Showing papers by "John R. Tyrer published in 2016"

Use of a diffractive optic for high power laser cutting

Abstract: There is a current interest in using laser cutting for nuclear decommissioning applications. The benefits of using lasers for this application include the high speeds available, the tolerance of the process, the lightness of the cutting head, the lack of a reaction force with the part being cut, and the ease of automation of the laser cutting process. Of course laser cutting is a thermal process and a potential detriment, is that the residual laser beam, passing through the kerf, might damage or indeed set fire to something positioned behind the part being cut. This paper describes the use of a diffractive optical element in the laser beam forming optics, designed to extend the depth of focus of the system, without increasing the focal length of the focusing optic. In this way, for cutting thick materials, the goal is to achieve the cutting performance of a long focal length lens, with the beam divergence of a short focal length lens. A design of diffractive optical element is presented, which when used w...

Eye hazards of laser ‘pointers’ in perspective

Abstract: Eight years ago media coverage of incidents involving laser pointers in which individuals claimed to have suffered eye damage resulted in a perspective being published in this journal.1 The final sentence concluded ‘laser pointers, pens or key rings if used appropriately are not an eye hazard, and even if used inappropriately will not cause permanent eye damage’. This statement has been supported by the finding that until recently no irreversible eye injuries had been reported for a period of almost 15 years other than those caused by deliberate and prolonged viewing of laser beams.2 During this time period pointers have been freely available with an estimated 500 000 to c1.2 million laser pointers in circulation. Unfortunately this is now not the case. While the biophysics relating to eye injuries remains constant the nature and supply of current handheld devices have changed dramatically in the past 8 years. In the past, pointers predominantly produced red laser beams and were restricted to have an upper output limit of 1 mW and as such were classified as class 2 laser products. Safety was afforded by insufficient energy being able to pass into the eye before the targeted individual blinked and turned their head. In reality, as a result of both increased efficiency of modern devices and poor manufacturing compliance many of these devices classified as class 2 have outputs of between 0.5 and 300 mW. Clearly, they are mislabelled and should have been identified as class 3B laser products, which are not appropriate for general sale to the public. Today, low-cost laser ‘pointers’ producing green or red laser beams with output powers of 1000 mW can be found and indeed devices on the internet of between 1500 and 6000 mW are commercially available. These …

The role of light in measuring ocular biomechanics.

Abstract: The cornea is a highly specialised tissue with a unique set of biomechanical properties determined by its complex structure. The maintenance of these mechanical properties is fundamental to maintain clear vision as the cornea provides the majority of the focussing power of the eye. Changes to the biomechanics of the cornea can occur during ageing, disease, and trauma, or as a result of surgery. Recently there has been increased interest in the mechanical properties of the cornea as knowledge of these properties has significant implications for the improvement of current ocular treatments including PRK and LASIK, and for the diagnosis and tracking of corneal diseases and therapy such as keratoconus and crosslinking. Biomechanics are also important for the development of artificial corneal replacements. This paper describes the use of a novel, non-destructive lateral electronic speckle pattern shearing interferometer (ESPSI). The data generated via this technique give a full-field view of the mechanical response of the cornea under simulated physiological loading conditions, and enables strain and displacement to be determined in three planes. The technique allows corneal stiffness to be quantified and enables changes and non-homogeneities that occur due to surgery or disease to be detected.

Laser annealing of thin film CdTe solar cells using a 808 nm diode laser

Abstract: We report on the effect of a new laser annealing treatment for thin film CdTe solar cells using a 808 nm diode laser. As-deposited, laser annealed and MgCl 2 treated/laser annealed CdTe thin films have been analysed. One part of the work has been focused on understanding the efficacy of the activation treatment by laser annealing. The results show partial chlorine diffusion and associated partial re-crystallisation of the absorber. The second part of this work has been focused on the effect of the treatment on the chemical composition of the CdTe surface. It has been found that the process also contributes to the formation of a Te-rich layer on the surface of the CdTe absorber, which may provide a useful process to produce a back contact. This paper reveals the effect of the laser treatment on the microstructural properties of the CdTe absorber material. The microstructure has been analysed using STEM/EDX, HRTEM and XRD. Further work is required to optimise the process but it has the potential to provide much greater control than current activation methods and also to provide a Te back contact suitable for CdTe solar cells.

Using wire shaping techniques and holographic optics to optimize deposition characteristics in wire-based laser cladding.

Abstract: In laser cladding, the potential benefits of wire feeding are considerable. Typical problems with the use of powder, such as gas entrapment, sub-100% material density and low deposition rate are all avoided with the use of wire. However, the use of a powder-based source material is the industry standard, with wire-based deposition generally regarded as an academic curiosity. This is because, although wire-based methods have been shown to be capable of superior quality results, the wire-based process is more difficult to control. In this work, the potential for wire shaping techniques, combined with existing holographic optical element knowledge, is investigated in order to further improve the processing characteristics. Experiments with pre-placed wire showed the ability of shaped wire to provide uniformity of wire melting compared with standard round wire, giving reduced power density requirements and superior control of clad track dilution. When feeding with flat wire, the resulting clad tracks showed a greater level of quality consistency and became less sensitive to alterations in processing conditions. In addition, a 22% increase in deposition rate was achieved. Stacking of multiple layers demonstrated the ability to create fully dense, three-dimensional structures, with directional metallurgical grain growth and uniform chemical structure.

Laser processing of printed copper interconnects on polymer substrates

Abstract: With the increasing demand for integration of electronics embedded within devices there has been a consequent increase in the requirement for the deposition of electrically conductive materials to form connecting tracks on or within non-traditional substrate materials, such as temperature sensitive polymers, that may also have non-planar surfaces. In this work, micron scale copper powder based materials were deposited onto acrylic and glass substrates and then selectively laser processed to form electrically conductive copper tracks. Before deposition, the copper powder was chemically treated to remove the surface oxide and subsequently protected with a self-assembled monolayer coating. The copper was then patterned onto the substrate either as a dry powder confined within pre-formed grooves, or was combined with a binder to be printed as a paste. A CO 2 laser was then used to heat the copper powder in air, leading to tracks that showed good electrical conductivity. At low laser power levels, the tracks appeared largely unchanged from the original material, but showed measureable conductivity. With higher laser power levels the tracks showed evidence of partial melting of the surface layers and further reductions in resistivity, to values approximately 30 times those of bulk copper, were obtained.