There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Preface.Introduction.Chapter 1. Selected Topics in Electromagnetic Wave Propagation.1.1. Maxwell's Equations and the Fundamental Fields.1.2. Electromagnetic Wave Propagation in Sourceless Media.1.3. Power Transmission.1.4. Group Velocity.1.5. Reflection and Transmission of Waves at Plane Interfaces.1.6. Material Resonances and Their Effects on Wave Propagation.Problems.References.Chapter 2. Symmetric Dielectric Slab Waveguides.2.1. Ray Analysis of the Slab Waveguides.2.2. Field Analysis of the Slab Waveguides.2.3. Solutions of the Eigenvalue Equations.2.4. Power Transmission and Confinement.2.5. Leaky Waves.2.6. Radiation Modes.2.7. Wave Propagation in Curved Slab Waveguides.Problems.References.Chapter 3. Weakly-Guiding Fibers with Step Index Profiles.3.1. Rays and Fields in the Step Index Fiber.3.2. Field Analysis of the Weakly-Guiding Fiber.3.3. Eigenvalue Equation for LP Modes.3.4. LP Mode Characteristics.3.5. Single Mode Fiber Parameters.3.6. Derivation of the General Step Index Fiber Modes.Problems.References.Chapter 4. Loss Mechanisms in Silica Fiber.4.1. Basic Loss Effects in Transmission.4.2. Fabrication of Silica Fibers.4.3. Intrinsic Loss.4.4. Extrinsic Loss.4.5. Bending Loss.4.6. Source-to-Fiber Coupling.Problems.References.Chapter 5. Dispersion.5.1. Pulse Propagation in Media Possessing Quadratic Dispersion.5.2. Material Dispersion.5.3. Dispersion in Optical Fiber.5.4. Chromatic Dispersion Compensation.5.5. Polarization Dispersion.5.6. System Considerations and Dispersion Measurement.Problems.References.Chapter 6. Special Purpose Index Profiles.6.1. Multimode Graded Index Fiber.6.2. Special Index Profile Optimization.Problems.References.Chapter 7. Nonlinear Effects in Fibers I: Non-Resonant Processes.7.1. Nonlinear Optics Fundamentals.7.2. Nonlinear Phase Modulation on Pulses.7.3. The Nonlinear Schrodinger Equation.7.4. Additional Non-Resonant Processes.Problems.References.Chapter 8. Nonlinear Effects in Fibers II: Resonant Processes and Amplification.8.1. Raman Scattering.8.2. Stimulated Brillouin Scattering.8.3. Rare-Earth-Doped Fiber Amplifiers.Problems.References.Appendix A: Properties of Bessel Functions.Appendix B: Notation.Index.

Fundamentals of optical fibers

Analysis of crack behavior for Ni-based WC composite coatings by laser cladding and crack-free realization

The use of magnesium alloys as degradable metals for biomedical applications is a topic of ongoing research and the demand for multifunctional materials is increasing. Hence, binary Mg-Ag alloys were designed as implant materials to combine the favourable properties of magnesium with the well-known antibacterial property of silver. In this study, three Mg-Ag alloys, Mg2Ag, Mg4Ag and Mg6Ag that contain 1.87 %, 3.82 % and 6.00 % silver by weight, respectively, were cast and processed with solution (T4) and aging (T6) heat treatment. The metallurgical analysis and phase identification showed that all alloys contained Mg4Ag as the dominant β phase. After heat treatment, the mechanical properties of all Mg-Ag alloys were significantly improved and the corrosion rate was also significantly reduced, due to presence of silver. Mg(OH)₂ and MgO present the main magnesium corrosion products, while AgCl was found as the corresponding primary silver corrosion product. Immersion tests, under cell culture conditions, demonstrated that the silver content did not significantly shift the pH and magnesium ion release. In vitro tests, with both primary osteoblasts and cell lines (MG63, RAW 264.7), revealed that Mg-Ag alloys show negligible cytotoxicity and sound cytocompatibility. Antibacterial assays, performed in a dynamic bioreactor system, proved that the alloys reduce the viability of two common pathogenic bacteria, Staphylococcus aureus (DSMZ 20231) and Staphylococcus epidermidis (DSMZ 3269), and the results showed that the killing rate of the alloys against tested bacteria exceeded 90%. In summary, biodegradable Mg-Ag alloys are cytocompatible materials with adjustable mechanical and corrosion properties and show promising antibacterial activity, which indicates their potential as antibacterial biodegradable implant materials.

