Laser-induced breakdown spectroscopy applied to pasture, titanium, and bioplastics

Precision agriculture is a farming practice that makes production more efficient. Farmers are able to treat infield variability optimising efficiency, growth, and yield by tailoring the time, rate, and type of fertilizer that is applied. This reduces costs, waste, and environmental side effects such as runoff and leaching caused by overfertilization. Precision agriculture technology measures the nutritional status of crops to inform what, and where, nutrients are needed. The sensors need to be precise, discriminative, and work in real time to ensure that optimal windows for nutrition are not missed. These sensor systems provide aerial imaging, and crop, or soil, colour index maps. A technology that has proven effective on some agricultural specimens is laserinduced breakdown spectroscopy (LIBS). LIBS is an optical emission technique that utilizes a high-powered pulsed laser to create a plasma on the sample surface. As the plasma cools, photons are emitted at distinct wavelengths corresponding to the elemental composition in the plasma, which should represent the sample. This thesis investigates using LIBS as a sensor for precision agriculture. Multiple chemometric methods have been used on the pasture spectra to build calibration models. There are large deviations between spectra belonging to a single sample. This is due to surface inhomogeneity, particle size, lens-to-sample distance, temperature fluctuations between plasmas, and other causes. Temperature corrections were investigated using Boltzmann plots, Saha-Boltzmann plots, and intensity ratios. With limited success in mitigating the variations in pasture spectra, LIBS was used to investigate non-aqueous systems. The ability to selectively sinter the surface of injection moulded titanium was examined. Titanium metal injection moulding allows the creation of complex metal parts that are lightweight, biocompatible, and costs less than machining. Multiple LIBS pulses produced sintering in the ablation crater of injection moulded titanium by sufficiently heating the titanium particles so that fusion occurred. The spectra from LIBS can be used to monitor the extent to which the surface is sintered by measuring the reduction in carbon emissions. An autofocus system, based on the triangulation method, was used to minimise variations caused by lens-to-sample distance (LTSD). With the success of sintering titanium, LIBS was used to investigate non-aqueous organic systems. Employing LIBS to discriminate bioplastics from regular plastics was explored in recycle waste streams. If bioplastics are present in the recovery process of regular plastics the resulting product contains impurities. This study was undertaken to determine the feasibility of incorporating bioplastics in the curbside pickup of recyclables in New Zealand. The common recyclables are plastics, glass, tin cans, and aluminium cans. The setup was designed to emulate a one-shot LIBS detection system in a recycling plant. Models were created using k nearest neighbours and soft independent modelling class analogy from the spectra. 100 % discrimination between bioplastics and regular plastics was achieved. An autofocus system, combining dual lasers, was used to overcome the occlusions produced by sample geometry

Laser-Induced Plasma and its Applications

The laser irradiation have shown a range of applications from fabricating, melting, and evaporating nanoparticles to changing their shape, structure, size, and size distribution. Laser induced plasma has used for different diagnostic and technological applications as detection, thin film deposition, and elemental identification. The possible interferences of atomic or molecular species are used to specify organic, inorganic or biological materials which allows critical applications in defense (landmines, explosive, forensic (trace of explosive or organic materials), public health (toxic substances pharmaceutical products), or environment (organic wastes). Laser induced plasma for organic material potentially provide fast sensor systems for explosive trace and pathogen biological agent detection and analysis. The laser ablation process starts with electronic energy absorption (~fs) and ends at particle recondensation (~ms). Then, the ablation process can be governed by thermal, non-thermal processes or a combination of both. There are several types of models, i.e., thermal, mechanical, photophysical, photochemical and defect models, which describe the ablation process by one dominant mechanism only. Plasma ignition process includes bond breaking and plasma shielding during the laser pulse. Bond breaking mechanisms influence the quantity and form of energy (kinetic, ionization and excitation) that atoms and ions can acquire. Plasma expansion depends on the initial mass and energy in the plume. The process is governed by initial plasma properties (electron density, temperature, velocity) after the laser pulse and the expansion medium. During first microsecond after the laser pulse, plume expansion is adiabatic afterwards line radiation becomes the dominant mechanism of energy loss

Laser-induced breakdown spectroscopy in Asia

Laser-induced breakdown spectroscopy (LIBS) is an analytical detection technique based on atomic emission spectroscopy to measure the elemental composition. LIBS has been extensively studied and developed due to the non-contact, fast response, high sensitivity, real-time and multi-elemental detection features. The development and applications of LIBS technique in Asia are summarized and discussed in this review paper. The researchers in Asia work on different aspects of the LIBS study in fundamentals, data processing and modeling, applications and instrumentations. According to the current research status, the challenges, opportunities and further development of LIBS technique in Asia are also evaluated to promote LIBS research and its applications

Plant Responses and Tolerance to Salt Stress: Physiological and Molecular Interventions

Overall, the 19 contributions in this Special Issue “Plant Responses and Tolerance to Salt Stress: Physiological and Molecular Interventions” discuss the various aspects of salt stress responses in plants. It also discusses various mechanisms and approaches to conferring salt tolerance on plants. These types of research studies provide further directions in the development of crop plants for the saline environment in the era of climate change