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Micromachines
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Optical and Laser Material Processing
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Optical and Laser Material Processing

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D：Materials and Processing".

Deadline for manuscript submissions: 31 January 2025 | Viewed by 6688

Special Issue Editors

Prof. Dr. Yuankun Lin

E-Mail Website
Guest Editor
Department of Physics, University of North Texas, Denton, TX 76203, USA
Interests: nanophotonics; laser holographic fabrication; 2D materials
Dr. Yuzhe Xiao

E-Mail Website
Guest Editor
Department of Physics, University of North Texas, Denton, TX 76203, USA
Interests: nanophotonics; ultra-fast laser; quantum plasmonics

Special Issue Information

Dear Colleagues,

Products and services based on nanotechnology are becoming increasingly important to our economy, and so is the optical and laser processing and manufacturing technology that produces them. Two- and three-dimensional nanofabrication can be addressed using both top-down and bottom-up approaches. Bottom-up approaches have enabled large-scale additive and selective laser manufacturing. Top-down methods (including EUV lithography) have resulted in computer chip manufacturing. Combining top-down and bottom-up approaches can facilitate the integration of different dimensions and scales in optical and laser material processing, including the direct laser writing of 2D-layered materials in pattern. Thus, this Special Issue seeks to showcase research papers and reviews on new developments in optical and laser material processing for micro- and nano-scale manufacturing.

We look forward to receiving your submissions!

Prof. Dr. Yuankun Lin
Dr. Yuzhe Xiao
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • material-based micro/nano structures and devices
  • optical and laser material processing
  • optical- and laser-based nano/micro-fabrication
  • 2D and bulk material processing

Published Papers (9 papers)

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Research

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19 pages, 12227 KiB  
Article
Research on Polarization Modulation of Electro-Optical Crystals for 3D Imaging Reconstruction
by Houpeng Sun, Yingchun Li, Huichao Guo, Chenglong Luan, Laixian Zhang, Haijing Zheng and Youchen Fan
Micromachines 2024, 15(8), 1023; https://doi.org/10.3390/mi15081023 (registering DOI) - 11 Aug 2024
Abstract
A method for enhancing the resolution of 3D imaging reconstruction by employing the polarization modulation of electro-optical crystals is proposed. This technique utilizes two polarizers oriented perpendicular to each other along with an electro-optical modulation crystal to achieve high repetition frequency and narrow [...] Read more.
A method for enhancing the resolution of 3D imaging reconstruction by employing the polarization modulation of electro-optical crystals is proposed. This technique utilizes two polarizers oriented perpendicular to each other along with an electro-optical modulation crystal to achieve high repetition frequency and narrow pulse width gating. By varying the modulation time series of the electro-optical crystal, three-dimensional gray images of the laser at different distances are acquired, and the three-dimensional information of the target is reconstructed using the range energy recovery algorithm. This 3D imaging system can be implemented with large area detectors, independent of the an Intensified Charge-Coupled Device (ICCD) manufacturing process, resulting in improved lateral resolution. Experimental results demonstrate that when imaging a target at the distance of 20 m, the lateral resolution within the region of interest is 2560 × 2160, with a root mean square error of 3.2 cm. Full article
(This article belongs to the Special Issue Optical and Laser Material Processing)
►▼ Show Figures