/pdf/antibacterial-biodegradable-mg-ag-alloys-omtyjgv8dj.pdf

Antibacterial biodegradable Mg-Ag alloys

Laser cladding is a process whereby a new layer of material is deposited on a substrate by laser fusion of blown powders or pre-placed powder coatings. Multiple layers can be deposited to form shapes with complex geometry. This manufacturing process has been used for material surface property modification and for the repair and manufacture of three-dimensional components. Laser cladding has attracted extensive research over the past 30 years. Over 2000 research papers have been published in journals and international conferences. Research in laser cladding covers many scientific issues, including processing techniques, physical and chemical properties of deposited materials and clad—substrate interfaces, microstructure and phases, rapid solidification phenomena, modelling and simulation, and systems engineering and applications. This article, focusing on the rapid heating/cooling processes and material response, summarizes the state of the art on two fundamental scientific aspects: rapid solidific...

Laser surface cladding: The state of the art and challenges

Laser cladding is an advanced material processing technology that has potential to deposit various materials locally on highly non-planar and complex surfaces. It can be used to refurbish or improve corrosion, wear and other surface related properties of components. The laser cladding of WC–Co using continuous wave (CW) laser has been tried and problems, like—cracks, porosity, poor bonding, partial melting of WC particles in the Co matrix, etc., have been observed. To resolve these issues, the successful laser cladding with alternate binder materials, like—Ni, Fe, Co–Cr, Ni–B–Si, etc., have been reported. In the present study, a pulsed Nd:YAG laser was used to deposit multi-layer overlapped cladding on low carbon steel substrate using dynamic powder blowing technique. Thus, produced laser cladding samples were subjected to various mechanical tests and metallurgical analyses. The results showed that fully dense and crack free clad surfaces of WC–Co with an excellent metallurgical bonding and low dilution were deposited. No melting of WC particles in the Co matrix was observed during the microscopy. The average microhardness at the clad surface was about 1350 HV, while that at substrate was 200 HV. The observed adhesion strength of the WC–Co cladding to the substrate was about 60 MPa.

Cladding of WC–12 Co on low carbon steel using a pulsed Nd:YAG laser

A superstructure fiber Bragg gratings (FBG) by laser-assisted direct writing of on-fiber metallic films. A laser direct write method is used to fabricate periodic films of silver nanoparticles on the non-planar surface of as-fabricated FBGs. Silver films with a thickness of about 9 μm are fabricated around a Bragg grating optical fiber. The performance of the superstructure FBG is studied by applying temperature and tensile stress on the fiber. An opto-mechanical model is also developed to predict the optical response of the synthesized superstructure FBG under thermal and structural loadings. The reflectivity of sidebands in the reflection spectrum can be tuned up to 20% and 37% under thermal and structural loadings, respectively. In addition, the developed superstructure FBG is used for simultaneous measurement of multiple criteria such as force and temperature to eliminate the inherent limitation of regular FBGs in multi-parameter sensing.

