Diffraction Model of Thermoreflectance Data

Diffraction based mathematical model is developed to address the issue of spatial resolution in thermoreflectance imaging at the scale of 1 and 10 μm. Thermoreflectance imaging provided non-contact temperature measurement at micro and nano scale but the spatial resolution is limited by diffraction. By virtue of this work mathematical model is developed for the analysis of thermoreflectance data. In the development of model both the diffraction occurring at sample and substrate is combined to calculate intensity of thermoreflectance signal. This model takes into account the effective optical distance, sample width, wavelength, signal phase shift and reflectance intensity. Model shows qualitative and quantitative agreement with experimental data for the two wavelengths under investigation, 470 nm and 535 nm

INTRACELLULAR SUBSURFACE IMAGING USING A HYBRID SHEAR-FORCE FEEDBACK/ SCANNING QUANTITATIVE PHASE MICROSCOPY TECHNIQUE.

Quantitative phase microscopy (QPM) allows for the imaging of translucent or transparent biological specimens without the need for exogenous contrast agents. This technique is usually applied towards the investigation of simple cells such as red blood cells which are typically enucleated and can be considered to be homogenous. However, most biological cells are nucleated and contain other interesting intracellular organelles. It has been established that the physical characteristics of certain subsurface structures such as the shape and roughness of the nucleus is well correlated with onset and progress of pathological conditions such as cancer. Although the acquired quantitative phase information of biological cells contains surface information as well as coupled subsurface information, the latter has been ignored up until now. A novel scanning quantitative phase imaging system unencumbered by 2p ambiguities is hereby presented. This system is incorporated into a shear-force feedback scheme which allows for simultaneous phase and topography determination. It will be shown how subsequent image processing of these two data sets allows for the extraction of the subsurface component in the phase data and in vivo cell refractometry studies. Both fabricated samples and biological cells ranging from rat fibroblast cells to malaria infected human erythrocytes were investigated as part of this research. The results correlate quite well with that obtained via other microscopy techniques

Novel developments of Moiré techniques for industrial applications.

The family of moire and fringe projection techniques can be used to measure the shape, orientation and deformation of arbitrary objects. These experimental techniques are easy to automate, allow remote operation, provide full-field information and are versatile, inexpensive and relatively simple. They have been applied extensively in the past, but mostly in the controlled environment of a laboratory. There is great potential in the use of these techniques for a variety of industrial applications including quality control and process monitoring. However, this implies dealing with the adverse conditions of the factory, hangar or similar environment. In addition, these techniques will only appeal to industry if they are fast, simple, and foolproof. The main goal of this research was to exploit recent technological advances to fulfil the requirements of industry, making these techniques easier to use and more robust, and explore the potential offered by the combination and cross-fertilization of moire methods with techniques from different fields such as experimental stress analysis, non-destructive evaluation, and machine vision. This research resulted in the development of a number of instruments and procedures for industrial applications based in moire and fringe projection techniques, including: • A handheld instrument based in the shadow moire technique designed to assist in the detection of very small surface defects in aircraft parts, during in-service maintenance inspections; • A multi-purpose system to measure remotely (i) the shape and deformation of three dimensional objects by means of the fringe projection technique, and (ii) the location of the object by means of triangulation. The elements were integrated in a portable instrument, and fully automated novel algorithms were implemented to process the data; • Finally, a novel experimental technique is proposed that uses thermal marking to measure deformation in a component, in a combination of concepts from moire and thermography. Experimental results obtained in a range of situations are presented in several industrial applications in the context of the aerospace industry and in bioengineering

Development of a reinforcing fibre light-guide for use as a damage sensor within composite structures

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This study presents the results of an investigation to develop a novel sensor which would give a direct indication of the extent of impact damage in a composite. This was achieved by using glass reinforcing fibres to produce a light-guide, which was embedded within a composite laminate. The laminate was then subjected to impact events or bending stresses of sufficient magnitude to cause damage. The impact energies used in this study varied between 2 and 10 Joules, and the indentation depths varied between 0.125 and 1 mm, allowing damage propagation to be monitored. The fall-off in the transmitted light was used to monitor the level of damage, along with C-scanning and sectioning to provide reference data. The use of reinforcing fibres to produce the sensor meant that the strains required to cause failure in the fibres was realistically close to those of the composite constituents. Changes in the transmission characteristics of the sensor were found to correspond to real failure events occurring during impact.This study is funded by Mr D. Coward at Royal Mail Securities and the EPSRC