Figure 1

Figure 1
<p>Schematic diagram of the modulation process of a crystal by EMCCD imaging.</p> Full article ">Figure 2
<p>Schematic diagram of 3D imaging reconstruction based on polarization modulation gating of electro-optical crystal.</p> Full article ">Figure 3
<p>Signal timing diagram.</p> Full article ">Figure 4
<p>Schematic diagram of crystal polarization-modulated gated 3D imaging: (<b>a</b>) 3D imaging process; (<b>b</b>) 3D imaging restoration.</p> Full article ">Figure 5
<p>Three-dimensional imaging distance–energy diagram: (<b>a</b>) laser pulse and crystal shutter; (<b>b</b>) the relationship between the echo energy and the target distance.</p> Full article ">Figure 6
<p>Schematic diagram of the energy of two echo signals.</p> Full article ">Figure 7
<p>Distance grayscale curve of a trapezoid.</p> Full article ">Figure 8
<p>The propagation of light in an electro-optical crystal.</p> Full article ">Figure 9
<p>SRefractive index ellipsoid.</p> Full article ">Figure 10
<p>Polarization modulation of electro-optical crystal light intensity distribution. (<b>a</b>) the light intensity distribution of the electro-optical crystal in the “off” state; (<b>b</b>) the light intensity distribution of the electro-optical crystal in the “on” state.</p> Full article ">Figure 11
<p>Schematic diagram of crystal polarization modulation.</p> Full article ">Figure 12
<p>The prototype of the 3D imaging system is based on electro-optical crystal polarization modulation.</p> Full article ">Figure 13
<p>Three-dimensional imaging target. (<b>a</b>) semi-ellipsoidal object; (<b>b</b>) satellite object; (<b>c</b>) space station object.</p> Full article ">Figure 14
<p>Waveform diagram of the laser pulse and electro-optic-modulated shutter signal. (<b>a</b>) Laser pulse waveform; (<b>b</b>) The electro-optical crystal modulates the shutter waveform.</p> Full article ">Figure 15
<p>The timing relationship between the laser pulse and electro-optical-modulated shutter signal. (<b>a</b>) The laser pulse signal is tangent to the electro-optical crystal-modulated shutter; (<b>b</b>) The laser pulse signal enters the electro-optical-modulated shutter completely.</p> Full article ">Figure 16
<p>Three-dimensional imaging results. Imaging results of space station (<b>a</b>–<b>c</b>); imaging results of satellite (<b>d</b>–<b>f</b>); and imaging results of semi-ellipsoidal object (<b>g</b>–<b>i</b>).</p> Full article ">Figure 16 Cont.
<p>Three-dimensional imaging results. Imaging results of space station (<b>a</b>–<b>c</b>); imaging results of satellite (<b>d</b>–<b>f</b>); and imaging results of semi-ellipsoidal object (<b>g</b>–<b>i</b>).</p> Full article ">Figure 17
<p>Three-dimensional imaging preprocessing results. (<b>a</b>) preprocessing result of the space station object; (<b>b</b>) preprocessing result of the satellite object; (<b>c</b>) preprocessing result of the semi-ellipsoidal object.</p> Full article ">Figure 18
<p>Three-dimensional imaging distance depth image. (<b>a</b>) distance depth image of the space station object; (<b>b</b>) distance depth image of the satellite object; (<b>c</b>) distance depth image of the semi-ellipsoidal object.</p> Full article ">Figure 19
<p>Three-dimensional imaging point cloud image. (<b>a</b>) point cloud image of the space station object; (<b>b</b>) point cloud image of the satellite object; (<b>c</b>) point cloud image of the semi-ellipsoidal object.</p> Full article ">Figure 20
<p>The target area is selected for evaluation measurements; red squares were selected for evaluation; each red square was 100 × 100 pixels.</p> Full article ">Figure 21
<p>Distance information histogram distribution, the number represents the percentage of distance x.</p> Full article ">Figure 22
<p>The target area is selected for evaluation measurements.</p> Full article ">
15 pages, 18288 KiB  
Article
Generation Mechanism of Anisotropy in Mechanical Properties of WE43 Fabricated by Laser Powder Bed Fusion
by Jingfei Bai, Qiulin Wang, Zhengxing Men, Wen Chen, Huanjie Huang, Chen Ji, Yong Li, Liang Wang, Liang Zhu, Kun Li and Qing Su
Micromachines 2024, 15(8), 976; https://doi.org/10.3390/mi15080976 - 30 Jul 2024
Viewed by 349
Abstract
At present, no consensus has been reached on the generation mechanism of anisotropy in materials fabricated by laser powder bed fusion (LPBF), and most attention has been focused on crystallographic texture. In this paper, an analysis and test were carried out on the [...] Read more.
At present, no consensus has been reached on the generation mechanism of anisotropy in materials fabricated by laser powder bed fusion (LPBF), and most attention has been focused on crystallographic texture. In this paper, an analysis and test were carried out on the hardness, defect distribution, residual stress distribution, and microstructure of WE43 magnesium alloy fabricated by LPBF. The results indicate that LPBF WE43 exhibits obvious anisotropy—the hardness HV of X–Z surface (129.9 HV on average) and that of Y–Z surface (130.7 HV on average) are about 33.5% higher than that of X–Y surface (97.6 HV on average), and the endurable load is smaller in the stacking direction Z compared to the X and Y directions. The factors contributing more to the anisotropy are listed as follows in sequence. Firstly, the defect area of the X–Y projection surface is about 13.2% larger than that of the other two surfaces, so this surface shows greatly reduced mechanical properties due to the exponential relationship between the material strength and the number of defects. Secondly, for laser scanning in each layer/time, the residual stress accumulation in the Z direction is higher than that in the X and Y directions, which may directly reduce the mechanical properties of the material. Finally, more fine grains are distributed in X–Z and Y–Z surfaces when comparing them with those in an X–Y surface, and this fine-grain strengthening mechanism also contributes to the anisotropy. After T5 aging heat treatment (250 °C/16 h), a stronger crystallographic texture is formed in the <0001> direction, with the orientation density index increasing from 10.92 to 21.38, and the anisotropy disappearing. This is mainly caused by the enhancement effect of the texture in the <0001> direction on the mechanical properties in the Z direction cancelling out the weakening effect of the defects in the X–Y surface in the Z direction. Full article
