) confirmed the expected compound structure. Optimization of the compound geometrical structure is carried out via the theoretical calculation and evaluation of its nonlinear optical (NLO) properties. The NLO properties of the synthesized 4-thiazolidinone derivative 7 are studied under the irradiation with visible and single transverse mode laser beam, through the determination of the nonlinear refractive index (NRI) via the diffraction ring patterns (DRPs) and the Z-scan together with optical limiting. Using two visible laser beams, the all-optical switching (AOS) in 4-thiazolidinone derivative 7 is studied too.

Position coding as a means of increasing the range of optical communications links

Subject of study. We present research on the range of atmospheric optical communications links as a function of atmospheric conditions, the types of laser beam modulation used, and the type of interference-resistant coding used. Aim. We develop an approach for increasing the range of free-space optical communications links by improving resistance to atmospheric turbulence. Methods. We show that the modulation technique and channel coding must be compatible if optimum results are to be achieved. Pulse position modulation and interference-resistant position coding are one example of such a compatible combination; a holographic code in which a sequence of pulses representing a 1D linear hologram of a single pulse replaces a single pulse in the desired position is one example of an interference-resistant code. In this case, position modulation is still being used, but in the form of multiple pulse position modulation. A holographic code takes advantage of the fact that holograms are divisible, and a fragment of the hologram can be used for recovery of transmitted data (as well as data hidden by noise). The recovery capacity of the holographic code depends on the hologram length—the number of slots per symbol interval. Main results. We show that holographic coding provides higher interference resistance and a lower probability of detector error and provides the same benefit as an increase in transmitter power. Practical significance. The benefit from holographic coding may be used to either increase the communications range or increase the communications channel reliability. Position coding has the advantages that the redundant information required for interference-resistant encoding is created within the symbol interval, does not affect the symbol repetition frequency, and has no effect on the data transmission rate.

Mode division multiplexing free space optics system with 3D hybrid modulation under dust and fog

Mode division multiplexing (MDM) is an emerging information transmission technique in which multiple data signals can be transmitted simultaneously on different modes of a single wavelength laser beam over a free-space channel. MDM is a potential technique for the realization of high-speed spectral efficient communication links for future generations of wireless networks. We present a novel MDM-based free-space optics (FSO) system. The system integrates a 3D hybrid modulation scheme produced by combining carrier suppressed-non-return-to-zero (CSNRZ), differential quadrature phase-shift keying (DQPSK), and polarization shift keying (PolSK) modulation schemes for beyond 100 Gbps applications. Three unrelated 40 Gbps data signals are modulated and transmitted on one optical carrier utilizing three distinct signal properties: amplitude (CSNRZ), phase (DQPSK), and polarization state (PolSK). The proposed 3D modulation scheme offers a high-capacity system, where each channel transmits 4 Gbps as compared to 1 Gbps in the case of OOK modulation. MDM using distinct Hermite Gaussian modes: (HG00 and HG01) of a laser beam is incorporated to boost the spectral efficiency and information rates of the FSO link. The proposed 120 Gbps single-channel MDM-FSO link performance is examined under the impact of different levels of dust and fog environmental conditions using quality factors and received eye diagrams as the performance metrics. This system achieved optimal performances up to 1250 m (very light dust), 540 m (light dust), 170 m (moderate dust), 750 m (low fog), and 425 m (medium fog). In the worst-case scenario, the system manages to work up to a 67 m range in dense dust with a maximum attenuation of 297.38 dB/km and a 200 m distance in heavy fog with only 90 dB/km attenuation which is less than 1/3rd of the attenuation measured for dense dust event. In addition, our results and the case studies confirm that dust introduces greater signal attenuation than fog. Therefore, an encounter with a dust environment should be considered as the bottleneck issue for FSO links. The creative contribution of this paper is to put forward a bandwidth-efficient MDM-FSO-enabled B5G system that could be deployed in harsh and challenging locations at reduced visibility. This is expected to be further technically sustainable owing to the use of advanced 3D hybrid optical orthogonal modulation and therefore find use in implementing 5G and 6G cellular and data networks.

