Over the last decade, high power fibre amplifiers and lasers have been rapidly developed and successfully commercialized for a number of industrial applications such as cutting, welding, and marking. The industrial fibre laser business is currently worth over $800M/year, with compound annual growth rate of about 13% - the highest among the different laser technologies. One of the main contributors to this success has been the significantly improved rare-earth doped fibre fabrication technologies. High performance fibres rely on controlled incorporation of refractive index modifying dopants, as well as, gain providing rare-earth ions. High efficiency, high average and/or peak power industrial fibre lasers and amplifiers invariably use large-mode area fibres with complex refractive indices and rare-earth distributions. In most cases, a number of different dopants are used simultaneously in order to control the refractive index and gain distribution, and through it the fibre modality and modal differential gain. Additional dopants are also used to reduce nonlinear effects, such as Stimulated Brillouin and Raman Scattering, and other parasitic effects, such as photodarkening. The various dopants have different sizes, mobility, and diffusion rates and, as a consequence, the resulting refractive index profiles can in general be much different to rare earth distributions within the core, and one cannot be inferred from the other. In addition, depending on the fabrication technique, the distribution of dopants is not uniform along the fibre preform, rendering the drawn fibre performance variable and "patchy". In particular, Modified Chemical Vapour Deposition (MCVD) fabrication technique, among the most versatile and widely used fabrication techniques, is known to suffer from poor repeatability and large variability along the preform length. This compromises significantly the fibre yield and increases the fibre cost. In addition, and even more importantly, currently there is no reliable information regarding the "fitness-for-purpose" of fibre in advance. Its suitability can only be tested and quantified after a full fibre laser has been built and thoroughly tested, adding considerably to the fibre laser module turn-around time, yield and cost. So there is a need for unsuitable preforms or parts of preform to be identified early in the fibre drawing process and be discarded. Another requirement has lately appeared in the fibre telecom area. Over the last few years there has been a strong resurgence in multimode telecom systems research, with spatial-division multiplexing (SDM) promising to solve the predicted forthcoming telecom capacity crunch. Successful development of SDM systems relies exclusively on the development of high performance multimode fibre amplifiers with carefully optimized rare-earth (Erbium or Thulium) profiles for modal gain equalization. Again, detailed and accurate knowledge of the active dopant distribution over the fibre cross-section along the entire preform length is critical for successful demonstrations of this game-changing approach to single-fibre transmission capacity increase. The main aim of this proposal is to develop widely applicable, non-destructive characterization techniques for the accurate and detailed determination of active-dopant distribution in fibre preforms and provide the required reliable information well before the preforms are drawn into fibres. Such preform characterization techniques are expected to have a big impact on the performance and cost of advanced high-power fibre laser systems, as well as, currently researched SDM telecom systems, and increase the competiveness of the UK manufacturing basis as well as enhance the UK cutting-edge research activities in these areas.

The aim of this project is to explore the use of laser-generated ultrasound in thermosonic (TS) bonding. TS bonding is a joining technique which uses a combination of heat, pressure and ultrasonic energy to facilitate the formation of strong metal-metal bonds. It is used mainly for attaching bond wires to silicon chips inside their packages, where it offers a number of advantages over other joining methods. For example, it involves no additional materials (e.g. solders or adhesives), and it can be carried out at lower temperature and pressure than thermo-compression bonding and lower ultrasonic power than pure ultrasonic welding. An important potential application for TS bonding is flip chip assembly, a technique used in advanced electronics manufacturing. Flip chip allows unpackaged integrated circuits to be attached to a circuit board or other substrate in a face-down configuration, with electrical connections between the contact pads on the chip and the substrate being provided by conducting "bumps". Flip chip assembly offers several advantages over other chip attachment methods, such as higher electrical performance, higher interconnect density (more electrical connections per unit area), smaller footprint and lower height. Flip chip processes based on solder attachment have been established for many years. However, with the continual drive for miniaturization they are approaching their limits in terms of interconnect density. Alternative approaches based on adhesive bonding are scalable to finer interconnect pitches, but do not achieve the performance or reliability required for many applications. TS bonding could form the basis of a highly reliable, ultra-fine-pitch flip chip technology. However, up to now it has proved challenging to develop robust processes, mainly because it is highly sensitive to co-planarity errors and bump height variations which can lead to bond strength non-uniformity and even damage to the chip. These issues become more severe as the chip size increases, and consequently TS flip chip has been limited to a narrow range of applications involving small devices with low interconnect count. We propose to develop a TS bonding process in which pulsed laser light is used to generate ultrasound locally at specific bonding sites, using confined ablation of a sacrificial carrier tape sandwiched between the workpiece and a transparent bond head. This approach will enable us to deliver the ultrasonic energy in a flexible manner, allowing for the possibility of compensating for co-planarity and bump height errors. With the proposed system it will also be possible to pre-heat the interface locally by laser, yielding a process with very low overall thermal loading. If successful, the proposed research will ultimately lead to a next generation flip chip technology with wide ranging applications in electronics manufacturing. The new process should also find applications in other fields such as MEMS (microelectromechanical systems) and optoelectronics where joining of delicate components is required.