(This article belongs to the Special Issue Optical and Laser Material Processing)
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Figure 1
<p>Substrate and scanning direction co-ordinate system of LPBF.</p> Full article ">Figure 2
<p>Schematic diagram of T5 aging heat treatment process.</p> Full article ">Figure 3
<p>Microhardness HV distribution of WE43 formed by LPBF: (<b>a</b>) before aging treatment; (<b>b</b>) after T5 aging treatment.</p> Full article ">Figure 4
<p>Defects of WE43 formed by LPBF.</p> Full article ">Figure 5
<p>Testing results of void defects: (<b>a</b>) cumulative projected area of defects on each surface; (<b>b</b>) distribution of defects on Y–Z surface 5.68 mm away from axis 0 in the X direction; (<b>c</b>) distribution of defects on X–Y surface 0.88 mm away from axis 0 in the Z direction.</p> Full article ">Figure 6
<p>Schematic diagram of residual internal stress analysis of solidification molten pool: (<b>a</b>) X/Y–Z surface; (<b>b</b>) X–Y surface; (<b>c</b>) X/Y–Z surface at re-heat input.</p> Full article ">Figure 7
<p>Microstructure of WE43 formed by LPBF: (<b>a</b>) 3D morphology; (<b>b</b>) X–Y surface; (<b>c</b>) X–Z surface; (<b>d</b>) Y–Z surface.</p> Full article ">Figure 8
<p>Microstructure of molten pool.</p> Full article ">Figure 9
<p>Microstructure after T5 aging treatment; (<b>b</b>) representing the enlarged view of zone A in (<b>a</b>).</p> Full article ">Figure 10
<p>EBSD testing results of WE43 formed by LPBF: (<b>a</b>) grain morphology; (<b>b</b>) grain size statistics; (<b>c</b>) pole figure; (<b>d</b>) inverse pole figure.</p> Full article ">Figure 11
<p>EBSD testing results of the WE43 sample formed by LPBF after T5 aging treatment: (<b>a</b>) grain morphology; (<b>b</b>) grain size statistics; (<b>c</b>) pole figure; (<b>d</b>) inverse pole figure.</p> Full article ">Figure 12
<p>Schematic diagram of grain growth change: (<b>a</b>) Initial grain of LPBF WE43; (<b>b</b>) Growing grains after T5 aging treatment.</p> Full article ">
15 pages, 2770 KiB  
Article
Prediction of Geometric Characteristics of Laser Cladding Layer Based on Least Squares Support Vector Regression and Crested Porcupine Optimization
by Xiangpan Li, Junfei Xu, Junhua Wang, Yan Lu, Jianhai Han, Bingjing Guo and Tancheng Xie
Micromachines 2024, 15(7), 919; https://doi.org/10.3390/mi15070919 - 16 Jul 2024
Viewed by 455
Abstract
The morphology size of laser cladding is a crucial parameter that significantly impacts the quality and performance of the cladding layer. This study proposes a predictive model for the cladding morphology size based on the Least Squares Support Vector Regression (LSSVR) and the [...] Read more.
The morphology size of laser cladding is a crucial parameter that significantly impacts the quality and performance of the cladding layer. This study proposes a predictive model for the cladding morphology size based on the Least Squares Support Vector Regression (LSSVR) and the Crowned Porcupine Optimization (CPO) algorithm. Specifically, the proposed model takes three key parameters as inputs: laser power, scanning speed, and powder feeding rate, with the width and height of the cladding layer as outputs. To further enhance the predictive accuracy of the LSSVR model, a CPO-based optimization strategy is applied to adjust the penalty factor and kernel parameters. Consequently, the CPO-LSSVR model is established and evaluated against the LSSVR model and the Genetic Algorithm-optimized Backpropagation Neural Network (GA-BP) model in terms of relative error metrics. The experimental results demonstrate that the CPO-LSSVR model can achieve a significantly improved relative error of no more than 2.5%, indicating a substantial enhancement in predictive accuracy compared to other methods and showcasing its superior predictive performance. The high accuracy of the CPO-LSSVR model can effectively guide the selection of laser cladding process parameters and thereby enhance the quality and efficiency of the cladding process. Full article
(This article belongs to the Special Issue Optical and Laser Material Processing)
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<p>Schematic diagram of the laser cladding system.</p> Full article ">Figure 2
<p>Cross-section of the cladding layer. (<b>a</b>) The schematic diagram; (<b>b</b>) the sample.</p> Full article ">Figure 3
<p>Crested porcupine optimization algorithm flowchart.</p> Full article ">Figure 4
<p>Flowchart of CPO algorithm optimization for LSSVR model.</p> Full article ">Figure 5
<p>Comparison of the actual values of the test set with the predicted values of LSSVR. (<b>a</b>) Graph of actual width values compared to predicted width values. (<b>b</b>) Graph of actual height values compared to predicted height values.</p> Full article ">Figure 6
<p>Diagram of the GA-BP process.</p> Full article ">Figure 7
<p>Comparison of overlay width prediction performance among different models. (<b>a</b>) Comparison of predicted values from different models. (<b>b</b>) Comparison of relative errors among different models.</p> Full article ">Figure 8
<p>Comparison of overlay height prediction performance among different models. (<b>a</b>) Comparison of predicted values from different models. (<b>b</b>) Comparison of relative errors among different models.</p> Full article ">
10 pages, 6156 KiB  
Article
Accurate Detection and Analysis of Pore Defects in Laser Powder Bed Fusion WE43 Magnesium Alloys
by Zhengxing Men, Liang Wang, Xi Gao, Wen Chen, Chen Ji, Ziche Li and Kun Li
Micromachines 2024, 15(7), 909; https://doi.org/10.3390/mi15070909 - 12 Jul 2024
Viewed by 478
Abstract
To explore the size, morphology, and distribution patterns of internal pore defects in WE43 magnesium alloy formed by laser powder bed fusion (LPBF), as well as their impact on its mechanical properties, computer tomography (CT), metallographic microscopy, and scanning electron microscopy were used [...] Read more.