Microstructure and Mechanical Properties of Laser Narrow-Gap Multi-Pass Weld 20 mm-Thick Ti-6Al-4V Alloy with Different Filling Layers

In the narrow-gap multi-layer welding of thick Ti-6Al-4V titanium alloy sheets, reducing the number of filling layers can effectively improve the welding efficiency and reduce the possibility of interlayer defects. In order to explore the changes in the microstructure and properties of the weld after reducing the number of filling layers, Ti-6Al-4V titanium alloy sheets with a thickness of 20 mm were successfully welded using the oscillating laser beam mode by laser narrow-gap multi-pass wire filler welding in eight, six, four, and three layers, and all of the formations were good. To reduce the number of filling layers and increase the welding line energy from 0.4 kJ/mm to 1.2 kJ/mm, the melting depth and width of the single layer were changed from 4.3 mm to 10.6 mm, and 5.7 mm to 10.3 mm. The average grain size of the needle-shaped martensite increased from 1.83 μm to 2.38 μm, while the tensile strength of the filled weld area decreased from 1301.8 MPa to 1169.8 MPa, which was higher than that of the base metal of 902.1 MPa. Since there are more columnar crystals in the center of the weld at low heat input, the impact energy was 20.53 J (60.6% of the base metal) at room temperature and 15.76 J (65.9% of the base metal) at −50 ∘C. Considering the weld formation, microstructure and mechanical property, welding four layers of fillers obtained with moderate line energy (0.8 kJ/mm) was more suitable.

High power laser powder bed fusion of AlSi10Mg alloy: Effect of laser beam mode

High power laser powder bed fusion (HP-LPBF) is a burgeoning additive manufacturing technology for the high-efficiency and high-accuracy build of metallic parts. However, studies about the effect of laser beam mode on build quality is still insufficient. In this paper, both a 2 kW multi-mode fiber laser and a 2 kW Gaussian mode fiber laser are used for the HP-LPBF of AlSi10Mg alloy. Firstly, the relative density (RD) of the HP-LPBF samples has been studied for parameter optimization. The RD of the samples built with the multi-mode laser beam (hereafter called as Multi-mode sample) first increases and then remains stable with the increase of laser energy density Ev. When Ev is no less than 50 J/mm3, the RD of the Multi-mode sample is higher than 99.5%. In contrast, the RD of the samples built with the Gaussian mode laser beam (hereafter called as Gaussian sample) first increases and then decreases with the increase of Ev, and the highest RD is just 95.87 ± 0.2% at the Ev of 50 J/mm3. Based on this, the Multi-mode sample and Gaussian sample built with the same parameters (Ev=50 J/mm3) are chosen as the typical contrast samples for further studies of surface quality, microstructure and tensile property. The results show that the typical Multi-mode sample presents a flatter surface and a lower surface roughness compared with the Gaussian sample. The phase composition of both the two kinds of samples consists of α-Al matrix and eutectic Si. However, the solidification microstructure varies with laser beam mode. The Multi-mode sample presents a columnar solidification microstructure with a strong< 100 > texture along the build direction. In contrast, the solidification microstructure of the Gaussian sample is a mixture of equiaxed grains and short columnar grains. The crystallographic orientations of the two kinds of grains are multifarious, leading to a much weaker texture. The tensile strengths and elongation of the Multi-mode sample are significantly better than those of the Gaussian sample. The effect mechanisms of the laser beam mode on relative density, surface quality, microstructure and tensile property have also been revealed.

Particle deceleration for collective QED signatures

Frequency upshifts have been proposed as a first experimental signature of collective effects in quantum electrodynamic cascade generated electron–positron pair plasmas. Since the high effective masses of generated pairs will reduce any frequency change, stopped pairs at a minimal Lorentz factor in the lab frame were thought to be the dominant contribution to the laser upshift. However, we demonstrate that only considering stopped particles unduly neglects the contributions of particles re-accelerated in the laser propagation direction. Re-accelerated particles should, on a per particle basis, affect the laser more strongly and over a much longer timescale. To maximize particle contributions to the laser upshift, we consider a Laguerre–Gaussian (LG) mode laser beam to better reflect generated pairs. The LG mode does not have an advantage in particle deceleration and re-acceleration when compared against a Gaussian beam, but the LG mode can maintain particle contributions for a longer duration, allowing for more pair density accumulation. Deceleration with a structured beam to keep pairs within the laser should create a larger upshift, thereby lowering the demands on the driving laser.

