David J. Whitehead

David J. Whitehead
The University of Manchester · School of Mechanical, Aerospace and Civil Engineering

About

67
Publications
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1,594
Citations

Publications

Publications (67)
Article
Diamond is a radiation hard material, which makes it suitable for its use in high energy physics experiments as particle detector. In order to further reduce the effects of radiation damage, the diamond detectors can be fabricated by inscribing graphitic electrodes perpendicular to the surface, the so called 3D detectors. This can be done via proce...
Article
Full-text available
A spatial light modulator (SLM) addressed with Computer Generated Holograms (CGH’s) can create structured light fields when an incident laser beam is diffracted by a phase CGH. The power handling limitations of SLMs based on a liquid crystal layer have always been of some concern. Now, with careful engineering of chip thermal management, we present...
Conference Paper
Full-text available
This paper presents methods to produce tailored light fields in the focal region of ultrashort-pulse lasers. As a proof of concept, various vector field landscapes are generated such as radial polarization, optical vortices, Bessel beams or tailored Fresnel wavefronts and used for laser material processing. An example application is demonstrated wh...
Article
Full-text available
Spatial light modulators (SLMs) addressed with computer generated holograms (CGHs) can create structured light fields on demand when an incident laser beam is diffracted by a phase CGH. The power handling limitations of these devices based on a liquid crystal layer has always been of some concern. With careful engineering of chip thermal management...
Research
Performance of LCOS phase only Spatial Light Modulator exposed to high average power picosecond radiation. The phase response was measured, showing that the cooled device phase reaches 2pi only below 130W, reducing to pi around 200W. Chip temperature rises linearly with power, yielding a 5degree rise with 220W exposure
Chapter
There is an urgent and growing need to reduce the environmental footprints of products and manufacturing processes and to support sustainable material consumption. For engineering applications, this implies the need to develop low energy/carbon footprint manufacturing processes that utilise extended-life tooling. In mechanical machining, nanostruct...
Article
Full-text available
Laser surface texturing or micro/nano surface structuring in the air has been extensively studied. However, until now, there are very few studies on the characteristics of laser-textured surfaces in water, and there was no reported work on picosecond laser surface micro/nano-structuring in water. In this work, the surface properties of picosecond l...
Article
The availability of ultra-short laser pulse sources such as picosecond lasers makes it possible to improve the quality (e.g. heat affected zone < 10 μm) in laser machining engineering materials such as metals and carbon fibre reinforced polymer (CFRP) composites. However, the processing rate and the machining depths of such lasers are very low and...
Article
Full-text available
Carbon fibre-reinforced polymer (CFRP) composites have found wide applications in the aerospace, marine, sports and automotive industries owing to their lightweight and acceptable mechanical properties compared to the commonly used metallic materials. Machining of CFRP composites using lasers can be challenging due to inhomogeneity in the material...
Article
A technique for electrode production within diamond using a femtosecond laser system is described. Diagnosis tests to quantify the stress, the diamond to graphite ratio, and the resistivity of these electrodes are discussed. A 3D electronic grade single crystal diamond detector produced using this technique is shown, and the electrodes have a resis...
Article
To form a 3D diamond detector electrodes were produced in diamond by a femtosecond laser-induced phase transition of diamond to graphite. The process parameters were varied to study the influence on electrode resistivity and induced stress. A technique for a relative measurement of stress induced in 3D diamond detectors is described. The detector w...
Article
Full-text available
A novel device using single-crystal chemical vapour deposited diamond and resistive electrodes in the bulk forming a 3D diamond detector is presented. The electrodes of the device were fabricated with laser assisted phase change of diamond into a combination of diamond-like carbon, amorphous carbon and graphite. The connections to the electrodes of...
Article
Full-text available
A novel device using single-crystal chemical vapour deposited diamond and re-sistive electrodes in the bulk forming a 3D diamond detector is presented. The electrodes of the device were fabricated with laser assisted phase change of diamond into a combination of diamond-like carbon, amorphous carbon and graphite. The connections to the electrodes o...
Article
Laser cleaning is a promising surface preparation technique for applications in high value manufacturing industries. However, understanding the effects of laser processing parameters on various types of contaminants and substrates, is vital to achieve the required cleaning efficacy and quality. In this paper, a two-dimensional transient numerical s...
Article
Full-text available
An aerospace grade Ti-6Al-4V alloy, treated by an excimer laser, has been analysed by elemental depth profiling using glow discharge optical emission spectrometry (GDOES). Laser exposure may modify the surface morphology of the alloy due to melting and generation of microcracks. Melting reduces the roughness over an area of 1 × 1 μm, whereas the ro...