To explore the size, morphology, and distribution patterns of internal pore defects in WE43 magnesium alloy formed by laser powder bed fusion (LPBF), as well as their impact on its mechanical properties, computer tomography (CT), metallographic microscopy, and scanning electron microscopy were used to observe the material’s microstructure and the morphology of tensile test fractures. The study revealed that a large number of randomly distributed non-circular pore defects exist internally in the LPBF-formed WE43 magnesium alloy, with a defect volume fraction of 0.16%. Approximately 80% of the defects had equivalent diameters concentrated in the range of 10∼40 μm, and 56.2% of the defects had sphericity values between 0.65∼0.7 μm, with the maximum defect equivalent diameter being 122 μm. There were a few spherical pores around 20 μm in diameter in the specimens, and unfused powder particles were found in pore defects near the edges of the parts. Under the test conditions, the fusion pool structure of LPBF-formed WE43 magnesium alloy resembled a semi-elliptical shape with a height of around 66 μm, capable of fusion three layers of powder material in a single pass. Columnar grains formed at the edge of individual fusion pools, while the central area exhibited equiaxed grains. The “scale-like pattern” formed by overlapping fusion pool structures resulted in the microstructure of LPBF-formed WE43 magnesium alloy mainly consisting of fine equiaxed grains with a size of 2.5 μm and columnar grains distributed in a band-like manner. Full article
(This article belongs to the Special Issue Optical and Laser Material Processing)
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Figure 1
<p>WE43 magnesium alloy tensile specimen. (<b>a</b>) Size of WE43 tensile sample formed by LPED. (<b>b</b>) Sample physical object. (<b>c</b>) Mesh partitioning for finite element analysis.</p> Full article ">Figure 2
<p>CT inspection results of LPBF-formed WE43 magnesium alloy. (<b>a</b>) Pore defects with an equivalent diameter of 10 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m and larger. (<b>b</b>) Pore defects with an equivalent diameter in the range of 77 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m to 122 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m. (<b>c</b>) Pore defects with an equivalent diameter of 122.235 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m. Its sphericity is measured at 0.6, resembling a horn-like morphology in (<b>d</b>).</p> Full article ">Figure 3
<p>XY Cross-sectional CT Inspection Results of Tensile Specimen. (<b>a</b>) 2.37 mm from the bottom surface. (<b>b</b>) 9.54 mm from the bottom surface. (<b>c</b>) 15.43 mm from the bottom surface. (<b>d</b>) 19.14 mm from the bottom surface.</p> Full article ">Figure 4
<p>ZX and YZ cross-sectional CT inspection results of tensile specimen. (<b>a</b>) Parallel to the ZX plane and 0.58 mm away from the side. (<b>b</b>) Parallel to the ZX plane and 1.58 mm away from the side. (<b>c</b>) Parallel to the ZY plane and 1.12 mm away from the side. (<b>d</b>) Parallel to the ZY plane and 2.44 mm away from the side.</p> Full article ">Figure 5
<p>Distribution and normal distribution curve of defect sizes in WE43 magnesium alloy.</p> Full article ">Figure 6
<p>Sphericity and normal distribution curve distribution of defects in WE43 magnesium alloy.</p> Full article ">Figure 7
<p>Appearance of WE43 prepared by LPBF. (<b>a</b>) Specific microstructural formations along the longitudinal cross-section of the part. (<b>b</b>,<b>e</b>)Isolated defects. (<b>c</b>,<b>d</b>) Continuous defects.</p> Full article ">Figure 8
<p>The outer surface Fusion pool structure of WE43 prepared by LPBF.</p> Full article ">Figure 9
<p>High magnification morphology of WE43 prepared by LPBF. (<b>a</b>) Cross sectional microstructure diagram of WE43 magnesium alloy formed by LPBF after etching. (<b>b</b>) Longitudinal cross-sectional microstructure diagram of the edge of WE43 magnesium alloy specimen formed by LPBF.</p> Full article ">Figure 10
<p>Room temperature tensile curve of LPBF-formed WE43. (<b>a</b>) The room temperature tensile curve of LPBF-formed WE43 magnesium alloy. (<b>b</b>) Stress–strain curve of LPBF formed D-WE43 magnesium alloy. (<b>c</b>) Neck contraction diagram of the fracture area. (<b>d</b>,<b>e</b>) Fracture surface of WE43 magnesium alloy.</p> Full article ">
8 pages, 6566 KiB  
Communication
A 3.2 kW Single Stage Narrow Linewidth Fiber Amplifier Emitting at 1050 nm
by Xiaoxi Liu, Xin Tian, Binyu Rao, Baolai Yang, Xiaoming Xi and Zefeng Wang
Micromachines 2024, 15(7), 871; https://doi.org/10.3390/mi15070871 - 30 Jun 2024
Viewed by 652
Abstract
In this paper, we have demonstrated a narrow linewidth high power fiber laser emitting at a short wavelength of ~1050 nm. The fiber laser is based on a structure of master oscillator power amplification (MOPA) with an optimized fiber Bragg-grating-based laser cavity as [...] Read more.
In this paper, we have demonstrated a narrow linewidth high power fiber laser emitting at a short wavelength of ~1050 nm. The fiber laser is based on a structure of master oscillator power amplification (MOPA) with an optimized fiber Bragg-grating-based laser cavity as the seed. Both stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) effects have been effectively suppressed by using a long passive fiber between the seed and the amplifier. Based on the fiber amplifier, we have ultimately boosted the narrow linewidth laser from ~40 W to 3.2 kW with a slope efficiency of 85.1% and a 3-dB linewidth of ~0.1 nm. The SRS suppression ratio of the laser is ~29.7 dB at maximum power. Due to our fiber mode control strategies, the beam quality always stays near-diffraction-limited while amplifying, and the measured M2 factor is ~1.4 at the maximum power. Further increase in output power is limited by the SBS effect. Full article
(This article belongs to the Special Issue Optical and Laser Material Processing)
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Figure 1
<p>(<b>a</b>,<b>b</b>) Schematics of seed I and seed II. (<b>c</b>) Schematics of the amplifier and the YDF coiling shape. (<b>d</b>) A schematic of the measurement system.</p> Full article ">Figure 2
<p>(<b>a</b>) The output power of seed I and seed II versus pump power. (<b>b</b>) Spectra of seed I and seed II when the output power is around 42 W. Inserted: zoom in of the spectral peak region.</p> Full article ">Figure 3