Spatial self-phase modulation with tunable dynamic process and its applications in all-optical nonlinear photonic devices

In the spatial self-phase modulation (SSPM) experiments, the gravity-promoted thermal convection effect will lead to the distortion of self-diffraction ring in the evolution process. Generally, this distorted diffraction ring affects the SSPM applications in nonlinear photonic devices. In this work, for the first time to our knowledge, we use a cylindrical lens (CL) focusing laser beam to study the SSPM effect of black phosphorus (BP) suspensions. By adjusting the orientation angle θ between the CL's axis and the vertical direction, so as to change the effective area of thermal convection, we experimentally demonstrate the SSPM behavior with tunable dynamic process. As the angle θ increases from 0° to 90°, that is, the effective area of thermal convection becomes larger, we find that the formation times of complete symmetric diffraction ring and distorted diffraction ring become shorter and longer, respectively. In addition, based on the spatial cross-phase modulation (SXPM) of the CL focusing laser beam, we realize the all-optical switch and all-optical information converter that can relatively control the response time.

DFT calculation and nonlinear optical properties of (E)-(2)-((8-hydroxyquinolin-5yl)diazenyl)-5-sulfamoylpheneyl)mercury(II) chloride

The molecular structure of mercurated azo compound (A1), (E)-(2-((8-hydroxyquinolin-5-yl)diazenyl)-5-sulfamoylphenyl)mercury(II) chloride, is investigated theoretically by the DFT with the GGA approximation, PEB level and DNP as basis set. The nonlinear optical (NLO) properties of the synthesized azo compound are investigated using a continuous wave (cw), low power, with TEM00 mode laser beam using the methods diffraction ring patterns (DRPs) and Z-scan. The nonlinear refraction index (NRI) is calculated based on both methods where as high as 5.28 × 10−7 cm2/W of the NRI is determined via the DRPs. The optical limiting (OLg) property of the A1 compound is examined with limiting threshold of 10 mW is determined. The experimentally determined DRPs are simulated via Fresnel-Kirchhoff integral with good accord of experimental and theoretical results.

Preliminary Study on Detecting the Internal Voltage Values of Integrated Circuits Based on Electro-Optical Frequency Mapping

Electro-optical frequency mapping (EOFM) technology can detect node signals from the backside of integrated circuits (ICs). In the past, the detected signal only qualitatively represented the electrical activity strength inside the device. In this paper, the electro-optical signal generation mechanism of the device is systematically studied, and a concise physical model of laser beam modulation based on the optical transmission matrix is proposed. Firstly, the influence of the bandwidth of the laser and each structure covered by the laser spot on the electro-optical signal of the device is well described by the model. Secondly, the model quantifies the electro-optical signal strength, and shows it is positively correlated with the laser wavelength and the reverse bias voltage. Finally, the model is used to quantitatively calculate the accurate voltage level of the internal node inside the device using the detected signal, and the calculation results match well with the experimental results. The model provides theoretical guidance for the efficient and accurate extraction of internal voltage values of devices by EOFM technology.

Influence of Laser Beam Wobbling Parameters on Microstructure and Properties of 316L Stainless Steel Multi Passed Repaired Parts.

The results of experimental studies of repair of the supporting structure components made of 316L steel multi-pass laser cladding with filler wire are presented. The influence of the wobbling mode parameters, welding speed, and laser power on the formation of the deposited metal during multi-pass laser cladding with filler wire of 316L steel samples into a narrow slot groove, 6 mm deep and 3 mm wide, are shown. Non-destructive testing, metallographic studies, and mechanical tests of the deposited metal before and after heat treatment (2 h at 450 °C) were carried out. Based on the results of experimental studies, the optimal modes of laser beam wobbling were selected (amplitude—1.3 mm, frequency—100 Hz) at which the formation of a bead of optimal dimensions (height—1672 μm, width—3939 μm, depth of penetration into the substrate—776 μm) was ensured. A laser cladding technology with ESAB OK Autrode 316L filler wire has been developed, which has successfully passed the certification for conformity with the ISO 15614-11 standard. Studies of the chemical elements’ distribution before and after heat treatment showed that, after heat treatment along the grain boundaries, particles with a significantly higher Mo content (5.50%) were found in the sample, presumably precipitated phases. Microstructure studies and microhardness measurements showed that the upper part metal of the third pass, which has a lower microhardness (75% of base metal), higher ferrite content, and differently oriented dendritic austenite, significantly differs from the rest of the cladded metal.