Article
This paper reports the formation of uniform single layer micro-patterns of graphene on a glass substrate using direct femtosecond laser cutting. The cutting of graphene was achieved in air and argon. By translating the graphene sample with respect to the laser beam, continuous micro-channels were carved. The cutting geometry can be controlled by va...
Article
Lasers are extensively employed in cutting alumina sheets in the electronic industries. An important quality factor of laser cutting is striation (periodical lines) formation on the cut surfaces, which affects the surface roughness and geometry precision of laser cut products. The elimination of striation is important for laser cutting of alumina s...
Article
A major challenge in laser fusion cutting of thick-section ceramics is to overcome the thermal-stress induced cracking, which leads to catastrophic breakdown of the material integrity. In order to achieve crack-free cutting of ceramics, it is important to understand the mechanism of the transient temperature field and resulting stress distribution...
Article
A method for crack-free machining of deep cavity in alumina is demonstrated using a low-cost CO2 continuous wave (CW) laser. CO2 laser underwater machining has been found to result in reducing substrate defects such as recast layer, dross, cracking and heat damages that are typically found in machining in air. Finite Element (FE) modelling techniqu...
Article
The potential of using the laser ablation process to perform controlled stripping of titanium aluminium nitrite (TiAlN) coating from tungsten carbide (WC) substrate is explored in this paper. TiAlN coatings are extensively used in cutting tools to improve machining capability, and to extend the life of the tools. However, if any error is detected o...
Article
Direct laser surface micro/nanopatterning by using Contact Particle Lens Array (CPLA) has been widely utilized. The method involves laser scanning of a monolayer of transparent particles arranged on the substrate to be patterned. Despite the different techniques available for CPLA deposition; the particles monolayer can only be formed on hydrophili...
Article
This paper reports an investigation of the characteristics of human dentine ablated by a femtosecond laser of 800 nm wavelength for potential pain free dental restoration applications. The work has shown that precise femtosecond laser ablation with clear boundaries and without cracks and debris can be obtained. The transmittance of the dentine tiss...
Article
Full-text available
This paper reports an investigation into the characteristics of femtosecond laser (800-nm central wavelength) in the ablation of human dental enamel, dentine, and cementum at various laser fluences from 0.2 to 3.68 J/cm(2) with single and multiple pulses. The femtosecond laser interaction with cementum is reported for the first time. Ablation thres...
Article
The demand for micromachining of coronary stents by means of industrial lasers rises quickly for treating coronary artery diseases, which cause more than one million deaths each year. The most widely used types of laser for stent manufacturing are Nd:YAG laser systems with a wavelength of 1064 nm with pulse lengths of 10−3–10−2seconds. Considerable...
Article
In medical coronary stent fabrication, high precision profile cutting with minimum post-processing is desirable. Existing methods of profiling thin tubular metallic materials are based mainly on the use of Nd:YAG lasers. In recent studies fibre lasers have been used for stent cutting. However, for profiling thin (<4 mm diameter, < 200 μm wall thick...
Article
Current environmental challenges require sustainable and extended use and re-use of materials. For example, the service life of engineering tooling can be extended by using thin film coatings such as titanium nitride (TiN). However, when errors arise in the coating process or when the tooling needs to be re-used it is necessary to remove the coatin...
Article
Full-text available
A practical approach to a well-known technique of laser micro/nano-patterning by optical near fields is presented. It is based on surface patterning by scanning a Gaussian laser beam through a self-assembled monolayer of silica micro-spheres on a single-crystalline silicon (Si) substrate. So far, the outcome of this kind of near-field patterning ha...
Article
Full-text available
Although laser surface nanopatterning by particle lens arrays (PLA), utilizing near-field enhancement, has been extensively utilized previously, a suitable technique for the deposition of PLA on the curved surface of a cylinder was not available. In this paper, a novel technique for nanopatterning on curved surfaces using PLA is demonstrated. In th...
Article
Superior structural capabilities and lightweight of carbon-fibre-reinforced polymer composites have made their applications increasingly noticeable particularly in the aerospace and automotive industries for reduced fuel consumption. Anisotropic and heterogeneous features of these materials, however, have been prohibiting the application of laser c...
Article
Full-text available
By rapidly scanning a 532 nm diode pumped Nd:YVO 4 laser beam at nano-second pulses and below the ablation threshold, a uniform array of nano-bumps of less than 2 nm in height (diameter of around 20 µm) has been generated on a p-type <100> Si wafer. This height is two orders of magnitude lower than previously reported values. They were generated at...
Chapter
The process of dentine removal by ultra-short pulse laser is a promising technique for pain-free dental restoration. The aim of this work was to analyze the characteristics of human dentine ablated by a fs-laser of 800 nm wavelength and 1 kHz repetition rate. Precise ablation with clear boundary whereas without cracks and debris can be obtained. Th...