<p>The results of MOPA under the situation of seed I. (<b>a</b>) Output power and O-O efficiency under a different pump; (<b>b</b>) Spectrum at the maximum output.</p> Full article ">Figure 4
<p>Output characteristics of the amplifier in the case of seed II. (<b>a</b>) Output power and O-O efficiency. (<b>b</b>) Spectrum measured with a multi-mode patch cord. (<b>c</b>) Backward power evolution in the case of the two seeds. (<b>d</b>) Measured beam quality under different output powers. Inserts: beam profiles at their beam waists.</p> Full article ">Figure 5
<p>(<b>a</b>) Output spectrum at the maximum power in the case of seed II. (<b>b</b>) Spectral broadening tendency of the amplifier.</p> Full article ">Figure 6
<p>The comparison results of temporal stability in the case of (<b>a</b>) seed I and (<b>b</b>) seed II.</p> Full article ">Figure 7
<p>Normalization standard deviation of temporal data of seed I and seed II.</p> Full article ">
17 pages, 6962 KiB  
Article
Enhancing the Spin Hall Effect of Cylindrically Polarized Beams
by Alexey A. Kovalev, Anton G. Nalimov and Victor V. Kotlyar
Micromachines 2024, 15(3), 350; https://doi.org/10.3390/mi15030350 - 29 Feb 2024
Viewed by 912
Abstract
Two linked gear wheels in a micromachine can be simultaneously rotated in opposite directions by using a laser beam that has in its section areas the spin angular momentum (SAM) of the opposite sign. However, for instance, a cylindrical vector beam has zero [...] Read more.
Two linked gear wheels in a micromachine can be simultaneously rotated in opposite directions by using a laser beam that has in its section areas the spin angular momentum (SAM) of the opposite sign. However, for instance, a cylindrical vector beam has zero SAM in the focus. We alter a cylindrical vector beam so as to generate areas in its focus where the SAM is of opposite signs. The first alteration is adding to the cylindrical vector beam a linearly polarized beam. Thus, we study superposition of two rotationally symmetric beams: those with cylindrical and linear polarization. We obtain an expression for the SAM and prove two of its properties. The first property is that changing superposition coefficients does not change the shape of the SAM density distribution, whereas the intensity changes. The second property is that maximal SAM density is achieved when both beams in the superposition have the same energy. The second perturbation is adding a spatial carrier frequency. We study the SAM density of a cylindrical vector beam with a spatial carrier frequency. Due to periodic modulation, upon propagation in space, such a beam is split into two beams, having left and right elliptic polarization. Thus, in the beam transverse section, areas with the spin of different signs are separated in space, which is a manifestation of the spin Hall effect. We demonstrate that such light beams can be generated by metasurfaces, with the transmittance depending periodically on one coordinate. Full article
(This article belongs to the Special Issue Optical and Laser Material Processing)
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Figure 1
<p>Intensity distribution of beam (27) with <span class="html-italic">w</span> = 1 mm, <span class="html-italic">n</span> = 3, and α = 0.001<span class="html-italic">k</span> at a distance of <span class="html-italic">z</span><sub>0</sub> from the waist plane, shown by white-yellow rings (<b>a</b>), and polarization distribution over the beam transverse section, shown by ellipses (pink ellipses denote right-handed polarization <span class="html-italic">S<sub>z</sub></span> &gt; 0 and cyan ellipses denote left-handed polarization <span class="html-italic">S<sub>z</sub></span> &lt; 0); phase distribution of one transverse component of the light field <span class="html-italic">E<sub>x</sub></span> (<b>b</b>). The size of both figures is 30 × 30 mm.</p> Full article ">Figure 2
<p>Intensity (<b>a</b>–<b>e</b>) and SAM density (<b>f</b>–<b>j</b>) distributions of several superpositions of the cylindrically polarized Laguerre-Gaussian beams (30) and linearly polarized Gaussian beams (32) with different weight coefficients for the following parameters: wavelength λ = 532 nm, Gaussian beam waist radii <span class="html-italic">w</span><sub>0</sub> = 1 mm and <span class="html-italic">w</span><sub>1</sub> = 5 mm, radial and azimuthal orders of the cylindrically polarized Laguerre-Gaussian beam <span class="html-italic">p</span> = 2 and <span class="html-italic">m</span> = 3, propagation distance from the initial plane <span class="html-italic">z</span> = <span class="html-italic">z</span><sub>0</sub>, superposition coefficients <span class="html-italic">C</span><sub>C</sub><sup>2</sup> = 0.95, <span class="html-italic">C</span><sub>L</sub><sup>2</sup> = 0.05 (<b>a</b>,<b>f</b>), <span class="html-italic">C</span><sub>C</sub><sup>2</sup> = 0.70, <span class="html-italic">C</span><sub>L</sub><sup>2</sup> = 0.30 (<b>b</b>,<b>g</b>), <span class="html-italic">C</span><sub>C</sub><sup>2</sup> = <span class="html-italic">C</span><sub>L</sub><sup>2</sup> = 0.50 (<b>c</b>,<b>h</b>), <span class="html-italic">C</span><sub>C</sub><sup>2</sup> = 0.30, <span class="html-italic">C</span><sub>L</sub><sup>2</sup> = 0.70 (<b>d</b>,<b>i</b>), and <span class="html-italic">C</span><sub>C</sub><sup>2</sup> = 0.01, <span class="html-italic">C</span><sub>L</sub><sup>2</sup> = 0.99 (<b>e</b>,<b>j</b>). The numbers near the color scales denote the minimal and maximal values.</p> Full article ">Figure 3