All-Fiber Cascaded Combiners for High-Power Adjustable-Ring Mode Laser Beam with a Flattop Central Beam

All-Fiber Cascaded Combiners for High-Power Adjustable-Ring Mode Laser Beam with a Flattop Central Beam

Two Laser Beam Modulation of Microstructure and Residual Stress Field in Cold Sprayed Al Alloy for Recovering Fatigue Performance

Two Laser Beam Modulation of Microstructure and Residual Stress Field in Cold Sprayed Al Alloy for Recovering Fatigue Performance

Measurement of thermal diffusivity of gold nanofluid according to particle size and temperature

The thermal diffusivity of a gold nanofluid containing 20, 40, or 80 nm particles prepared by dispersing gold nanoparticles in ethylene glycol was measured from room temperature to 80°C using the thermal lens effect in dual laser beam mode consisting of an excitation laser (532 nm) and a probe laser (633 nm). Three samples with three different nanoparticle sizes were prepared at the same concentration (3 × 10-5 wt.%). The thermal diffusivity was 1.020 × 10-7 m2/s (20 nm), 1.379 × 10-7 m2/s (40 nm), and 2.126 × 10-7 m2/s (80 nm) at RT, and 1.211 × 10-7 m2/s (20 nm), 1.784 × 10-7 m2/s (40 nm), and 2.758 × 10-7 m2/s (80 nm) at 80°C. Overall, the thermal diffusivity of a gold nanofluid was proportional to the nanoparticle size and increased with increasing temperature.

Keyhole dynamic status and spatter behavior during welding of stainless steel with adjustable-ring mode laser beam

A novel adjustable-ring mode laser (ARM) welding of SUS304L stainless steel sheet was investigated in this work. The ARM laser consists of two parts: ring laser beam as outer part; circular laser beam as center part. A Phantom high-speed camera with image processing algorithm was used to monitor the keyhole dynamic behavior. The spatter ejection, molten pool, and keyhole status were observed from the top view position. The characteristics of spatters were monitored from the side position of the camera. Experimental results showed that the pure circular laser beam (regular Gaussian beam) generated a periodic opening and collapsing keyhole with plenty of spatters in the welding process. However, the pure ring laser beam generated a continuously opening keyhole-inlet in the welding process. Because of the ring laser on welding, the dual-mode ring/circular laser (ARM laser) maintained a relatively opening keyhole with a smaller number of spatters comparing to pure circular laser welding. This work provided a full understanding of the process mechanism regarding the welding with shaped laser beam. The adjustable-ring mode laser is expected to be applied in a high-quality industrial manufacturing process.

Electron Bernstein wave aided heating of collisional nanocluster plasma by nonlinear interactions of two super-Gaussian laser beams

In this present theoretical study, we investigate electron Bernstein wave (EBW) aided collisional nanocluster plasma heating by nonlinear interaction of two super-Gaussian laser beams. The interactions of laser beams electric field profiles with electronic clouds of nanoclusters cause the beat wave. The nonlinear ponderomotive force is generated through the beat wave. There may be good potential to excite the EBW aiding cluster plasma to lead electron heating via cyclotron damping of the Bernstein wave. An analytical scheme is proposed for the anomalous heating and evolution of electron temperature by using this mechanism. Graphical discussions were promised to achieve extreme heating rate via the spatial shape of super-Gaussian laser beams and the resonance condition of beat wave to surface plasmon frequency. The heating is controlled by tuning the laser beam width, mode index, collisional frequency, clustered radius, and density.

Self focusing and axial phase modulation of laser beams carrying orbital angular momentum in collisionless plasmas

Self focusing and axial phase modulation of laser beams carrying orbital angular momentum in collisionless plasmas