Quantitative phase imaging: advances to 3D imaging and applications to neuroscience

This thesis provides a brief overview of quantitative phase imaging (QPI) methods along with applications and advances made on them. First, spatial light interference microscopy (SLIM) is introduced as a QPI method extensively used in this thesis. Using this setup, an application of QPI in neuroscience is demonstrated by studying the emergent formation of a neuronal network. Second, an expansion of this QPI method into a 3D quantitative imaging method, called white-light diffraction tomography (WDT), has been shown. Lastly, an initial result for another advance in SLIM is introduced by combining SLIM with a programmable illumination. In the first part of this work, the emergent self-organization of a neuronal network has been demonstrated using the SLIM system. The emergent self-organization of a neuronal network in a developing nervous system is the result of a remarkably orchestrated process involving a multitude of chemical, mechanical and electrical signals. Little is known about the dynamic behavior of a developing network (especially in a human model) primarily due to a lack of practical and non-invasive methods to measure and quantify the process. Using the SLIM system, several fundamental properties of neuronal networks have been measured non-invasively from the sub-cellular to the cell population level. This method quantifies network formation in human stem cell derived neurons and shows correlations between trends in the growth, transport, and spatial organization of such a system, by utilizing the quantitative phase data with novel analysis tools, including dispersion-relation phase spectroscopy (DPS). A deeper understanding of neuronal network formation has been provided by studying filopodia dynamics in neurons. By measuring the dry mass change over time and several other new metrics, it is shown that the filopodia dynamics successfully reflect the expected neurite outgrowth. In the second part, white-light diffraction tomography (WDT) is introduced as a new approach for imaging microscopic transparent objects such as live unlabeled cells in 3D. The approach extends diffraction tomography to white light illumination and imaging rather than scattering plane measurements. The experiments were performed using the SLIM system. The axial dimension of the object was reconstructed by scanning the focus through the object and acquiring a stack of phase-resolved images. The 3D structures of live, unlabeled red blood cells are imaged and compared with confocal and scanning electron microscopy images. The 350 nm transverse and 900 nm axial resolution achieved allows us to reveal sub-cellular structures at high resolution in E. coli cells and HT29 cells. Furthermore, a 4D imaging capability, with the fourth dimension being time, has also been demonstrated. The WDT theory is further extended to explain light scattering through thick tissue, which is not in the single scattering regime. The obtained inverse scattering solution for thick samples is then related to the time-reversal theory, and it is proven that there are strong constraints for time-reversal to work. By introducing a few specific examples, including scattering through a particle and scattering through a grating, the physics of light scattering and time-reversal theory is deeply understood. Lastly, an upgrade to the SLIM system with a programmable illumination source, a projector, has been demonstrated. By replacing the ring illumination of PC with a ring-shaped pattern projected onto the condenser plane, results comparable to those of the original SLIM were recovered. This new method minimized the halo artifact of the imaging system by minimizing the effect of spatial coherence caused by the thickness of the illumination. Further application of this technique into optogenetics is introduced and the initial results are presented

Development of a traceability route for areal surface texture measurements

Modern manufacturing industry is beginning to benefit from the ability to control the three dimensional, or areal, structure of a surface. To underpin areal surface manufacturing, a traceable measurement infrastructure is necessary. In this thesis a practical realisation of areal surface traceability is presented, which includes the development of: a primary in-strument, methodologies for using the primary instrument to calibrate material measure-ment standards used as standard transfer artefacts, and the process of transferring this traceability to industrial users of stylus and optical instruments. The design of the primary instrument and its complex measurement uncertainty model are described, including detailed analysis of the input parameters of the uncertainty model and their effect on the co-ordinate measurements of the instrument. The development of the process of transferring the areal traceability to industrial users lead to a set of metrological characteristics applicable to all areal surface topography measuring instruments. The set of metrological characteristics, now included into international stand-ards, comprise of: measurement noise, flatness deviation, amplification, linearity and squareness, and resolution. Despite the differences in operation of the various types of in-strument, the idea behind this set of metrological characteristics is based on the fact that these instruments produce three dimensional data sets of points, which is a new approach in the field. Metrological characteristics are quantities that can be measured directly, gener-ally using calibrated material measures. The development of standard methodologies for calibrating the metrological characteristics, and the explicit relationship between the metro-logical characteristics and the measurement uncertainty associated with the co-ordinate measurements provided by the instrument is presented. Many of the techniques described in this thesis are now being discussed for inclusion into international standards