<p>Intensity (<b>a</b>–<b>e</b>) and SAM density (<b>f</b>–<b>j</b>) distributions of several superpositions of the cylindrically polarized Bessel-Gaussian beams (34) and linearly polarized difference of two Gaussian beams (36) with different weight coefficients for the following parameters: wavelength λ = 532 nm, waist radius of the Gaussian envelope of the Bessel-Gaussian beam <span class="html-italic">w</span><sub>0</sub> = 1 mm, scaling factor α<sub>0</sub> = <span class="html-italic">k</span>/1000, order of cylindrical polarization <span class="html-italic">m</span> = 5, waist radii of the subtracted linearly polarized Gaussian beams <span class="html-italic">w</span><sub>01</sub> = 5 mm and <span class="html-italic">w</span><sub>02</sub> = 7 mm (at these radii the light ring of the difference beam has the same radius as that of the Bessel-Gaussian beam), propagation distance from the initial plane <span class="html-italic">z</span> = <span class="html-italic">z</span><sub>0</sub>, superposition coefficients <span class="html-italic">C</span><sub>C</sub><sup>2</sup> = 0.95, <span class="html-italic">C</span><sub>L</sub><sup>2</sup> = 0.05 (<b>a</b>,<b>f</b>), <span class="html-italic">C</span><sub>C</sub><sup>2</sup> = 0.70, <span class="html-italic">C</span><sub>L</sub><sup>2</sup> = 0.30 (<b>b</b>,<b>g</b>), <span class="html-italic">C</span><sub>C</sub><sup>2</sup> = <span class="html-italic">C</span><sub>L</sub><sup>2</sup> = 0.50 (<b>c</b>,<b>h</b>), <span class="html-italic">C</span><sub>C</sub><sup>2</sup> = 0.30, <span class="html-italic">C</span><sub>L</sub><sup>2</sup> = 0.70 (<b>d</b>,<b>i</b>), and <span class="html-italic">C</span><sub>C</sub><sup>2</sup> = 0.01, <span class="html-italic">C</span><sub>L</sub><sup>2</sup> = 0.99 (<b>e</b>,<b>j</b>). The numbers near the color scales denote the minimal and maximal values.</p> Full article ">Figure 4
<p>Direction of linear polarization in the light field of (19).</p> Full article ">Figure 5
<p>Binary metasurface relief.</p> Full article ">Figure 6
<p>Intensity (<b>a</b>) and polarization distribution (<b>b</b>) of the electric field at the distance λ from the metasurface.</p> Full article ">Figure 7
<p>Intensity of light at a distance of 50.633 μm from the metasurface as well as the polarization distribution. Arrows with circles indicate polarization direction in the center of each circle, and the arrow shows the rotation direction of the vector electric field with time.</p> Full article ">Figure 8
<p>Metasurface, generating the cylindrical vector beam (27) with spatial carrier frequency (<b>a</b>), and polarization of a plane linearly polarized wave passed through this metasurface at a distance λ from it (<b>b</b>).</p> Full article ">Figure 9
<p>Intensity of the cylindrical vector beam with the carrier frequency, generated by the metalens, and polarization of this beam, depicted as ellipses with arrows (<b>a</b>), as well as the phase of the <span class="html-italic">E<sub>y</sub></span> field component (<b>b</b>). Each ellipse (<b>a</b>) describes rotation of the electric field vector with time.</p> Full article ">
12 pages, 8869 KiB  
Article
Hydrophobic Surface Array Structure Based on Laser-Induced Graphene for Deicing and Anti-Icing Applications
by Mian Zhong, Shichen Li, Yao Zou, Hongyun Fan, Yong Jiang, Chao Qiu, Jinling Luo and Liang Yang
Micromachines 2024, 15(2), 285; https://doi.org/10.3390/mi15020285 - 17 Feb 2024
Cited by 12 | Viewed by 1311
Abstract
The exceptional performance of graphene has driven the advancement of its preparation techniques and applications. Laser-induced graphene (LIG), as a novel graphene preparation technique, has been applied in various fields. Graphene periodic structures created by the LIG technique exhibit superhydrophobic characteristics and can [...] Read more.
The exceptional performance of graphene has driven the advancement of its preparation techniques and applications. Laser-induced graphene (LIG), as a novel graphene preparation technique, has been applied in various fields. Graphene periodic structures created by the LIG technique exhibit superhydrophobic characteristics and can be used for deicing and anti-icing applications, which are significantly influenced by the laser parameters. The laser surface treatment process was simulated by a finite element software analysis (COMSOL Multiphysics) to optimize the scanning parameter range, and the linear array surface structure was subsequently fabricated by the LIG technique. The generation of graphene was confirmed by Raman spectroscopy and energy-dispersive X-ray spectroscopy. The periodic linear array structure was observed by scanning electron microscopy (SEM) and confocal laser imaging (CLSM). In addition, CLSM testings, contact angle measurements, and delayed icing experiments were systematically performed to investigate the effect of scanning speed on surface hydrophobicity. The results show that high-quality and uniform graphene can be achieved using the laser scanning speed of 125 mm/s. The periodic linear array structures can obviously increase the contact angle and suppress delayed icing. Furthermore, these structures have the enhanced ability of the electric heating deicing, which can reach 100 °C and 240 °C within 15 s and within 60 s under the DC voltage power supply ranging from 3 to 7 V, respectively. These results indicate that the LIG technique can be developed to provide an efficient, economical, and convenient approach for preparing graphene and that the hydrophobic surface array structure based on LIG has considerable potential for deicing and anti-icing applications. Full article
(This article belongs to the Special Issue Optical and Laser Material Processing)
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Figure 1
<p>Preparation flow chart of LIG hydrophobic surface.</p> Full article ">Figure 2
<p>(<b>a</b>–<b>c</b>) Finite element simulation results of the PI surface directly written using a CO<sub>2</sub> laser between temperature trend and surface treatment time: positive temperature, negative temperature, and heat stress. The illustrations are as follows: (<b>a</b>) front picture of sample; (<b>b</b>) backside view of sample; (<b>c</b>) simulated stress distribution map during halfway scan; (<b>d</b>–<b>h</b>) SEM images of LIG arrays at scanning speeds of 50, 75, 100, 125, and 150 mm/s, scale bar: 500 μm, 200 μm, 50 μm; (<b>i</b>) Raman spectra of the LIG array surface at scanning speeds of 100, 125, and 150 mm/s.</p> Full article ">Figure 3
<p>(<b>a</b>–<b>c</b>) CLSM test diagram of the graphene linear array surface at scanning speeds of 100, 125, and 150 mm/s. (<b>d</b>,<b>e</b>) EDS test diagram of the graphene linear array surface on PI film at a scanning speed of 125 mm/s, scale bar: 500 μm.</p> Full article ">Figure 4
<p>Surface hydrophobicity of graphene linear array at scanning speeds of 100, 125, 150 mm/s: (<b>a</b>–<b>c</b>) side views of the surface WCA; (<b>d</b>) surface WCA and surface energy; (<b>e</b>–<b>g</b>) 2D height maps of surfaces; (<b>h</b>) surface roughness and line height.</p> Full article ">Figure 5