Imagine a world where walking through a revolving door or archway allows "invisible light" (light outside our normal visual range) to generate detailed 3D images of any patient with high resolution! This is the global vision and targeted ambition of this 2050 proposal. This will allow us to target very early detection of disease using light (referred to as a non-ionising radiation technology) in association with fast computational methods and artificial intelligence (AI) to reconstruct images. This will be transformative, is a practical reality, and in addition potentially offers unique treatment options for the healthcare needs of 2050. These goals will be achieved by simultaneous interdisciplinary advances: - Harnessing of world-leading optical physics - with lasers that work at wavelengths of light that are invisible to the naked eye - akin to radio waves but with very different frequencies. - Rethinking of existing detector technology and development of layers of new chemistries and sensor materials to allow them to function at these "invisible colours" - Development of novel image restoration tools and new computational optics and imaging that will allow us to access information at depth that was previously hidden without any injection of dyes or causing inconvenience. - Validation of the technology on diseases that have huge impacts on quality of life and huge NHS costs, for example osteoarthritis and cancer. Why is this needed? (i). Bone disease: By 2050 there will be over 2 billion people aged over 60. This is wonderful news for us all, but will present a variety of healthcare challenges. For example it is predicted that the numbers of hip fractures worldwide will increase from 1.7 million in 1990 to 6.3 million in 2050. In addition, musculoskeletal conditions are worsened by the rising problem of obesity - that affects old and young alike with half the UK population predicted to be obese by 2050. Our technology will impact on these statistics. Detecting disease early and affordably and non-invasively will allow life-style changes to be made by patients (before it is too late) - leading to positive effects on quality of life and broad impact in relation to the NHS. (ii). Cancer: In the UK 1 in 2 of those born after 1960 will develop cancer with a 20% chance of dying from that cancer within 5 years. In 2050, as longevity has increased, the chances of someone getting cancer in their lifetime will be 8 in 10. Being able to influence these statistics will have dramatic impacts. Our vision is that non-invasive externally applied illumination sources - with micron precision - will be able to illuminate a tumour in a three-dimensional sense and destroy it. Driving patient health: Now think of the impact of what else the deeply penetrating and focused light might be able to do? Interacting with tissues selectively in a three-dimensional manner - could we hit activate drugs in a localised 3D pattern? Will we be able to drive fat cell metabolism? The possibilities are tremendous and we seek to address these in our research.

Lasers are used for an extremely wide range of manufacturing processes. This is due, in part, to their significant flexibility with respect to parameters such as pulse length, pulse energy, wavelength, and beam size. However, this flexibility comes at a price, namely the significant amount of time that must be dedicated to finding the optimal set of parameters, for each and every manufacturing process or customer specification. The standard practice in industry is the mechanical collection of laser machining data for all parameter combinations, in order to find the optimal combination of parameters. However, this process is both time-consuming and unfocussed, and it can take days or weeks, hence costing unnecessary time and money. Even when the optimal parameters have been determined, small changes, for example in laser power or beam shape, during manufacturing, can result in a final product quality that is below the required standard, once again costing time and money. There will also be instances where the specification is not known in advance due to variability in the manufacturing process. What is needed, therefore, are a series of methodologies for identifying optimal parameters before manufacturing, for providing real-time monitoring and error correction during manufacturing, and for enabling process-control (for example stopping the laser exactly at task completion, or varying the laser power for the final finishing steps). The research field of machine learning has seen some extremely significant developments in recent years, and it is now widely understood to be a catalyst for a fundamental change across almost all manufacturing industries. The objective of this proposal is to develop the technological and human expertise required for the integration of machine learning approaches into the UK laser-based manufacturing industry and the NHS. This proposal therefore seeks to leverage state-of-the-art machine learning techniques for solving well-known problems in laser-based manufacturing and materials processing, resulting in improvements in efficiency, reliability, and precision. The results of this proposal will lead to time and money savings for both the UK laser-based manufacturing industry and the NHS. This proposal will cover the application of neural networks for modelling and optimising of femtosecond laser machining, instantly identifying laser-based manufacturing parameters for any customer specification, automatically compensating for residual cavity effects in fibre lasers, enabling targeted delivery of laser light for psoriasis treatment, and laser welding process enhancement in real-time via multi-sensor data.

This innovative proposal seeks a ten-fold improvement in the energy efficiency and speed of laser based manufacturing. Exploiting the most recent advances in optical fibre communication technology we will develop a new generation of fibre lasers offering unprecedented levels of simultaneous control of the spatial, temporal and polarisation properties of the output beam. This will allow machinists to optimise the laser for particular light:matter interactions and to maximise the efficiency of each pulse in laser-based materials processing for the first time, enabling a step-change in manufacturing control and novel low-energy manufacturing processes. We believe that order of magnitide reductions in energy usage should be possible for many laser processes relative to the current generation of fibre lasers used in manufacturing today, (which themselves are already at least x2 more efficient than other diode-pumped solid-state lasers, and more than x10 more efficient than other laser technologies still in use in laser machine shops (e.g. flash-lamp pumped YAGs)). Importantly, the new control functionalities enabled should also allow laser based techniques to replace highly energy-inefficient mechanical processes currently used for certain high value manufacturing tasks and in particular in ultrafine polishing which will represent an important focus of the application work to be performed at the IfM. Lasers offering such exquiste control of the beam parameters at high peak and average powers, have the potential to be disruptive in a number of application spaces beyond industrial laser processing - in particular in sensing, imaging, medicine, defence and high energy physics and we will look to investigate opportunities to exploit our technology in these areas as the project evolves.