Article
Nitinol (a shape memory nickel-titanium alloy) is one of the desirable materials for medical stents applications, due to its high corrosion resistance, self-expansion and biocompatibility. The stents are commonly fabricated by using Nd:YAG laser cutting. As a result of long pulses (10-3-10 -2 seconds) of these lasers, considerable post processing i...
Article
High precision laser micromachining is extensively used in medical device industry. In medical stent fabrication, the processed stents must exhibit mechanically robust structures and high surface quality. High cost of post processing requires high accuracy in machining. Small and thin tubes heat up quickly and it is crucial to manage heat distribut...
Article
Laser surface micro/nanopatterning by using Contact Particles Lens Array (CPLA) has been extensively utilized but there is no suitable technique for deposition of CPLA on Hydrophobic surfaces. In this research a novel technique for patterning of hydrophobic surfaces has been proposed and demonstrated. For the deposition of CPLA, conventional techni...
Article
Laser surface patterning by Contact Particle Lens Arrays (CPLA), utilizing near field enhancement, has been extensively utilized previously. In the process a solution of Contact Particles is spread on the substrate surface which dries to form a monolayer of CPLA on the substrate. The monolayer of the particles is then scanned by a laser to form pat...
Conference Paper
Laser surface micro/nanopatterning by using Contact Particles Lens Array (CPLA) has been extensively utilized but there is no suitable technique for deposition of CPLA on Hydrophobic surfaces. In this research a novel technique for patterning of hydrophobic surfaces has been proposed and demonstrated. For the deposition of CPLA, conventional techni...
Conference Paper
High precision laser micromachining is extensively used in medical device industry. In medical stent fabrication, the processed stents must exhibit mechanically robust structures and high surface quality. High cost of post processing requires high accuracy in machining. Small and thin tubes heat up quickly and it is crucial to manage heat distribut...
Conference Paper
Laser surface patterning by Contact Particle Lens Arrays (CPLA), utilizing near field enhancement, has been extensively utilized previously. In the process a solution of Contact Particles is spread on the substrate surface which dries to form a monolayer of CPLA on the substrate. The monolayer of the particles is then scanned by a laser to form pat...
Conference Paper
Nitinol (a shape memory nickel-titanium alloy) is one of the desirable materials for medical stents applications, due to its high corrosion resistance, self-expansion and biocompatibility. The stents are commonly fabricated by using Nd:YAG laser cutting. As a result of long pulses (10⁻³-10⁻² seconds) of these lasers, considerable post processing is...
Article
This work reports on the technical feasibility and establishment of a process window for removing chromium titanium aluminium nitride (CrTiAlN) coating from steel substrates by laser irradiation. CrTiAlN coating has high hardness and oxidation resistance, with applications for use with cutting tools. The motivation for removing such coatings is to...
Article
Full-text available
We present results on the growth of highly organised, reproducible, periodic microstructure arrays on a stainless steel substrate using multi-pulsed Nd:YAG (wavelength of 1064 nm, pulse duration of 7 ns, repetition rate of 25 kHz, beam quality factor of M 2∼1.5) laser irradiation in standard atmospheric environment (room temperature and normal pres...
Article
Full-text available
Writing nano-sized features less than the diffraction limit of the lasers efficiently over a large area requires special technology development. This paper reports the use of a self-assembled particle lens array with near-field enhancement effect to write millions of nano-sized user-defined features, e.g. English letters, lines, curves, simultaneou...
Article
Full-text available
In recent years, laser ablation in liquid has become an increasingly important technique for the fabrication of nanoparticles (NPs). To date, only pulsed lasers have been used. This paper reports our recent studies on the generation of Ti-oxide and Ni-oxide NPs by the ablation of metal targets in aqueous environments using a high-power, high-bright...
Conference Paper
The demand for efficient, alternative sources of energy is a growing and crucial issue in today’s world. Solar energy offers a vast, inexhaustible, free and clean option for future power needs. Although new technologies emerge every day, silicon-based solar panels represent the most feasible and commercial solution. The reason for this is its well...
Article
Full-text available
Based on medium-tuned optical field enhancement effect around a self-assembled particle-lens array (PLA) irradiated with a femtosecond (fs) laser source, we demonstrated that high-precision periodical array of micro/nano-structures can be readily fabricated on glass surface or inside glass in large areas in parallel without any cracks or debris. Th...
Article
The authors present a simple and efficient technique for producing hexagonal arrays of nanostructures on silicon surfaces in chemical solutions. It utilizes the effect of optical near-field enhancement by self-assembled particle-lens arrays and a thermally induced chemical reaction with an alkaline solution. About 108 features can be produced simu...
Article
Full-text available
Studies have shown excimer laser cleaning to be an effective non-chemical alternative method for removing contaminants from surfaces of titanium alloys in preparation for electron beam welding and diffusion bonding, with reference to aerospace applications. Among several important criteria for process acceptability, is the absence of oxide formatio...