<p>Schematic and mechanism of delayed icing effect on graphene linear array surface at low temperatures: (<b>a</b>–<b>d</b>) the corresponding time of the initial state of the droplet on the surface and the beginning of ice core and complete icing at scanning speeds of 100, 125, and 150 mm/s; (<b>e</b>) comparison of delayed icing effect and delayed icing mechanism in terms of time.</p> Full article ">Figure 6
<p>Laser-induced electrothermal properties of graphene surface at scanning speeds of 100, 125, and 150 mm/s: (<b>a</b>) square resistance of graphene linear array surface; (<b>b</b>) electrothermal connection method and power consumption of graphene surface; (<b>c</b>) electrothermal steady-state temperature at a voltage of 3–7 V; (<b>d</b>–<b>f</b>) trend chart of electric heating temperature change on the surface at different voltage values; (<b>g</b>–<b>i</b>) infrared thermal imaging map corresponding to the surface electrothermal steady-state temperature.</p> Full article ">
12 pages, 2144 KiB  
Article
Selective CW Laser Synthesis of MoS2 and Mixture of MoS2 and MoO2 from (NH4)2MoS4 Film
by Noah Hurley, Bhojraj Bhandari, Steve Kamau, Roberto Gonzalez Rodriguez, Brian Squires, Anupama B. Kaul, Jingbiao Cui and Yuankun Lin
Micromachines 2024, 15(2), 258; https://doi.org/10.3390/mi15020258 - 9 Feb 2024
Cited by 1 | Viewed by 1021
Abstract
Very recently, the synthesis of 2D MoS2 and WS2 through pulsed laser-directed thermolysis can achieve wafer-scale and large-area structures, in ambient conditions. In this paper, we report the synthesis of MoS2 and MoS2 oxides from (NH4)2 [...] Read more.
Very recently, the synthesis of 2D MoS2 and WS2 through pulsed laser-directed thermolysis can achieve wafer-scale and large-area structures, in ambient conditions. In this paper, we report the synthesis of MoS2 and MoS2 oxides from (NH4)2MoS4 film using a visible continuous-wave (CW) laser at 532 nm, instead of the infrared pulsed laser for the laser-directed thermolysis. The (NH4)2MoS4 film is prepared by dissolving its crystal powder in DI water, sonicating the solution, and dip-coating onto a glass slide. We observed a laser intensity threshold for the laser synthesis of MoS2, however, it occurred in a narrow laser intensity range. Above that range, a mixture of MoS2 and MoO2 is formed, which can be used for a memristor device, as demonstrated by other research groups. We did not observe a mixture of MoS2 and MoO3 in the laser thermolysis of (NH4)2MoS4. The laser synthesis of MoS2 in a line pattern is also achieved through laser scanning. Due to of the ease of CW beam steering and the fine control of laser intensities, this study can lead toward the CW laser-directed thermolysis of (NH4)2MoS4 film for the fast, non-vacuum, patternable, and wafer-scale synthesis of 2D MoS2. Full article
(This article belongs to the Special Issue Optical and Laser Material Processing)
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<p>(<b>a</b>) Raman spectra at laser power 0.3 mW from ATM crystal (grey line) and from thermally annealed one (blue line) at 500 <math display="inline"><semantics> <mrow> <mo>°</mo> <mi mathvariant="normal">C</mi> </mrow> </semantics></math> for 30 min. (<b>b</b>) Raman spectra of different Raman modes at laser power 0.3 mW from MoS<sub>2</sub> converted from ATM after annealing, at three different positions. (<b>c</b>) Comparison of XRD from ATM crystals before and after thermal annealing at 500 <math display="inline"><semantics> <mrow> <mo>°</mo> <mi mathvariant="normal">C</mi> </mrow> </semantics></math> for 30 min.</p> Full article ">Figure 2
<p>(<b>a</b>) Comparison of Raman spectra at laser power 0.3 mW from ATM film and its annealed sample. (<b>b</b>) PL measurement for 2D exfoliated MoS<sub>2</sub> under 10 mW and annealed sample from ATM film at laser power of 0.3 mW.</p> Full article ">Figure 3
<p>(<b>a</b>) Raman spectra from the same location of ATM crystal under laser power 0.3, 0.5, 1, 2, 3, and 4 mW. (<b>b</b>) Raman spectra from the same location of ATM crystal under laser power 0.3, 0.5, and 0.8 mW. (<b>c</b>) Raman spectra from the same location of ATM crystal under laser power 0.8 mW and 1 mW.</p> Full article ">Figure 4
<p>(<b>a</b>,<b>b</b>) Raman spectra under laser power from non-dark region (<b>a</b>) and dark spot ((<b>b</b>), image in inset) in exfoliated 2D multilayer MoS<sub>2</sub> annealed at 420 °C for 30 min in the atmosphere. (<b>c</b>) Raman spectra from exfoliated 2D multilayer MoSe<sub>2</sub> under laser power of 2.5 mW (light-blue line) and 25 mW (black line). (<b>d</b>,<b>e</b>) Raman spectra from exfoliated 2D multilayer MoS<sub>2</sub> measured at 0.5 mW after exposed to a laser power of 50 mW for 2 min (<b>d</b>) and measured directly under a laser power of 50 mW (<b>e</b>). (<b>f</b>) PL of exfoliated 2D multilayer MoS<sub>2</sub> after exposure to a laser power of 50 mW for 2 min.</p> Full article ">Figure 5
<p>(<b>a</b>) Raman spectra from different ATM film locations under a laser power of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, and 4 mW. (<b>b</b>) Raman spectra from different ATM locations under a laser power of 4, 4.5, 5, and 5.5 mW. (<b>c</b>) Raman spectra from different ATM film locations under a laser power of 6, 6.5, 8, 10, 12, 14, 16, and 18 mW. Inset is the Raman spectrum under a laser power of 18 mW after the spectrum of glass is subtracted. (<b>d</b>) Positions of A<sub>1g</sub> and E<sub>2g</sub> modes that appear from ATM film under different laser power.</p> Full article ">Figure 6
<p>(<b>a</b>) Raman spectra from the same ATM film location under a laser power of 2, 3, 4.5, 6, 7.5, 9, 10, and 10.5 mW. (<b>b</b>) Raman spectra from the same ATM film location under a laser power of 11, 12.5, 14, 15.5, and 17 mW. (<b>c</b>) Raman spectra from the same ATM film location under a laser power of 11 mW after the normalized spectrum of glass is subtracted.</p> Full article ">Figure 7
<p>(<b>a</b>) Optica microscope image of a line pattern across an ATM film region (white area). (<b>b</b>) Raman mapping of the line pattern produced by the laser direct writing using a laser power of 1 mW and integration time of 10 s. (<b>c</b>) Scanning electron microscope image of the line pattern.</p> Full article ">