Optical fibre sensor and methods of manufacture

This paper describes laser-based layered manufacturing processes for embedding optical fiber Bragg gratings (FBGs) in metal structures to develop cutting tools with embedded sensors. FBG is a type of optical fiber that is used for the measurement of parameters manifesting as the changes of strain or temperature. The unique features of FBGs have encouraged their widespread use in structural measurements, failure diagnostics, thermal measurements, pressure monitoring, etc. Considering the unique features of FBGs, embedding of the sensors in metal parts for in-situ load monitoring is a cutting-edge research topic with a variety of applications in machining tools, aerospace, and automotive industries. The metal embedding process is a challenging task, as the thermal decay of UV-written gratings can start at a temperature of � 200 � C and accelerates at higher temperatures. The embedding process described in this paper consists of low temperature laser microdeposition of on-fiber silver thin films followed by nickel electroplating in a steel part. A microscale laser-based direct write (DW) method, called laser-assisted maskless microdeposition (LAMM), is employed to deposit silver thin films on optical fibers. To attain thin films with optimum quality, a characterization scheme is designed to study the geometrical, mechanical, and microstructural properties of the thin films in terms of the LAMM process parameters. To realize the application of embedded FBG sensors in machining tools, the electroplating process is followed by the deposition of a layer of tungsten carbide-cobalt (WC-Co) by using laser solid freeform fabrication (LSFF). An optomechanical model is also developed to predict the optical response of the embedded FBGs. The performance of the embedded sensor is evaluated in a thermal cycle. The results show that the sensor attains its linear behavior after embedding. Microscopic analysis of the tool with the embedded sensor clearly exhibits the integrity of the deposited layers without cracks, porosity, and delamination. [DOI: 10.1115/1.4004203]

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Metal Embedded Optical Fiber Sensors: Laser-Based Layered Manufacturing Procedures

Laser cladding of a Co–Ti alloy on a mild steel substrate is studied. Premixed powders with the composition of 85 wt% cobalt and 15 wt% titanium are pre-placed on the substrate and a moving laser beam at different velocities is used to produce clad layers well bounded to the substrate. Characteristics of the clad are investigated using optical microscopy, X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and microhardness tests. The results reveal that the intermetallic phase TiCo 3 and β (i.e. fcc) cobalt are formed in the clad layer. The clad layer can also have major dilution from the substrate depending on the laser scanning velocity. It is observed that a finer microstructure is achievable with higher laser velocities whereas higher hardness is achieved using lower velocities. The latter is due to the formation of a larger fraction of TiCo 3 phase.

Deposition of Co–Ti alloy on mild steel substrate using laser cladding

In this paper, the morphology and microstructure of silver micro-lines fabricated by laser-assisted maskless microdeposition (LAMM) are investigated. In LAMM technology, suspensions of silver nano-particles are used for layer-by-layer deposition and laser post-sintering. One of the major issues in LAMM is the large number of parameters involved in the process, which in turn results in a challenging process optimization. To address this issue, a design of experiments (DOE) method is used. The topography of the sintered samples was investigated using scanning electron microscopy (SEM) and white light interferometry. The results of DOE show that the deposition flow rate and the deposition scanning speed can significantly affect the width of the fabricated patterns, while the deposition thickness is mostly affected by the laser power and the number of deposited layers. In the microstructural analysis, it is observed that high laser effective energies can increase the densification of the sintered layers, in which the particles are closely packed. This is also evident from the level of electrical conductivity of the sintered samples. It is shown that the conductivity of the sintered samples is increased up to 2 × 105 S m−1 by raising the laser effective energy density to 2.5 × 106 J m−3. In addition, the results of mechanical tests, performed by a nanoindentation instrument, give a hardness of 0.8 GPa and Young's modulus of 50 GPa for the samples.

https://iopscience.iop.org/article/10.1088/0960-1317/18/11/115015/pdf

Hamidreza Alemohammad

Papers

Cladding of WC–12 Co on low carbon steel using a pulsed Nd:YAG laser

Optical fibre sensor and methods of manufacture

Metal Embedded Optical Fiber Sensors: Laser-Based Layered Manufacturing Procedures

Deposition of Co–Ti alloy on mild steel substrate using laser cladding

Morphology and microstructure analysis of nano-silver thin films deposited by laser-assisted maskless microdeposition