Article
Full-text available
Utilising a Nd:YVO4 laser (wavelength of 532nm, pulse duration of 8ns, repetition rate of 30kHz) and a Nd:YAG laser (wavelength of 1064nm, pulse duration of 7ns, repetition rate of 25kHz), it was found that during the pulsed laser ablation of metal targets, such as stainless steel, periodic nodular microstructures (microcones) with average periods...
Article
Full-text available
In understanding of the hot spot phenomenon in single-molecule surface enhanced Raman scattering (SM-SERS), the electromagnetic field within the gaps of dimers (i.e., two particle systems) has attracted much interest as it provides significant field amplification over single isolated nanoparticles. In addition to the existing understanding of the d...
Article
Parallel surface nanopatterning by the enhanced optical near-field under small transparent parti-cles has attracted great attention in recent years. The technique offers great versatility for producing nano-features on the sample surface based on the near-field ablation, etching, deposition and surface modification. Theoretical investigation of the...
Article
Nanopattering of silicon substrates using near-field enhancement by particle-lens arrays in a chemical solution is presented for the first time. Both experimental and theoretical investigations have been carried out to understand the properties of the nanopatterns produced. The obtained results proved that the developed nanofabrication technique is...
Article
Parallel surface patterning using micro particles is an attractive technique developed in recent years for large-area surface nanofabrication. It utilizes self-assembled particles lens-arrays, which convert the laser beam into a multiplicity of enhanced optical spots in parallel at focus. The focus of the particle is generally confined to a small r...
Conference Paper
Nanopattering of silicon substrates using near-field enhancement by particle-lens arrays in a chemical solution is presented for the first time. Both experimental and theoretical investigations have been carried out to understand the properties of the nanopatterns produced. The obtained results proved that the developed nanofabrication technique is...
Conference Paper
Nanopattering of silicon substrates using near-field enhancement by particle-lens arrays in a chemical solution is presented for the first time. Both experimental and theoretical investigations have been carried out to understand the properties of the nanopatterns produced. The obtained results proved that the developed nanofabrication technique is...
Conference Paper
This work reports on a technical feasibility and establishment of a process window for decoating of Chromium Titanium Aluminium Nitride (CrTiAlN) coating from steel substrates by laser stripping. CrTiAlN coating has a high hardness and oxidation resistance and finds application in cases such as cutting tools. The motivation for removing such coatin...
Conference Paper
Parallel surface patterning using micro particles is an attractive technique developed in recent years for large-area surface nanofabrication. It utilizes self-assembled particles lens-arrays, which convert the laser beam into a multiplicity of enhanced optical spots in parallel at focus. The focus of the particle is generally confined to a small r...
Article
Full-text available
Laser surface nanopattering using near-field enhancement by particle-lens arrays is studied. Ex-perimental and theoretical investigations are made in order to clarify the properties of the nano-patterns produced. The obtained results show that this nanofabrication technique is a flexible method for precise surface nanopatterning. A close-packed mon...
Article
Full-text available
The authors present a simple and efficient technique for laser writing of arbitrary nanopatterns across a large surface area without using projection masks. It is based on the unique near-field focusing effect of a self-assembled particle array on the surface interacting with an angular incident laser beam. The spot resolution can be down to 80 nm...
Article
Direct parallel writing nano-patterns over a large surface area is a challenging task. Techniques like electron beam and focused ion beam lithography are limited to particular applications because of low throughput and expensive setup. In this paper, an efficient and low-cost technique is reported on direct laser surface nanopatterning in the near-...
Conference Paper
Since their invention just over 20 years ago, optical traps have emerged as a powerful tool with broad-reaching applications in biology, physics and now potentially engineering. Capabilities have evolved from simple manipulation to the application of calibrated forces on—and the measurement of nanometer-level displacements of optically trapped obje...
Conference Paper
Direct parallel writing nano-patterns over a large surface area is a challenging task. Techniques like electron beam and focused ion beam lithography are limited to particular applications because of low throughput and expensive setup. In this paper, an efficient and low-cost technique is reported on direct laser surface nanopatterning in the near-...
Article
Laser jacket stripping of the two-layer polymer jacket coating of Corning SMF-28 silica fibres has been studied as an alternative approach to chemical and mechanical techniques. These polymer outer layers, although chemically similar, become discernable through laser ablation and depth per pulse experiments. Etch rate measurements using nanosecond...
Article
Full-text available
Since their invention just over 20 years ago, optical traps have emerged as a powerful tool with broad- reaching applications in biology, physics and now potentially engineering. Capabilities have evolved from simple manipulation to the application of calibrated forces on—and the measurement of nanometer-level displacements of optically trapped obj...

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