Review

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25 pages, 7368 KiB  
Review
Advances in Laser Powder Bed Fusion of Tungsten, Tungsten Alloys, and Tungsten-Based Composites
by Hua Li, Yun Shen, Xuehua Wu, Dongsheng Wang and Youwen Yang
Micromachines 2024, 15(8), 966; https://doi.org/10.3390/mi15080966 - 28 Jul 2024
Viewed by 723
Abstract
In high-tech areas such as nuclear fusion, aerospace, and high-performance tools, tungsten and its alloys are indispensable due to their high melting point, low thermal expansion, and excellent mechanical properties. The rise of Additive Manufacturing (AM) technologies, particularly Laser Powder Bed Fusion (L-PBF), [...] Read more.
In high-tech areas such as nuclear fusion, aerospace, and high-performance tools, tungsten and its alloys are indispensable due to their high melting point, low thermal expansion, and excellent mechanical properties. The rise of Additive Manufacturing (AM) technologies, particularly Laser Powder Bed Fusion (L-PBF), has enabled the precise and rapid production of complex tungsten parts. However, cracking and densification remain major challenges in printing tungsten samples, and considerable efforts have been made to study how various processing conditions (such as laser power, scanning strategy, hatch spacing, scan speed, and substrate preheating) affect print quality. In this review, we comprehensively discuss various critical processing parameters and the impact of oxygen content on the control of the additive manufacturing process and the quality of the final parts. Additionally, we introduce additive manufacturing-compatible W materials (pure W, W alloys, and W-based composites), summarize the differences in their mechanical properties, densification, and microstructure, and further provide a clear outlook for developing additive manufactured W materials. Full article
(This article belongs to the Special Issue Optical and Laser Material Processing)
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<p>Schematic diagram of the L-PBF system working principle [<a href="#B43-micromachines-15-00966" class="html-bibr">43</a>,<a href="#B44-micromachines-15-00966" class="html-bibr">44</a>,<a href="#B45-micromachines-15-00966" class="html-bibr">45</a>,<a href="#B46-micromachines-15-00966" class="html-bibr">46</a>].</p> Full article ">Figure 2
<p>The crack distribution on the top surface of pure tungsten. (<b>a</b>) the raw surface morphology, (<b>b</b>) the crack distribution and (<b>c</b>) the EBSD of pure W [<a href="#B75-micromachines-15-00966" class="html-bibr">75</a>].</p> Full article ">Figure 3
<p>SEM micrographs of the top view of pure W samples prepared by L-PBF: (<b>a</b>–<b>f</b>) nanopores formed in the as-built samples [<a href="#B89-micromachines-15-00966" class="html-bibr">89</a>].</p> Full article ">Figure 4
<p>Common types of scanning strategies [<a href="#B100-micromachines-15-00966" class="html-bibr">100</a>,<a href="#B101-micromachines-15-00966" class="html-bibr">101</a>].</p> Full article ">Figure 5
<p>Band contrast (BC) maps showing grain structure of the (<b>a</b>) SS-X and (<b>b</b>) SS-XY specimens from the YZ cross section, insets in (<b>a</b>,<b>b</b>): pole figures of the SS-X and SS-XY specimens, respectively, high-magnification SEM backscatter electron images of the dendrite structure of the (<b>c</b>) SS-X and (<b>d</b>) SS-XY specimens [<a href="#B106-micromachines-15-00966" class="html-bibr">106</a>].</p> Full article ">Figure 6
<p>Schematic of pure W nanostructure formation in the laser melt pool: (<b>a1</b>) liquid state in the laser melt pool; (<b>a2</b>) W matrix begins to solidify; (<b>a3</b>) gas captured in the W matrix during boiling; (<b>a4</b>) nanoscale pores formed at room temperature [<a href="#B75-micromachines-15-00966" class="html-bibr">75</a>]. (<b>b</b>) SEM images showing nanoscale pores in pure W [<a href="#B75-micromachines-15-00966" class="html-bibr">75</a>]. (<b>c</b>) Oxidation mechanism diagram and quantified kinetics of pure W in the temperature range of 600–1600 °C [<a href="#B114-micromachines-15-00966" class="html-bibr">114</a>].</p> Full article ">Figure 7
<p>(<b>a</b>,<b>d</b>) the raw surface morphology, (<b>b</b>,<b>e</b>) the crack distribution, and the (<b>c</b>,<b>f</b>) EBSD of pure W and W-6Ta [<a href="#B75-micromachines-15-00966" class="html-bibr">75</a>].</p> Full article ">Figure 8
<p>Microstructure of SLM-fabricated W–Ni samples: (<b>a</b>) Ni content of 10%; (<b>b</b>) Ni content of 20%; (<b>c</b>) Ni content of 40% [<a href="#B55-micromachines-15-00966" class="html-bibr">55</a>].</p> Full article ">Figure 9
<p>(<b>a</b>,<b>c</b>) show the grain boundary lines corresponding to the IPF maps, with red and blue lines representing LAGB and HAGB, respectively. (<b>b</b>,<b>d</b>) are histograms of the misorientation angle data [<a href="#B120-micromachines-15-00966" class="html-bibr">120</a>].</p> Full article ">Figure 10
<p>IPF maps of pure W and W-Re alloys. (<b>a</b>–<b>d</b>) are horizontal cross-sections; (<b>e</b>–<b>h</b>) are vertical cross-sections [<a href="#B120-micromachines-15-00966" class="html-bibr">120</a>].</p> Full article ">Figure 11
<p>Analysis of the nanoparticles. (<b>a</b>) is bright field image showing the distribution of the nanoparticles, (<b>b</b>) is the HRTEM of the selected nanoparticle, (<b>c</b>) is the high-angle annular dark field (HAADF) image. (<b>d</b>,<b>e</b>,<b>g</b>,<b>h</b>) are the EDS maps of the selected nanoparticle at a different magnification and (<b>f</b>) is the SAEDP of the selected nanoparticle [<a href="#B126-micromachines-15-00966" class="html-bibr">126</a>].</p> Full article ">
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